PostgreSQL Extensions to the JDBC API

PostgreSQL 7.3.4 Documentation
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# 5.7. PostgreSQL Extensions to the JDBC API

PostgreSQL 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. 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.

## 5.7.1. 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();

### 5.7.1.1. Class `org.postgresql.PGConnection`

    public class PGConnection

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

#### 5.7.1.1.1. Methods

-     public Fastpath getFastpathAPI() throws SQLException

  This returns the Fastpath 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 backend.

  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`.

### 5.7.1.2. 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 backend. 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 backend function.

See Also: `FastpathFastpathArg`, `LargeObject`

#### 5.7.1.2.1. 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

-     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 preferred method to call, as function id's can/may change between versions of the backend. 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 fastpath

  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.

### 5.7.1.3. Class `org.postgresql.fastpath.FastpathArg`

    public class FastpathArg extends Object

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

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 `org.postgresql.LargeObject` package.

See Also: `Fastpath`, `LargeObjectManager`, `LargeObject`

#### 5.7.1.3.1. 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.

## 5.7.2. 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 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 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

## 5.7.3. 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.

### 5.7.3.1. 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`

#### 5.7.3.1.1. 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

#### 5.7.3.1.2. 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

### 5.7.3.2. 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.

#### 5.7.3.2.1. 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.

#### 5.7.3.2.2. 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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