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31.8. PostgreSQL Extensions to the JDBC API

PostgreSQL is an extensible database system. You can add your own functions to the server, which can then be called from queries, or even add your own data types. As these are facilities unique to PostgreSQL, 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.

31.8.1. Accessing the Extensions

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

Connection db = Driver.getConnection(url, username, password);
// ...
// later on
Fastpath fp = ((org.postgresql.PGConnection)db).getFastpathAPI();

31.8.1.1. Class org.postgresql.PGConnection

public class PGConnection 

These are the extra methods used to gain access to PostgreSQL's extensions.

31.8.1.1.1. Methods

  • public Fastpath getFastpathAPI() throws SQLException
    

    This returns the fast-path API for the current connection. It is primarily used by the Large Object API.

    The best way to use this is as follows:

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

    where myconn is an open Connection to PostgreSQL.

    Returns: Fastpath object allowing access to functions on the PostgreSQL server.

    Throws: SQLException by Fastpath when initializing for first time

  • public LargeObjectManager getLargeObjectAPI() throws SQLException
    

    This returns the Large Object API for the current connection.

    The best way to use this is as follows:

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

    where myconn is an open Connection to PostgreSQL.

    Returns: LargeObject object that implements the API

    Throws: SQLException by LargeObject when initializing 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.

    The best way to use this is as follows:

     ...
    ((org.postgresql.PGConnection)myconn).addDataType("mytype","my.class.name");
     ...
    

    where myconn is an open Connection to PostgreSQL. The handling class must extend org.postgresql.util.PGobject.

31.8.1.2. Class org.postgresql.Fastpath

public class Fastpath extends Object

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

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

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

import org.postgresql.fastpath.*;

Then, in your code, you need to get a FastPath object:

Fastpath fp = ((org.postgresql.PGConnection)conn).getFastpathAPI();

This will return an instance associated with the database connection that you can use to issue commands. The casing of Connection to org.postgresql.PGConnection is required, as the getFastpathAPI() is an extension method, not part of JDBC. Once you have a Fastpath instance, you can use the fastpath() methods to execute a server function.

See Also: FastpathFastpathArg, LargeObject

31.8.1.2.1. Methods

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

    Send a function call to the PostgreSQL server.

    Parameters: fnid - Function id resulttype - True if the result is an integer, false for other results args - FastpathArguments to pass to fast-path call

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

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

    Send a function call to the PostgreSQL server 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 preferred method to call, as function id's can/may change between versions of the server. For an example of how this works, refer to org.postgresql.LargeObject

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

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

    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 look-up 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.

  • 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.

    Important: Remember to close() the ResultSet after calling this!

    Implementation note about function name look-ups: 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 org.postgresql.LargeObject class performs a query upon its start-up, and passes the returned ResultSet to the addFunctions() method here. Once this has been done, the Large Object API refers to the functions by name.

    Do not think that manually converting them to the OIDs 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.

    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.

31.8.1.3. Class org.postgresql.fastpath.FastpathArg

public class FastpathArg extends Object

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

Each fast-path 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 org.postgresql.LargeObject package.

See Also: Fastpath, LargeObjectManager, LargeObject

31.8.1.3.1. 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.

31.8.2. Geometric Data Types

PostgreSQL has a set of data types that can store geometric features into a table. These include single points, lines, and polygons. We support these types in Java with the org.postgresql.geometric package. It contains classes that extend the org.postgresql.util.PGobject class. Refer to that class for details on how to implement your own data type handlers.

Class org.postgresql.geometric.PGbox

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

   public class PGbox extends PGobject implements Serializable, 
Cloneable

   This represents the box data type 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 
overridden, 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 overridden 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 org.postgresql.geometric.PGcircle

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

Variables

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

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

 public PGcircle(PGpoint c,
                 double r)
          
        Parameters:
                c - PGpoint describing the circle's center
                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 circles are identical

        Overrides:
                equals in class PGobject

 public Object clone()

          This must be overridden 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 org.postgresql.geometric.PGline

java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.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 server, 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 line in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

 public PGline()

          required 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 lines are identical
   
        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overridden 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 org.postgresql.geometric.PGlseg
             
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.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 line segment in PostgreSQL's syntax.

        Throws: SQLException
                on conversion failure

 public PGlseg()

          required 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 line segments are identical
   
        Overrides:
                equals in class PGobject
   
 public Object clone()

          This must be overridden 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 org.postgresql.geometric.PGpath
                                
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGpath
          
   public class PGpath extends PGobject implements Serializable, 
Cloneable
               
   This implements a path (a multiply 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 path 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 pathes are identical

        Overrides:
                equals in class PGobject

 public Object clone()

          This must be overridden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()

          This returns the path 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 org.postgresql.geometric.PGpoint
                                
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.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 data type 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 embedded 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 points are identical

        Overrides:
                equals in class PGobject

 public Object clone()
                
          This must be overridden 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 org.postgresql.geometric.PGpolygon
                                
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGpolygon

   public class PGpolygon extends PGobject implements Serializable, 
Cloneable
               
   This implements the polygon data type 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 polygon 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 polygons are identical

        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overridden 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

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

31.8.3.1. Class org.postgresql.largeobject.LargeObject

public class LargeObject extends Object

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

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 methods in BLOB to access large objects.

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

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

See Also: LargeObjectManager

31.8.3.1.1. Variables

public static final int SEEK_SET

Indicates a seek from the beginning 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

31.8.3.1.2. 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.

  • public byte[] read(int len) throws SQLException
    

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

  • public int 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

  • public void write(byte buf[]) throws SQLException
    

    Writes an array to the object

  • 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

31.8.3.2. Class org.postgresql.largeobject.LargeObjectManager

                                
public class LargeObjectManager extends Object

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

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 org.postgresql.largeobject.LargeObject is returned, and its methods then allow access to the object.

This class can only be created by org.postgresql.PGConnection. To get access to this class, use the following segment of code:

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

Normally, client code would use the BLOB methods to access large objects. However, sometimes lower level access to Large Objects is required, that is not supported by the JDBC specification.

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

31.8.3.2.1. 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.

31.8.3.2.2. 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).

  • public LargeObject open(int oid,
                            int mode) throws SQLException
    

    This opens an existing large object, based on its OID, and allows setting the access mode.

  • public int create() throws SQLException
    

    This creates a large object, returning its OID. It defaults to READWRITE for the new object's attributes.

  • public int create(int mode) throws SQLException
    

    This creates a large object, returning its OID, and sets the access mode.

  • public void delete(int oid) throws SQLException
    

    This deletes a large object.

  • 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".

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