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.
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();
public class PGConnection
These are the extra methods used to gain access to PostgreSQL's extensions.
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.
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
public Object fastpath(int fnid,
boolean resulttype,
FastpathArg args[]) throws SQLExceptionSend 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 SQLExceptionSend 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 SQLExceptionThis 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 SQLExceptionThis 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.
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
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:
source array
offset within array
length of data to include
public FastpathArg(String s)
Constructs an argument that consists of a String.
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 PGobjectLarge 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.
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
Indicates a seek from the beginning of a file
Indicates a seek from the current position
Indicates a seek from the end of a file
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 SQLExceptionReads some data from the object into an existing array
Parameters:
destination array
offset within array
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 SQLExceptionWrites some data from an array to the object
Parameters:
destination array
offset within array
number of bytes to write
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.
This mode indicates we want to write to an object.
This mode indicates we want to read an object.
This mode is the default. It indicates we want read and write access to a large object.
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 SQLExceptionThis 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".