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Postgres Extensions to the JDBC API

Postgres is an extensible database system. You can add your own functions to the backend, which can then be called from queries, or even add your own data types.

Now, as these are facilities unique to us, we support them from Java, with a set of extension API's. Some features within the core of the standard driver actually use these extensions to implement Large Objects, etc.

Accessing the extensions

To access some of the extensions, you need to use some extra methods 
in the postgresql.Connection class. In this case, you would need to 
case the return value of Driver.getConnection().

For example:

    Connection db = Driver.getConnection(url,user,pass);

    // later on
    Fastpath fp = ((postgresql.Connection)db).getFastpathAPI();

Class postgresql.Connection
                                
java.lang.Object
   |
   +----postgresql.Connection

   public class Connection extends Object implements Connection

These are the extra methods used to gain access to our extensions. I 
have not listed the methods defined by java.sql.Connection.

 public Fastpath getFastpathAPI() throws SQLException

          This returns the Fastpath API for the current connection.

          NOTE: This is not part of JDBC, but allows access to 
functions on the postgresql backend itself.

          It is primarily used by the LargeObject API

          The best way to use this is as follows:

 import postgresql.fastpath.*;
 ...
 Fastpath fp = ((postgresql.Connection)myconn).getFastpathAPI();

          where myconn is an open Connection to postgresql.

        Returns:
                Fastpath object allowing access to functions on the 
postgresql backend.

        Throws: SQLException
                by Fastpath when initialising for first time
          
 public LargeObjectManager getLargeObjectAPI() throws SQLException

          This returns the LargeObject API for the current connection.

          NOTE: This is not part of JDBC, but allows access to 
functions on the postgresql backend itself.
   
          The best way to use this is as follows:

 import postgresql.largeobject.*;
 ...
 LargeObjectManager lo = 
((postgresql.Connection)myconn).getLargeObjectAPI();

          where myconn is an open Connection to postgresql.

        Returns:
                LargeObject object that implements the API

        Throws: SQLException
                by LargeObject when initialising for first time

 public void addDataType(String type,
                         String name)

          This allows client code to add a handler for one of 
postgresql's more unique data types. Normally, a data type not known 
by the driver is returned by ResultSet.getObject() as a PGobject 
instance.

This method allows you to write a class that extends PGobject, and 
tell the driver the type name, and class name to use.

The down side to this, is that you must call this method each time a 
connection is made.

          NOTE: This is not part of JDBC, but an extension.

          The best way to use this is as follows:

 ...
 ((postgresql.Connection)myconn).addDataType("mytype","my.class.name"-
);
 ...

          where myconn is an open Connection to postgresql.

          The handling class must extend postgresql.util.PGobject

        See Also:
                PGobject

Fastpath

Fastpath is an API that exists within the libpq C interface, and 
allows a client machine to execute a function on the database backend. 
Most client code will not need to use this method, but it's provided 
because the Large Object API uses it.

To use, you need to import the postgresql.fastpath package, using the 
line:
     import postgresql.fastpath.*;

Then, in your code, you need to get a FastPath object:
     Fastpath fp = ((postgresql.Connection)conn).getFastpathAPI();

This will return an instance associated with the database connection 
that you can use to issue commands. The casing of Connection to 
postgresql.Connection is required, as the getFastpathAPI() is one of 
our own methods, not JDBC's.

Once you have a Fastpath instance, you can use the fastpath() methods 
to execute a backend function.

Class postgresql.fastpath.Fastpath

java.lang.Object
   |
   +----postgresql.fastpath.Fastpath

   public class Fastpath

   extends Object

   This class implements the Fastpath api.

   This is a means of executing functions imbeded in the postgresql 
backend from within a java application.

   It is based around the file src/interfaces/libpq/fe-exec.c

   See Also:
          FastpathFastpathArg, LargeObject

Methods

 public Object fastpath(int fnid,
                        boolean resulttype,
                        FastpathArg args[]) throws SQLException

          Send a function call to the PostgreSQL backend
          
        Parameters:
                fnid - Function id
                resulttype - True if the result is an integer, false 
for
                other results
                args - FastpathArguments to pass to fastpath

        Returns:
                null if no data, Integer if an integer result, or 
byte[]
                otherwise
         
        Throws: SQLException
                if a database-access error occurs.

 public Object fastpath(String name,
                        boolean resulttype,
                        FastpathArg args[]) throws SQLException

          Send a function call to the PostgreSQL backend by name. 

Note:
          the mapping for the procedure name to function id needs to 
exist, usually to an earlier call to addfunction(). This is the 
prefered method to call, as function id's can/may change between 
versions of the backend. For an example of how this works, refer to 
postgresql.LargeObject

        Parameters:
                name - Function name
                resulttype - True if the result is an integer, false 
for
                other results
                args - FastpathArguments to pass to fastpath

        Returns:
                null if no data, Integer if an integer result, or 
byte[]
                otherwise

        Throws: SQLException
                if name is unknown or if a database-access error 
occurs.

        See Also:
                LargeObject
          
 public int getInteger(String name,
                       FastpathArg args[]) throws SQLException

          This convenience method assumes that the return value is an 
Integer

        Parameters:
                name - Function name
                args - Function arguments

        Returns:
                integer result

        Throws: SQLException
                if a database-access error occurs or no result

 public byte[] getData(String name,
                       FastpathArg args[]) throws SQLException

          This convenience method assumes that the return value is 
binary data

        Parameters:
                name - Function name
                args - Function arguments

        Returns:
                byte[] array containing result

        Throws: SQLException
                if a database-access error occurs or no result

 public void addFunction(String name,
                         int fnid)

          This adds a function to our lookup table.

          User code should use the addFunctions method, which is based 
upon a query, rather than hard coding the oid. The oid for a function 
is not guaranteed to remain static, even on different servers of the 
same version.

        Parameters:
                name - Function name
                fnid - Function id

 public void addFunctions(ResultSet rs) throws SQLException
                       
          This takes a ResultSet containing two columns. Column 1 
contains the function name, Column 2 the oid.

          It reads the entire ResultSet, loading the values into the 
function table.

          REMEMBER to close() the resultset after calling this!!

          Implementation note about function name lookups:
          
          PostgreSQL stores the function id's and their corresponding 
names in the pg_proc table. To speed things up locally, instead of 
querying each function from that table when required, a Hashtable is 
used. Also, only the function's required are entered into this table, 
keeping connection times as fast as possible.

          The postgresql.LargeObject class performs a query upon it's 
startup, and passes the returned ResultSet to the addFunctions() 
method here.
       
          Once this has been done, the LargeObject api refers to the 
functions by name.
          
          Dont think that manually converting them to the oid's will 
work. Ok, they will for now, but they can change during development 
(there was some discussion about this for V7.0), so this is 
implemented to prevent any unwarranted headaches in the future.

        Parameters:
                rs - ResultSet

        Throws: SQLException
                if a database-access error occurs.
          
        See Also:
                LargeObjectManager

 public int getID(String name) throws SQLException
          
          This returns the function id associated by its name
          
          If addFunction() or addFunctions() have not been called for 
this name, then an SQLException is thrown.

        Parameters:
                name - Function name to lookup

        Returns:
                Function ID for fastpath call

        Throws: SQLException
                is function is unknown.

Class postgresql.fastpath.FastpathArg

java.lang.Object
   |
   +----postgresql.fastpath.FastpathArg

   public class FastpathArg extends Object
        
   Each fastpath call requires an array of arguments, the number and 
type dependent on the function being called.

   This class implements methods needed to provide this capability.

   For an example on how to use this, refer to the 
postgresql.largeobject package

   See Also:
          Fastpath, LargeObjectManager, LargeObject

Constructors

 public FastpathArg(int value)
 
          Constructs an argument that consists of an integer value

        Parameters:
                value - int value to set

 public FastpathArg(byte bytes[])
          
          Constructs an argument that consists of an array of bytes

        Parameters:
                bytes - array to store

 public FastpathArg(byte buf[],
                    int off,
                    int len)

           Constructs an argument that consists of part of a byte 
array

        Parameters:
                buf - source array
                off - offset within array
                len - length of data to include

 public FastpathArg(String s)
          
          Constructs an argument that consists of a String.
      
        Parameters:
                s - String to store

Geometric Data Types

PostgreSQL has a set of datatypes that can store geometric features 
into a table. These range from single points, lines, and polygons.

We support these types in Java with the postgresql.geometric package.

It contains classes that extend the postgresql.util.PGobject class. 
Refer to that class for details on how to implement your own data type 
handlers.

Class postgresql.geometric.PGbox

java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.geometric.PGbox

   public class PGbox extends PGobject implements Serializable, 
Cloneable

   This represents the box datatype within postgresql.

Variables

 public PGpoint point[]

          These are the two corner points of the box.

Constructors

 public PGbox(double x1,
              double y1,
              double x2,
              double y2)

        Parameters:
                x1 - first x coordinate
                y1 - first y coordinate
                x2 - second x coordinate
                y2 - second y coordinate

 public PGbox(PGpoint p1,
              PGpoint p2)

        Parameters:
                p1 - first point
                p2 - second point

 public PGbox(String s) throws SQLException
                            
        Parameters:
                s - Box definition in PostgreSQL syntax

        Throws: SQLException
                if definition is invalid
                
 public PGbox()

          Required constructor
              
Methods

 public void setValue(String value) throws SQLException
                
          This method sets the value of this object. It should be 
overidden, but still called by subclasses.
                            
        Parameters:
                value - a string representation of the value of the 
object
        Throws: SQLException
                thrown if value is invalid for this type

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
                
        Returns:
                true if the two boxes are identical
          
        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class PGobject
   
 public String getValue()
        
        Returns:
                the PGbox in the syntax expected by postgresql

        Overrides:
                getValue in class PGobject

Class postgresql.geometric.PGcircle

java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.geometric.PGcircle
        
   public class PGcircle extends PGobject implements Serializable, 
Cloneable
               
   This represents postgresql's circle datatype, consisting of a point 
and a radius

Variables

 public PGpoint center
           
          This is the centre point
 
public double radius
           
          This is the radius
   
Constructors   

 public PGcircle(double x,
                 double y,
                 double r)
          
        Parameters:
               x - coordinate of centre
                y - coordinate of centre
                r - radius of circle

 public PGcircle(PGpoint c,
                 double r)
          
        Parameters:
                c - PGpoint describing the circle's centre
                r - radius of circle

 public PGcircle(String s) throws SQLException

        Parameters:
                s - definition of the circle in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

 public PGcircle()

          This constructor is used by the driver.
            
Methods   

 public void setValue(String s) throws SQLException

        Parameters:
                s - definition of the circle in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
            
        Returns:
                true if the two boxes are identical

        Overrides:
                equals in class PGobject

 public Object clone()

          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()

        Returns:
                the PGcircle in the syntax expected by postgresql
        
        Overrides:
                getValue in class PGobject

Class postgresql.geometric.PGline

java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.geometric.PGline

   public class PGline extends PGobject implements Serializable, 
Cloneable

   This implements a line consisting of two points. Currently line is 
not yet implemented in the backend, but this class ensures that when 
it's done were ready for it.

Variables
   
 public PGpoint point[]
     
          These are the two points.

Constructors

 public PGline(double x1,
               double y1,
               double x2,
               double y2)

        Parameters:
                x1 - coordinate for first point
                y1 - coordinate for first point
                x2 - coordinate for second point
                y2 - coordinate for second point

 public PGline(PGpoint p1,
               PGpoint p2)
     
        Parameters:
                p1 - first point
                p2 - second point

 public PGline(String s) throws SQLException
               
        Parameters:
                s - definition of the circle in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

 public PGline()

          reuired by the driver
               
Methods

 public void setValue(String s) throws SQLException

        Parameters:
                s - Definition of the line segment in PostgreSQL's 
syntax

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject
                
 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
               
        Returns:
                true if the two boxes are identical
   
        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()
   
        Returns:
                the PGline in the syntax expected by postgresql
        
        Overrides:
                getValue in class PGobject

Class postgresql.geometric.PGlseg
             
java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.geometric.PGlseg
          
   public class PGlseg extends PGobject implements Serializable, 
Cloneable
 
   This implements a lseg (line segment) consisting of two points

Variables

 public PGpoint point[]
           
          These are the two points.

Constructors
   
 public PGlseg(double x1,
               double y1,
               double x2,
               double y2)
     
        Parameters:

                x1 - coordinate for first point
                y1 - coordinate for first point
                x2 - coordinate for second point
                y2 - coordinate for second point

 public PGlseg(PGpoint p1,
               PGpoint p2)
           
        Parameters:
                p1 - first point
                p2 - second point
   
 public PGlseg(String s) throws SQLException

        Parameters:
                s - definition of the circle in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

 public PGlseg()

          reuired by the driver
               
Methods    
   
 public void setValue(String s) throws SQLException
   
        Parameters:
                s - Definition of the line segment in PostgreSQL's 
syntax

        Throws: SQLException
                on conversion failure
     
        Overrides:
                setValue in class PGobject
                
 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
               
        Returns:
                true if the two boxes are identical
   
        Overrides:
                equals in class PGobject
   
 public Object clone()

          This must be overidden to allow the object to be cloned

        Overrides:
               clone in class PGobject

 public String getValue()

        Returns:
                the PGlseg in the syntax expected by postgresql
        
        Overrides:
                getValue in class PGobject

Class postgresql.geometric.PGpath
                                
java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.geometric.PGpath
          
   public class PGpath extends PGobject implements Serializable, 
Cloneable
               
   This implements a path (a multiple segmented line, which may be 
closed)
           
Variables

 public boolean open
               
          True if the path is open, false if closed

 public PGpoint points[]

          The points defining this path

Constructors   

 public PGpath(PGpoint points[],
               boolean open)
          
        Parameters:
                points - the PGpoints that define the path
                open - True if the path is open, false if closed

 public PGpath()

          Required by the driver

 public PGpath(String s) throws SQLException

        Parameters:
                s - definition of the circle in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

Methods

 public void setValue(String s) throws SQLException
   
        Parameters:
                s - Definition of the path in PostgreSQL's syntax
           
        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with

        Returns:
                true if the two boxes are identical

        Overrides:
                equals in class PGobject

 public Object clone()

          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()

          This returns the polygon in the syntax expected by 
postgresql

        Overrides:
                getValue in class PGobject

 public boolean isOpen()

     This returns true if the path is open

 public boolean isClosed()

     This returns true if the path is closed

 public void closePath()

     Marks the path as closed

 public void openPath()

     Marks the path as open

Class postgresql.geometric.PGpoint
                                
java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.geometric.PGpoint
          
   public class PGpoint extends PGobject implements Serializable, 
Cloneable

   This implements a version of java.awt.Point, except it uses double 
to represent the coordinates.

   It maps to the point datatype in postgresql.

Variables

 public double x

          The X coordinate of the point

 public double y

          The Y coordinate of the point

Constructors

 public PGpoint(double x,
                double y)

        Parameters:
                x - coordinate
                y - coordinate

 public PGpoint(String value) throws SQLException
     
          This is called mainly from the other geometric types, when a 
point is imbeded within their definition.
             
        Parameters:
                value - Definition of this point in PostgreSQL's 
syntax
   
 public PGpoint()
          
          Required by the driver

Methods

 public void setValue(String s) throws SQLException

        Parameters:
                s - Definition of this point in PostgreSQL's syntax

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject
          
 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with

        Returns:
                true if the two boxes are identical

        Overrides:
                equals in class PGobject

 public Object clone()
                
          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class PGobject
          
 public String getValue()       
    
        Returns:
                the PGpoint in the syntax expected by postgresql

        Overrides:
                getValue in class PGobject
          
 public void translate(int x,
                       int y)

          Translate the point with the supplied amount.

        Parameters:
                x - integer amount to add on the x axis
                y - integer amount to add on the y axis

 public void translate(double x,
                       double y)
          
          Translate the point with the supplied amount.
 
        Parameters:
                x - double amount to add on the x axis
                y - double amount to add on the y axis

 public void move(int x,
                  int y)
                
          Moves the point to the supplied coordinates.

        Parameters:
                x - integer coordinate
                y - integer coordinate

public void move(double x,
                  double y)
          
          Moves the point to the supplied coordinates.

        Parameters:
                x - double coordinate
                y - double coordinate

 public void setLocation(int x,
                         int y)

          Moves the point to the supplied coordinates. refer to
          java.awt.Point for description of this

        Parameters:
                x - integer coordinate
                y - integer coordinate

        See Also:
                Point

 public void setLocation(Point p)

          Moves the point to the supplied java.awt.Point refer to
          java.awt.Point for description of this

        Parameters:
                p - Point to move to

        See Also:
                Point

Class postgresql.geometric.PGpolygon
                                
java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.geometric.PGpolygon

   public class PGpolygon extends PGobject implements Serializable, 
Cloneable
               
   This implements the polygon datatype within PostgreSQL.

Variables

 public PGpoint points[]

          The points defining the polygon
                                
Constructors

 public PGpolygon(PGpoint points[])

          Creates a polygon using an array of PGpoints

        Parameters:
                points - the points defining the polygon

 public PGpolygon(String s) throws SQLException
                 
        Parameters:
                s - definition of the circle in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

 public PGpolygon()

          Required by the driver

Methods

 public void setValue(String s) throws SQLException

        Parameters:
                s - Definition of the polygon in PostgreSQL's syntax

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)
     
        Parameters:
                obj - Object to compare with
                                
        Returns:
                true if the two boxes are identical

        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class PGobject
                 
 public String getValue()

        Returns:
                the PGpolygon in the syntax expected by postgresql

        Overrides:
                getValue in class PGobject

Large Objects

Large objects are supported in the standard JDBC specification. 
However, that interface is limited, and the api provided by PostgreSQL 
allows for random access to the objects contents, as if it was a local 
file.

The postgresql.largeobject package profides to Java the libpq C 
interface's large object API. It consists of two classes, 
LargeObjectManager, which deals with creating, opening and deleting 
large obejects, and LargeObject which deals with an individual object.

Class postgresql.largeobject.LargeObject

java.lang.Object
   |
   +----postgresql.largeobject.LargeObject

public class LargeObject extends Object

This class implements the large object interface to postgresql.

   It provides the basic methods required to run the interface, plus a 
pair of methods that provide InputStream and OutputStream classes for 
this object.

   Normally, client code would use the getAsciiStream, 
getBinaryStream, or getUnicodeStream methods in ResultSet, or 
setAsciiStream, setBinaryStream, or setUnicodeStream methods in 
PreparedStatement to access Large Objects.

   However, sometimes lower level access to Large Objects are 
required, that are not supported by the JDBC specification.

   Refer to postgresql.largeobject.LargeObjectManager on how to gain 
access to a Large Object, or how to create one.

   See Also:
          LargeObjectManager

Variables

 public static final int SEEK_SET

          Indicates a seek from the begining of a file

 public static final int SEEK_CUR

          Indicates a seek from the current position

 public static final int SEEK_END

          Indicates a seek from the end of a file

Methods

 public int getOID()

        Returns:
                the OID of this LargeObject

 public void close() throws SQLException

          This method closes the object. You must not call methods in 
this object after this is called.

    Throws: SQLException
                if a database-access error occurs.

 public byte[] read(int len) throws SQLException

          Reads some data from the object, and return as a byte[] 
array

        Parameters:
                len - number of bytes to read

        Returns:
                byte[] array containing data read

        Throws: SQLException
                if a database-access error occurs.

 public void read(byte buf[],
                  int off,
                  int len) throws SQLException

          Reads some data from the object into an existing array

        Parameters:
                buf - destination array
                off - offset within array
                len - number of bytes to read

        Throws: SQLException
                if a database-access error occurs.

 public void write(byte buf[]) throws SQLException

          Writes an array to the object


        Parameters:
                buf - array to write

        Throws: SQLException
                if a database-access error occurs.

 public void write(byte buf[],
                   int off,
                   int len) throws SQLException

          Writes some data from an array to the object

        Parameters:
                buf - destination array
                off - offset within array
                len - number of bytes to write

        Throws: SQLException
                if a database-access error occurs.

 public void seek(int pos,
                  int ref) throws SQLException

          Sets the current position within the object.

          This is similar to the fseek() call in the standard C 
library.It allows you to have random access to the large object.

        Parameters:
                pos - position within object
                ref - Either SEEK_SET, SEEK_CUR or SEEK_END
        Throws: SQLException
                if a database-access error occurs.

 public void seek(int pos) throws SQLException

          Sets the current position within the object.

          This is similar to the fseek() call in the standard C 
library.It allows you to have random access to the large object.

        Parameters:
                pos - position within object from begining

        Throws: SQLException
                if a database-access error occurs.

 public int tell() throws SQLException

        Returns:
                the current position within the object

        Throws: SQLException
                if a database-access error occurs.

 public int size() throws SQLException

          This method is inefficient, as the only way to find out the 
size of the object is to seek to the end, record the current position, 
then return to the original position.

          A better method will be found in the future.

        Returns:
                the size of the large object

        Throws: SQLException
                if a database-access error occurs.

 public InputStream getInputStream() throws SQLException

          Returns an InputStream from this object.

          This InputStream can then be used in any method that 
requires an InputStream.

        Throws: SQLException
                if a database-access error occurs.

 public OutputStream getOutputStream() throws SQLException

          Returns an OutputStream to this object

          This OutputStream can then be used in any method that 
requires an OutputStream.

        Throws: SQLException
                if a database-access error occurs.

Class postgresql.largeobject.LargeObjectManager
                                
java.lang.Object
   |
   +----postgresql.largeobject.LargeObjectManager

public class LargeObjectManager extends Object

This class implements the large object interface to postgresql.
        
   It provides methods that allow client code to create, open and 
delete large objects from the database. When opening an object, an 
instance of postgresql.largeobject.LargeObject is returned, and its 
methods then allow access to the object.

This class can only be created by postgresql.Connection

To get access to this class, use the following segment of code:

 import postgresql.largeobject.*;
 Connection  conn;
 LargeObjectManager lobj;
 ... code that opens a connection ...
 lobj = ((postgresql.Connection)myconn).getLargeObjectAPI();

Normally, client code would use the getAsciiStream, getBinaryStream, 
or getUnicodeStream methods in ResultSet, or setAsciiStream, 
setBinaryStream, or setUnicodeStream methods in PreparedStatement to 
access Large Objects.

   However, sometimes lower level access to Large Objects are 
required, that are not supported by the JDBC specification.

   Refer to postgresql.largeobject.LargeObject on how to manipulate 
the contents of a Large Object.

   See Also:
          LargeObject

Variables

 public static final int WRITE

          This mode indicates we want to write to an object

 public static final int READ

          This mode indicates we want to read an object

 public static final int READWRITE

          This mode is the default. It indicates we want read and 
write access to a large object

Methods

 public LargeObject open(int oid) throws SQLException
          
          This opens an existing large object, based on its OID. This
          method assumes that READ and WRITE access is required (the 
default).

        Parameters:
                oid - of large object

        Returns:
                LargeObject instance providing access to the object

        Throws: SQLException
                on error

 public LargeObject open(int oid,
                         int mode) throws SQLException
          
          This opens an existing large object, based on its OID
  
        Parameters:
                oid - of large object
                mode - mode of open

        Returns:
                LargeObject instance providing access to the object

        Throws: SQLException
                on error

 public int create() throws SQLException

          This creates a large object, returning its OID.

          It defaults to READWRITE for the new object's attributes.

        Returns:
                oid of new object

        Throws: SQLException
                on error

 public int create(int mode) throws SQLException

          This creates a large object, returning its OID

        Parameters:
                mode - a bitmask describing different attributes of 
the
                new object

        Returns:
                oid of new object

        Throws: SQLException
                on error

 public void delete(int oid) throws SQLException
          
          This deletes a large object.
          
        Parameters:
                oid - describing object to delete

        Throws: SQLException
                on error

 public void unlink(int oid) throws SQLException

          This deletes a large object.

          It is identical to the delete method, and is supplied as the 
C API uses unlink.

        Parameters:
                oid - describing object to delete

        Throws: SQLException
                on error

Object Serialisation
PostgreSQL is not a normal SQL Database. It is far more extensible 
than most other databases, and does support Object Oriented features 
that are unique to it. 

One of the consequences of this, is that you can have one table refer 
to a row in another table. For example:

test=> create table users (username name,fullname text);
CREATE
test=> create table server (servername name,adminuser users);
CREATE
test=> insert into users values ('peter','Peter Mount');
INSERT 2610132 1
test=> insert into server values ('maidast',2610132::users);
INSERT 2610133 1
test=> select * from users;
username|fullname      
--------+--------------
peter   |Peter Mount   
(1 row)

test=> select * from server;
servername|adminuser
----------+---------
maidast   |  2610132
(1 row)

Ok, the above example shows that we can use a table name as a field, 
and the row's oid value is stored in that field.

What does this have to do with Java?

In Java, you can store an object to a Stream as long as it's class 
implements the java.io.Serializable interface. This process, known as 
Object Serialization, can be used to store complex objects into the 
database.

Now, under JDBC, you would have to use a LargeObject to store them. 
However, you cannot perform queries on those objects.

What the postgresql.util.Serialize class does, is provide a means of 
storing an object as a table, and to retrieve that object from a 
table. In most cases, you would not need to access this class direct, 
but you would use the PreparedStatement.setObject() and 
ResultSet.getObject() methods. Those methods will check the objects 
class name against the table's in the database. If a match is found, 
it assumes that the object is a Serialized object, and retrieves it 
from that table. As it does so, if the object contains other 
serialized objects, then it recurses down the tree.

Sound's complicated? In fact, it's simpler than what I wrote - it's 
just difficult to explain.

The only time you would access this class, is to use the create() 
methods. These are not used by the driver, but issue one or more 
"create table" statements to the database, based on a Java Object or 
Class that you want to serialize.

Oh, one last thing. If your object contains a line like:

     public int oid;

then, when the object is retrieved from the table, it is set to the 
oid within the table. Then, if the object is modified, and re-
serialized, the existing entry is updated.

If the oid variable is not present, then when the object is 
serialized, it is always inserted into the table, and any existing 
entry in the table is preserved.

Setting oid to 0 before serialization, will also cause the object to 
be inserted. This enables an object to be duplicated in the database.

Class postgresql.util.Serialize

java.lang.Object
   |
   +----postgresql.util.Serialize

   public class Serialize extends Object

   This class uses PostgreSQL's object oriented features to store Java 
Objects. It does this by mapping a Java Class name to a table in the 
database. Each entry in this new table then represents a Serialized 
instance of this class. As each entry has an OID (Object IDentifier), 
this OID can be included in another table. This is too complex to show 
here, and will be documented in the main documents in more detail.

Constructors

 public Serialize(Connection c,
                  String type) throws SQLException

          This creates an instance that can be used to serialize 
ordeserialize a Java object from a PostgreSQL table.

Methods

 public Object fetch(int oid) throws SQLException

          This fetches an object from a table, given it's OID

        Parameters:
                oid - The oid of the object

        Returns:
                Object relating to oid

        Throws: SQLException
                on error

 public int store(Object o) throws SQLException

          This stores an object into a table, returning it's OID.

          If the object has an int called OID, and it is > 0, then 
that value is used for the OID, and the table will be updated. If the 
value of OID is 0, then a new row will be created, and the value of 
OID will be set in the object. This enables an object's value in the 
database to be updateable. If the object has no int called OID, then 
the object is stored. However if the object is later retrieved, 
amended and stored again, it's new state will be appended to the 
table, and will not overwrite the old entries.

        Parameters:
                o - Object to store (must implement Serializable)

        Returns:
                oid of stored object

        Throws: SQLException
                on error
 
 public static void create(Connection con,
                           Object o) throws SQLException

          This method is not used by the driver, but it creates a 
table, given a Serializable Java Object. It should be used before 
serializing any objects.

        Parameters:
                c - Connection to database
                o - Object to base table on

        Throws: SQLException
                on error

                   Returns:
                Object relating to oid

        Throws: SQLException
                on error

 public int store(Object o) throws SQLException

          This stores an object into a table, returning it's OID.

          If the object has an int called OID, and it is > 0, then 
that value is used for the OID, and the table will be updated. If the 
value of OID is 0, then a new row will be created, and the value of 
OID will be set in the object. This enables an object's value in the 
database to be updateable. If the object has no int called OID, then 
the object is stored. However if the object is later retrieved, 
amended and stored again, it's new state will be appended to the 
table, and will not overwrite the old entries.

        Parameters:
                o - Object to store (must implement Serializable)

        Returns:
                oid of stored object

        Throws: SQLException
                on error
 
 public static void create(Connection con,
                           Object o) throws SQLException

          This method is not used by the driver, but it creates a 
table, given a Serializable Java Object. It should be used before 
serializing any objects.

        Parameters:
                c - Connection to database
                o - Object to base table on

        Throws: SQLException
                on error
                
 public static void create(Connection con,
                           Class c) throws SQLException

          This method is not used by the driver, but it creates a 
table, given a Serializable Java Object. It should be used before 
serializing any objects.

        Parameters:
                c - Connection to database
                o - Class to base table on

        Throws: SQLException
                on error

 public static String toPostgreSQL(String name) throws SQLException
          
          This converts a Java Class name to a postgresql table, by
          replacing . with _

          Because of this, a Class name may not have _ in the name.

          Another limitation, is that the entire class name (including
          packages) cannot be longer than 31 characters (a limit 
forced by PostgreSQL).

        Parameters:
                name - Class name

        Returns:
                PostgreSQL table name

        Throws: SQLException
                on error
          
 public static String toClassName(String name) throws SQLException

          This converts a postgresql table to a Java Class name, by
          replacing _ with .

        Parameters:
                name - PostgreSQL table name
  
        Returns:
                Class name

        Throws: SQLException
                on error

Utility Classes

The postgresql.util package contains classes used by the internals of 
the main driver, and the other extensions.

Class postgresql.util.PGmoney
                                
java.lang.Object
   |
   +----postgresql.util.PGobject
           |
           +----postgresql.util.PGmoney

   public class PGmoney extends PGobject implements Serializable, 
Cloneable
               
   This implements a class that handles the PostgreSQL money type

Variables

 public double val
                                
          The value of the field

Constructors
           
 public PGmoney(double value)
   
        Parameters:
                value - of field
               
 public PGmoney(String value) throws SQLException
   
          This is called mainly from the other geometric types, when a 
point is imbeded within their definition.

        Parameters:
                value - Definition of this point in PostgreSQL's 
syntax

 public PGmoney()

          Required by the driver

Methods

 public void setValue(String s) throws SQLException

        Parameters:
                s - Definition of this point in PostgreSQL's syntax

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
                                
        Returns:
                true if the two boxes are identical

        Overrides:
                equals in class PGobject

 public Object clone()
                
          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()

        Returns:
                the PGpoint in the syntax expected by postgresql

        Overrides:
                getValue in class PGobject

Class postgresql.util.PGobject

java.lang.Object
   |
   +----postgresql.util.PGobject

   public class PGobject extends Object implements Serializable, 
Cloneable
               
   This class is used to describe data types that are unknown by
     JDBC 
Standard.
    A call to postgresql.Connection permits a class that extends this 
class to be associated with a named type. This is how the 
postgresql.geometric package operates.
    ResultSet.getObject() will return this class for any type that is 
not recognised on having it's own handler. Because of this, any 
postgresql data type is supported.

Constructors

 public PGobject()

          This is called by postgresql.Connection.getObject() to 
create the object.

Methods

 public final void setType(String type)

          This method sets the type of this object.

          It should not be extended by subclasses, hence its final

        Parameters:
                type - a string describing the type of the object

 public void setValue(String value) throws SQLException

          This method sets the value of this object. It must be 
overidden.

        Parameters:
                value - a string representation of the value of the
                object

        Throws: SQLException
                thrown if value is invalid for this type
    
 public final String getType()

          As this cannot change during the life of the object, it's 
final.

        Returns:
                the type name of this object

 public String getValue()

          This must be overidden, to return the value of the object, 
in the form required by postgresql.

        Returns:
                the value of this object

 public boolean equals(Object obj)

          This must be overidden to allow comparisons of objects

        Parameters:
                obj - Object to compare with

        Returns:
                true if the two boxes are identical

        Overrides:
                equals in class Object

 public Object clone()

          This must be overidden to allow the object to be cloned

        Overrides:
                clone in class Object

 public String toString()

          This is defined here, so user code need not overide it.
          
        Returns:
                the value of this object, in the syntax expected by 
postgresql

        Overrides:
                toString in class Object

Class postgresql.util.PGtokenizer

java.lang.Object
   |
   +----postgresql.util.PGtokenizer

   public class PGtokenizer extends Object

   This class is used to tokenize the text output of postgres.

   We could have used StringTokenizer to do this, however, we needed 
to handle nesting of '(' ')' '[' ']' '<' and '>' as these are used by 
the geometric data types.

   It's mainly used by the geometric classes, but is useful in parsing 
any output from custom data types output from postgresql.
                 
   See Also:
          PGbox, PGcircle, PGlseg, PGpath, PGpoint, PGpolygon
          
Constructors

 public PGtokenizer(String string,
                    char delim)

          Create a tokeniser.

        Parameters:
                string - containing tokens
                delim - single character to split the tokens

Methods
        
 public int tokenize(String string,
                     char delim)

          This resets this tokenizer with a new string and/or 
delimiter.

        Parameters:
                string - containing tokens
                delim - single character to split the tokens

 public int getSize()

        Returns:
                the number of tokens available

 public String getToken(int n)

        Parameters:
                n - Token number ( 0 ... getSize()-1 )

        Returns:
                The token value

 public PGtokenizer tokenizeToken(int n,
                                  char delim)

          This returns a new tokenizer based on one of our tokens. The 
geometric datatypes use this to process nested tokens (usually 
PGpoint).

        Parameters:
                n - Token number ( 0 ... getSize()-1 )
                delim - The delimiter to use

        Returns:
                A new instance of PGtokenizer based on the token

 public static String remove(String s,
                             String l,
                             String t)

          This removes the lead/trailing strings from a string

        Parameters:
                s - Source string
                l - Leading string to remove
                t - Trailing string to remove
                
        Returns:
                String without the lead/trailing strings

 public void remove(String l,
                    String t)

          This removes the lead/trailing strings from all tokens

        Parameters:
                l - Leading string to remove
                t - Trailing string to remove

 public static String removePara(String s)

          Removes ( and ) from the beginning and end of a string

        Parameters:
                s - String to remove from

        Returns:
                String without the ( or )

 public void removePara()

          Removes ( and ) from the beginning and end of all tokens

        Returns:
                String without the ( or )

 public static String removeBox(String s)
   
          Removes [ and ] from the beginning and end of a string

        Parameters:
                s - String to remove from
   
        Returns:
                String without the [ or ]

 public void removeBox()

          Removes [ and ] from the beginning and end of all tokens

        Returns:
                String without the [ or ]

 public static String removeAngle(String s)

          Removes < and > from the beginning and end of a string

        Parameters:
                s - String to remove from

        Returns:
                String without the < or >

 public void removeAngle()

          Removes < and > from the beginning and end of all tokens

        Returns:
                String without the < or >

Class postgresql.util.Serialize

This was documented earlier under Object Serialisation.

Class postgresql.util.UnixCrypt
              
java.lang.Object
   |
   +----postgresql.util.UnixCrypt

   public class UnixCrypt extends Object

   This class provides us with the ability to encrypt passwords when 
sent over the network stream

   Contains static methods to encrypt and compare passwords with Unix 
encrypted passwords.

   See John Dumas's Java Crypt page for the original source.

   http://www.zeh.com/local/jfd/crypt.html

Methods

 public static final String crypt(String salt,
                                  String original)

          Encrypt a password given the cleartext password and a 
"salt".
   
        Parameters:
                salt - A two-character string representing the salt 
used
                to iterate the encryption engine in lots of different
                ways. If you are generating a new encryption then this
                value should be randomised.
                original - The password to be encrypted.

        Returns:
                A string consisting of the 2-character salt followed 
by
                the encrypted password.
              
 public static final String crypt(String original)

          Encrypt a password given the cleartext password. This method 
generates a random salt using the 'java.util.Random' class.

        Parameters:
                original - The password to be encrypted.
   
        Returns: 
                A string consisting of the 2-character salt followed 
by
                the encrypted password.
               
 public static final boolean matches(String encryptedPassword,
                                     String enteredPassword)
                 
          Check that enteredPassword encrypts to encryptedPassword.
               
        Parameters:
                encryptedPassword - The encryptedPassword. The first 
two characters are assumed to be the salt. This string would be the 
same as one found in a Unix /etc/passwd file.
                enteredPassword - The password as entered by the user 
(or otherwise aquired).

        Returns:
                true if the password should be considered correct.

Using the driver in a multi Threaded or Servlet environment

A problem with many JDBC drivers, is that only one thread can use a 
Connection at any one time - otherwise a thread could send a query 
while another one is receiving results, and this would be a bad thing 
for the database engine.

PostgreSQL 6.4, brings thread safety to the entire driver. Standard 
JDBC was thread safe in 6.3.x, but the Fastpath
     API wasn't.

So, if your application uses multiple threads (which most decent ones 
would), then you don't have to worry about complex schemes to ensure 
only one uses the database at any time.

If a thread attempts to use the connection while another is using it, 
it will wait until the other thread has finished it's current 
operation.

If it's a standard SQL statement, then the operation is sending the 
statement, and retrieving any ResultSet (in full).

If it's a Fastpath call (ie: reading a block from a LargeObject), then 
it's the time to send, and retrieve that block.

This is fine for applications & applets, but can cause a performance 
problem with servlets.

With servlets, you can have a heavy load on the connection. If you 
have several threads performing queries, then each one will pause, 
which may not be what you are after.

To solve this, you would be advised to create a pool of Connections.

When ever a thread needs to use the database, it asks a manager class 
for a Connection. It hands a free connection to the thread, and marks 
it as busy. If a free connection is not available, it opens one.

Once the thread has finished with it, it returns it to the manager, 
who can then either close it, or add it to the pool. The manager would 
also check that the connection is still alive, and remove it from the 
pool if it's dead.

So, with servlets, it's up to you to use either a single connection, 
or a pool. The plus side for a pool is that threads will not be hit by 
the bottle neck caused by a single network connection. The down side, 
is that it increases the load on the server, as a backend is created 
for each Connection.

It's up to you, and your applications requirements.
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