<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/Attic/jdbc.sgml,v 1.28 2001/11/21 05:53:41 thomas Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/Attic/jdbc.sgml,v 1.29 2001/11/26 05:57:57 barry Exp $
-->
<chapter id="jdbc">
<para>
Any time you want to issue <acronym>SQL</acronym> statements to
- the database, you require a <classname>Statement</classname>
- instance. Once you have a <classname>Statement</classname>, you
- can use the <function>executeQuery()</function> method to issue a
+ the database, you require a <classname>Statement</classname> or
+ <classname>PreparedStatement</classname> instance. Once you have
+ a <classname>Statement</classname> or <classname>PreparedStatement
+ </classname>, you
+ can use issue a
query. This will return a <classname>ResultSet</classname>
instance, which contains the entire result. <xref
linkend="jdbc-query-example"> illustrates this process.
<title>Processing a Simple Query in <acronym>JDCB</acronym></title>
<para>
- This example with issue a simple query and print out the first
- column of each row.
+ This example will issue a simple query and print out the first
+ column of each row using a <classname>Statement</classname>.
<programlisting>
Statement st = db.createStatement();
-ResultSet rs = st.executeQuery("SELECT * FROM mytable");
+ResultSet rs = st.executeQuery("SELECT * FROM mytable where columnfoo = 500");
+while(rs.next()) {
+ System.out.print("Column 1 returned ");
+ System.out.println(rs.getString(1));
+}
+rs.close();
+st.close();
+</programlisting>
+ </para>
+
+ <para>
+ This example will issues the same query as before using
+ a <classname>PreparedStatement</classname>
+ and a bind value in the query.
+<programlisting>
+int foovalue = 500;
+PreparedStatement st = db.prepareStatement("SELECT * FROM mytable where columnfoo = ?");
+st.setInt(1, foovalue);
+ResultSet rs = st.executeQuery();
while(rs.next()) {
System.out.print("Column 1 returned ");
System.out.println(rs.getString(1));
</example>
<sect2>
- <title>Using the <classname>Statement</classname> Interface</title>
+ <title>Using the <classname>Statement</classname> or <classname>
+ PreparedStatement</classname> Interface</title>
<para>
The following must be considered when using the
open the connection and use it for the connection's
lifetime. But you have to remember that only one
<classname>ResultSet</classname> can exist per
- <classname>Statement</classname>.
+ <classname>Statement</classname> at a given time.
</para>
</listitem>
thinking of using threads, as it covers some important points.
</para>
</listitem>
+
+ <listitem>
+ <para>
+ When you are done using the <classname>Statement</classname>
+ you should close the <classname>Statement</classname>.
+ </para>
+ </listitem>
</itemizedlist>
</para>
</sect2>
<title>Performing Updates</title>
<para>
- To perform an update (or any other <acronym>SQL</acronym>
- statement that does not return a result), you simply use the
- <function>executeUpdate()</function> method:
+ To change data (perform an insert, update, or delete)
+ you use the <function>executeUpdate()</function> method.
+ <function>executeUpdate()</function> is similar to the
+ <function>executeQuery()</function> used to issue a select,
+ however it doesn't return a <classname>ResultSet</classname>,
+ instead it returns the number of records affected by the insert,
+ update, or delete statement.
+ </para>
+ <para>
+ This example will issue a simple delete and print out the number
+ of rows deleted.
<programlisting>
-st.executeUpdate("CREATE TABLE basic (a int, b int)");
+int foovalue = 500;
+PreparedStatement st = db.prepareStatement("DELETE FROM mytable where columnfoo = ?");
+st.setInt(1, foovalue);
+int rowsDeleted = st.executeUpdate();
+System.out.println(rowsDeleted + " rows deleted");
+st.close();
</programlisting>
</para>
</sect1>
- <sect1 id="jdbc-lo">
- <title>Using Large Objects</title>
+ <sect1 id="jdbc-ddl">
+ <title>Creating and Modifying Database Objects</title>
+
+ <para>
+ To create, modify or drop a database object like a table or view
+ you use the <function>execute()</function> method.
+ <function>execute</function> is similar to the
+ <function>executeQuery()</function> used to issue a select,
+ however it doesn't return a result.
+ </para>
+
+ <para>
+ This example will drop a table.
+<programlisting>
+Statement st = db.createStatement();
+ResultSet rs = st.executeQuery("DROP TABLE mytable");
+st.close();
+</programlisting>
+ </para>
+ </sect1>
+
+ <sect1 id="jdbc-binary-data">
+ <title>Storing Binary Data</title>
+
+ <para>
+ <application>PostgreSQL</application> provides two distinct way to
+ store binary data. Binary data can be stored in a table using
+ <applicaiton>PostgreSQL's</application> binary datatype
+ <type>bytea</type>, or by using the <firstterm>Large Object</firstterm>
+ feature which stores the binary data in a separate table in a special
+ format, and refers to from your own tables by an <type>OID</type> value.
+ </para>
+
+ <para>
+ In order to determine which method is appropriate you
+ need to understand the limitations of each method. The
+ <type>bytea</type> datatype is not well suited for storing very
+ large amounts of binary data. While a column of type
+ <type>bytea</bytea> can hold upto 1Gig of binary data, it would
+ require a huge amount of memory (<acronym>RAM</acronym>) to
+ process such a large value. The Large Object method for
+ storing binary data is better suited to storing very large values,
+ but it has its own limitations. Specifically deleting a row
+ that contains a Large Object does not delete the Large Object.
+ Deleting the Large Object is a separate operation that needs to
+ be performed. Large Objects also have some security
+ issues since anyone connected to the database case view
+ and/or modify any Large Object, even if they don't have
+ permissions to view/update the row containing the Large Object.
+ </para>
+
+ <para>
+ 7.2 is the first release that the <acronym>JDBC</acronym> Driver
+ supports the <type>bytea</type> datatype. The introduction of
+ this functionality in 7.2 has introduced a change in behavior
+ as compared to previous releases. In 7.2 the methods
+ <function>getBytes()</function>, <function>setBytes()</function>,
+ <function>getBinaryStream()</function>, and
+ <function>setBinaryStream()</function> operate on
+ the <type>bytea</type> datatype. In 7.1 these methods operated
+ on the <type>OID</type> datatype associated with Large Objects.
+ It is possible to revert the driver back to the old 7.1 behavior
+ by setting the <parameter>compatible</parameter> property on
+ the <classname>Connection</classname> to a value of
+ <literal>7.1</literal>
+ </para>
<para>
- In <application>PostgreSQL</application>, <firstterm>Large
- Objects</firstterm> (also known as <acronym>BLOB</acronym>s) are
- used to hold data in the database that cannot be stored in a normal
- SQL table. They are stored in a separate table in a special format,
- and are referred to from your own tables by an OID value.
+ To use the <type>bytea</type> datatype you should simply use
+ the <function>getBytes()</function>, <function>setBytes()</function>,
+ <function>getBinaryStream()</function>, or
+ <function>setBinaryStream()</function> methods.
+ </para>
+
+ <para>
+ To use the Large Object functionality you can use either the
+ <classname>LargeObject</classname> <acronym>API</acronym>
+ provided by the <application>PostgreSQL</applicaiton>
+ <acronym>JDBC</acronym> Driver, or by using the
+ <function>getBLOB()</function> and <function>setBLOB()</function>
+ methods.
</para>
<important>
<para>
- For <productname>PostgreSQL</productname>, you must access Large
+ For <application>PostgreSQL</application>, you must access Large
Objects within an <acronym>SQL</acronym> transaction. You would
open a transaction by using the
<function>setAutoCommit()</function> method with an input
- parameter of <literal>false</literal>:
-<programlisting>
-Connection mycon;
-...
-mycon.setAutoCommit(false);
-... // now use Large Objects
-</programlisting>
+ parameter of <literal>false</literal>.
</para>
</important>
- <para>
- There are two methods of using Large Objects. The first is the
- standard <acronym>JDBC</acronym> way, and is documented here. The
- other, uses <productname>PostgreSQL</productname> extensions to
- the <acronym>API</acronym>, which presents the <application>libpq</application> large object
- <acronym>API</acronym> to Java, providing even better access to
- large objects than the standard. Internally, the driver uses the
- extension to provide large object support.
- </para>
+ <note><para>In a future release of the
+ <acronym>JDBC</acronym> Driver, the <function>getBLOB()</function>
+ and <function>setBLOB()</function> methods may no longer
+ interact with Large Objects and will instead work on
+ <type>bytea</type> datatypes. So it is recommended that you
+ use the <classname>LargeObject</classname> <acronyn>API</acronym>
+ if you intend to use Large Objects.
+ </para></note>
- <para>
- In <acronym>JDBC</acronym>, the standard way to access Large
- Objects is using the <function>getBinaryStream()</function> method
- in <classname>ResultSet</classname>, and
- <function>setBinaryStream()</function> method in
- <classname>PreparedStatement</classname>. These methods make the
- large object appear as a Java stream, allowing you to use the
- <literal>java.io</literal> package, and others, to manipulate the
- object. <xref linkend="jdbc-lo-example"> illustrates the usage of
- this approach.
- </para>
- <example id="jdbc-lo-example">
- <title>Using the <acronym>JDBC</acronym> Large Object Interface</title>
+ <example id="jdbc-binary-data-example">
+ <title>Binary Data Examples</title>
<para>
For example, suppose you have a table containing the file name of
- an image and you have a large object containing that image:
+ an image and you also want to store the image in a <type>bytea</type>
+ column:
<programlisting>
-CREATE TABLE images (imgname text, imgoid oid);
+CREATE TABLE images (imgname text, img bytea);
</programlisting>
</para>
<programlisting>
File file = new File("myimage.gif");
FileInputStream fis = new FileInputStream(file);
-PreparedStatement ps = conn.prepareStatement("INSERT INTO images VALUES (?, ?)"); <co id="co.jdbc-qmark">
+PreparedStatement ps = conn.prepareStatement("INSERT INTO images VALUES (?, ?)");
ps.setString(1, file.getName());
ps.setBinaryStream(2, fis, file.length());
ps.executeUpdate();
ps.close();
fis.close();
</programlisting>
- <calloutlist>
- <callout arearefs="co.jdbc-qmark">
- <para>
- The question marks must appear literally. The actual data is
- substituted by the next lines.
- </para>
- </callout>
- </calloutlist>
- Here, <function>setBinaryStream</function> transfers a set number
- of bytes from a stream into a Large Object, and stores the OID
- into the field holding a reference to it. Notice that the
- creation of the Large Object itself in the database happens
- transparently.
+
+ Here, <function>setBinaryStream()</function> transfers a set number
+ of bytes from a stream into the column of type <type>bytea</type>.
+ This also could have been done using the <function>setBytes()</function>
+ method if the contents of the image was already in a
+ <classname>byte[]</classname>.
</para>
<para>
<classname>Statement</classname> class can equally be used.)
<programlisting>
-PreparedStatement ps = con.prepareStatement("SELECT imgoid FROM images WHERE imgname=?");
+PreparedStatement ps = con.prepareStatement("SELECT img FROM images WHERE imgname=?");
ps.setString(1, "myimage.gif");
ResultSet rs = ps.executeQuery();
if (rs != null) {
while(rs.next()) {
- InputStream is = rs.getBinaryStream(1);
+ byte[] imgBytes = rs.getBytes(1);
// use the stream in some way here
- is.close();
}
rs.close();
}
<para>
Here you can see how the Large Object is retrieved as an
- <classname>InputStream</classname>. You will also notice that we
- close the stream before processing the next row in the
- result. This is part of the <acronym>JDBC</acronym> specification,
- which states that any <classname>InputStream</classname> returned
- is closed when <function>ResultSet.next()</function> or
- <function>ResultSet.close()</function> is called.
+ <classname>byte[]</classname>. You could have used a
+ <classname>InputStream</classname> object instead.
</para>
+
+ <para>
+ Alternativly you could be storing a very large file and want to use
+ the <classname>LargeObject</classname> <acronym>API</acronym> to
+ store the file:
+<programlisting>
+CREATE TABLE imagesLO (imgname text, imgOID OID);
+</programlisting>
+ </para>
+
+ <para>
+ To insert an image, you would use:
+<programlisting>
+// All LargeObject API calls must be within a transaction
+conn.setAutoCommit(false);
+LargeObjectManager lobj = ((org.postgresql.Connection)conn).getLargeObjectAPI();
+
+//create a new large object
+int oid = lobj.create(LargeObjectManager.READ | LargeObjectManager.WRITE);
+
+//open the large object for write
+LargeObject obj = lobj.open(oid, LargeObjectManager.WRITE);
+
+// Now open the file
+File file = new File("myimage.gif");
+FileInputStream fis = new FileInputStream(file);
+
+// copy the data from the file to the large object
+byte buf[] = new byte[2048];
+int s, tl = 0;
+while ((s = fis.read(buf, 0, 2048)) > 0)
+{
+ obj.write(buf, 0, s);
+ tl += s;
+}
+
+// Close the large object
+obj.close();
+
+//Now insert the row into imagesLO
+PreparedStatement ps = conn.prepareStatement("INSERT INTO imagesLO VALUES (?, ?)");
+ps.setString(1, file.getName());
+ps.setInt(2, oid);
+ps.executeUpdate();
+ps.close();
+fis.close();
+</programlisting>
+
+ <para>
+ Retrieving the image from the Large Object:
+
+<programlisting>
+// All LargeObject API calls must be within a transaction
+conn.setAutoCommit(false);
+LargeObjectManager lobj = ((org.postgresql.Connection)conn).getLargeObjectAPI();
+
+PreparedStatement ps = con.prepareStatement("SELECT imgOID FROM imagesLO WHERE imgname=?");
+ps.setString(1, "myimage.gif");
+ResultSet rs = ps.executeQuery();
+if (rs != null) {
+ while(rs.next()) {
+ //open the large object for reading
+ int oid = rs.getInt(1);
+ LargeObject obj = lobj.open(oid, LargeObjectManager.READ);
+
+ //read the data
+ byte buf[] = new byte[obj.size()];
+ obj.read(buf, 0, obj.size());
+ //do something with the data read here
+ }
+ // Close the object
+ obj.close();
+ }
+ rs.close();
+}
+ps.close();
+</programlisting>
+ </para>
+
</example>
</sect1>
</para>
<para>
- Normally, client code would use the getAsciiStream,
- getBinaryStream, or getUnicodeStream methods in <classname>ResultSet</classname>, or
- setAsciiStream, setBinaryStream, or setUnicodeStream methods in
- <classname>PreparedStatement</classname> to access Large Objects.
+ Normally, client code would use the methods in
+ <classname>BLOB</classname> to access large objects.
</para>
<para>
- However, sometimes lower level access to Large Objects are
- required, that
are not supported by the <acronym>JDBC</acronym>
+ However, sometimes lower level access to Large Objects is
+ required, that
is not supported by the <acronym>JDBC</acronym>
specification.
</para>
</para>
<para>
- 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
+ Normally, client code would use the <classname>BLOB</classname>
+ methods to access large objects. However, sometimes
+ lower level access to Large Objects is required, that is not
supported by the <acronym>JDBC</acronym> specification.
</para>
</sect3>
</sect2>
-
- <sect2>
- <title>Object Serialization</title>
-
- <para>
- <productname>PostgreSQL</productname> is not a normal
- <acronym>SQL</acronym> database. It is more extensible than most
- other databases, and does support object oriented features that
- are unique to it.
- </para>
-
- <para>
- One of the consequences of this, is that you can have one table
- refer to a row in another table. For example:
-<screen>
-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)
-</screen>
- Okay, 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.
- </para>
-
- <para>
- What does this have to do with Java?
- </para>
-
- <para>
- 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.
- </para>
-
- <para>
- Now, under <acronym>JDBC</acronym>, you would have to use a
- Large Object to store them. However, you cannot perform queries on
- those objects.
- </para>
-
- <para>
- What the org.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.
- </para>
-
- <para>
- Sound's complicated? In fact, it's simpler than what I wrote -
- it's just difficult to explain.
- </para>
-
- <para>
- 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
- <command>CREATE TABLE</command> statements to the database, based on a Java Object
- or Class that you want to serialize.
- </para>
-
- <para>
- Oh, one last thing. If your object contains a line like:
-<programlisting>
-public int oid;
-</programlisting>
- 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.
- </para>
-
- <para>
- 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.
- </para>
-
- <para>
- Setting oid to 0 before serialization, will also cause the object
- to be inserted. This enables an object to be duplicated in the
- database.
- </para>
-
-<programlisting>
-Class org.postgresql.util.Serialize
-
-java.lang.Object
- |
- +----org.postgresql.util.Serialize
-
- public class Serialize extends Object
-
- This class uses <productname>PostgreSQL</productname>'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(org.postgresql.Connection c,
- String type) throws SQLException
-
- This creates an instance that can be used to serialize
-or deserialize a Java object from a <productname>PostgreSQL</productname> 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(org.postgresql.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(org.postgresql.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 <productname>PostgreSQL</productname> 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 <productname>PostgreSQL</productname>).
-
- Parameters:
- name - Class name
-
- Returns:
- <productname>PostgreSQL</productname> table name
-
- Throws: SQLException
- on error
-
- public static String toClassName(String name) throws SQLException
-
- This converts a <productname>PostgreSQL</productname> table to a Java Class name, by
- replacing _ with .
-
- Parameters:
- name - <productname>PostgreSQL</productname> table name
-
- Returns:
- Class name
-
- Throws: SQLException
- on error
-<!-- **************************************************************** -->
-Utility Classes
-
-The org.postgresql.util package contains classes used by the internals of
-the main driver, and the other extensions.
-
-Class org.postgresql.util.PGmoney
-
-java.lang.Object
- |
- +----org.postgresql.util.PGobject
- |
- +----org.postgresql.util.PGmoney
-
- public class PGmoney extends PGobject implements Serializable,
-Cloneable
-
- This implements a class that handles the <productname>PostgreSQL</productname> 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
-
- Create a money.
-
- Parameters:
- value - Definition of this money in <productname>PostgreSQL</productname>'s
-syntax
-
- public PGmoney()
-
- Required by the driver
-
-Methods
-
- public void setValue(String s) throws SQLException
-
- Parameters:
- s - Definition of this money in <productname>PostgreSQL</productname>'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 moneys 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 PGmoney in the syntax expected by <productname>PostgreSQL</productname>
-
- Overrides:
- getValue in class PGobject
-
-<!-- **************************************************************** -->
-Class org.postgresql.util.PGobject
-
-java.lang.Object
- |
- +----org.postgresql.util.PGobject
-
- public class PGobject extends Object implements Serializable,
-Cloneable
-
- This class is used to describe data types that are unknown by
- <acronym>JDBC</acronym>
-Standard.
- A call to org.postgresql.Connection permits a class that extends this
-class to be associated with a named type. This is how the
-org.postgresql.geometric package operates.
- ResultSet.getObject() will return this class for any type that is
-not recognized on having it's own handler. Because of this, any
-<productname>PostgreSQL</productname> data type is supported.
-
-Constructors
-
- public PGobject()
-
- This is called by org.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
-overridden.
-
- 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 overridden, to return the value of the object,
-in the form required by <productname>PostgreSQL</productname>.
-
- Returns:
- the value of this object
-
- public boolean equals(Object obj)
-
- This must be overridden to allow comparisons of objects
-
- Parameters:
- obj - Object to compare with
-
- Returns:
- true if the two objects are identical
-
- Overrides:
- equals in class Object
-
- public Object clone()
-
- This must be overridden to allow the object to be cloned
-
- Overrides:
- clone in class Object
-
- public String toString()
-
- This is defined here, so user code need not override it.
-
- Returns:
- the value of this object, in the syntax expected by
-<productname>PostgreSQL</productname>
-
- Overrides:
- toString in class Object
-
-<!-- **************************************************************** -->
-Class org.postgresql.util.PGtokenizer
-
-java.lang.Object
- |
- +----org.postgresql.util.PGtokenizer
-
- public class PGtokenizer extends Object
-
- This class is used to tokenize the text output of <productname>PostgreSQL</productname>.
-
- 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 <productname>PostgreSQL</productname>.
-
- See Also:
- PGbox, PGcircle, PGlseg, PGpath, PGpoint, PGpolygon
-
-Constructors
-
- public PGtokenizer(String string,
- char delim)
-
- Create a tokenizer.
-
- 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 data types 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
-
- 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
-
- 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
-
-<!-- **************************************************************** -->
-Class org.postgresql.util.Serialize
-
-This was documented earlier under Object Serialization.
-
-Class org.postgresql.util.UnixCrypt
-
-java.lang.Object
- |
- +----org.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.
-
- (Invalid URL) http://www.zeh.com/local/jfd/crypt.html
-
-Methods
-
- public static final String crypt(String salt,
- String original)
-
- Encrypt a password given the clear-text password and a
-<quote>salt</quote>.
-
- 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 randomized.
- 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 clear-text 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 acquired).
-
- Returns:
- true if the password should be considered correct.
-</programlisting>
- </sect2>
-
</sect1>
-<!-- **************************************************************** -->
+
<sect1 id="jdbc-thread">
<title>Using the driver in a multi-threaded or a servlet environment</title>
</para>
<para>
- <productname>PostgreSQL</productname> 6.4 brought thread safety to
- the entire driver. (Standard <acronym>JDBC</acronym> was thread
- safe in 6.3, but the Fastpath <acronym>API</acronym> was not.)
+ The <productname>PostgreSQL</productname> <acronyn>JDBC</acronym> Driver
+ is thread safe.
Consequently, if your application uses multiple threads then you do
not have to worry about complex algorithms to ensure that only one
uses the database at any time.
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