largeobjectmanager.java

关系型数据库 Postgresql 6.5.2

package postgresql.largeobject;

import java.io.*;
import java.lang.*;
import java.net.*;
import java.util.*;
import java.sql.*;

import postgresql.fastpath.*;
import postgresql.util.*;

/**
 * This class implements the large object interface to postgresql.
 *
 * <p>It provides methods that allow client code to create, open and delete
 * large objects from the database. When opening an object, an instance of
 * postgresql.largeobject.LargeObject is returned, and its methods then allow
 * access to the object.
 *
 * <p>This class can only be created by postgresql.Connection
 *
 * <p>To get access to this class, use the following segment of code:
 * <br><pre>
 * import postgresql.largeobject.*;
 *
 * Connection  conn;
 * LargeObjectManager lobj;
 *
 * ... code that opens a connection ...
 *
 * lobj = ((postgresql.Connection)myconn).getLargeObjectAPI();
 * </pre>
 *
 * <p>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.
 *
 * <p>However, sometimes lower level access to Large Objects are required,
 * that are not supported by the JDBC specification.
 *
 * <p>Refer to postgresql.largeobject.LargeObject on how to manipulate the
 * contents of a Large Object.
 *
 * @see postgresql.largeobject.LargeObject
 * @see postgresql.ResultSet#getAsciiStream
 * @see postgresql.ResultSet#getBinaryStream
 * @see postgresql.ResultSet#getUnicodeStream
 * @see postgresql.PreparedStatement#setAsciiStream
 * @see postgresql.PreparedStatement#setBinaryStream
 * @see postgresql.PreparedStatement#setUnicodeStream
 * @see java.sql.ResultSet#getAsciiStream
 * @see java.sql.ResultSet#getBinaryStream
 * @see java.sql.ResultSet#getUnicodeStream
 * @see java.sql.PreparedStatement#setAsciiStream
 * @see java.sql.PreparedStatement#setBinaryStream
 * @see java.sql.PreparedStatement#setUnicodeStream
 */
public class LargeObjectManager
{
  // the fastpath api for this connection
  private Fastpath fp;
  
  /**
   * This mode indicates we want to write to an object
   */
  public static final int WRITE   = 0x00020000;
  
  /**
   * This mode indicates we want to read an object
   */
  public static final int READ    = 0x00040000;
  
  /**
   * This mode is the default. It indicates we want read and write access to
   * a large object
   */
  public static final int READWRITE = READ | WRITE;
  
  /**
   * This prevents us being created by mere mortals
   */
  private LargeObjectManager()
  {
  }
  
  /**
   * Constructs the LargeObject API.
   *
   * <p><b>Important Notice</b>
   * <br>This method should only be called by postgresql.Connection
   *
   * <p>There should only be one LargeObjectManager per Connection. The
   * postgresql.Connection class keeps track of the various extension API's
   * and it's advised you use those to gain access, and not going direct.
   */
  public LargeObjectManager(postgresql.Connection conn) throws SQLException
  {
    // We need Fastpath to do anything
    this.fp = conn.getFastpathAPI();
    
    // Now get the function oid's for the api
    //
    // This is an example of Fastpath.addFunctions();
    //
    java.sql.ResultSet res = (java.sql.ResultSet)conn.createStatement().executeQuery("select proname, oid from pg_proc" +
				      " where proname = 'lo_open'" +
				      "    or proname = 'lo_close'" +
				      "    or proname = 'lo_creat'" +
				      "    or proname = 'lo_unlink'" +
				      "    or proname = 'lo_lseek'" +
				      "    or proname = 'lo_tell'" +
				      "    or proname = 'loread'" +
				      "    or proname = 'lowrite'");
    
    if(res==null)
      throw new PSQLException("postgresql.lo.init");
    
    fp.addFunctions(res);
    res.close();
    DriverManager.println("Large Object initialised");
  }
  
  /**
   * This opens an existing large object, based on its OID. This method
   * assumes that READ and WRITE access is required (the default).
   *
   * @param oid of large object
   * @return LargeObject instance providing access to the object
   * @exception SQLException on error
   */
  public LargeObject open(int oid) throws SQLException
  {
    return new LargeObject(fp,oid,READWRITE);
  }
  
  /**
   * This opens an existing large object, based on its OID
   *
   * @param oid of large object
   * @param mode mode of open
   * @return LargeObject instance providing access to the object
   * @exception SQLException on error
   */
  public LargeObject open(int oid,int mode) throws SQLException
  {
    return new LargeObject(fp,oid,mode);
  }
  
  /**
   * This creates a large object, returning its OID.
   *
   * <p>It defaults to READWRITE for the new object's attributes.
   *
   * @return oid of new object
   * @exception SQLException on error
   */
  public int create() throws SQLException
  {
    FastpathArg args[] = new FastpathArg[1];
    args[0] = new FastpathArg(READWRITE);
    return fp.getInteger("lo_creat",args);
  }
  
  /**
   * This creates a large object, returning its OID
   *
   * @param mode a bitmask describing different attributes of the new object
   * @return oid of new object
   * @exception SQLException on error
   */
  public int create(int mode) throws SQLException
  {
    FastpathArg args[] = new FastpathArg[1];
    args[0] = new FastpathArg(mode);
    return fp.getInteger("lo_creat",args);
  }
  
  /**
   * This deletes a large object.
   *
   * @param oid describing object to delete
   * @exception SQLException on error
   */
  public void delete(int oid) throws SQLException
  {
    FastpathArg args[] = new FastpathArg[1];
    args[0] = new FastpathArg(oid);
    fp.fastpath("lo_unlink",false,args);
  }
  
  /**
   * This deletes a large object.
   *
   * <p>It is identical to the delete method, and is supplied as the C API uses
   * unlink.
   *
   * @param oid describing object to delete
   * @exception SQLException on error
   */
  public void unlink(int oid) throws SQLException
  {
    delete(oid);
  }
  
}