largeobject.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.*;

/**
 * This class implements the large object interface to postgresql.
 *
 * <p>It provides the basic methods required to run the interface, plus
 * a pair of methods that provide InputStream and OutputStream classes
 * for this object.
 *
 * <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.LargeObjectManager on how to gain access
 * to a Large Object, or how to create one.
 *
 * @see postgresql.largeobject.LargeObjectManager
 * @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 LargeObject
{
  /**
   * Indicates a seek from the begining of a file
   */
  public static final int SEEK_SET = 0;
  
  /**
   * Indicates a seek from the current position
   */
  public static final int SEEK_CUR = 1;
  
  /**
   * Indicates a seek from the end of a file
   */
  public static final int SEEK_END = 2;
  
  private Fastpath	fp;	// Fastpath API to use
  private int		oid;	// OID of this object
  private int		fd;	// the descriptor of the open large object
  
  /**
   * This opens a large object.
   *
   * <p>If the object does not exist, then an SQLException is thrown.
   *
   * @param fp FastPath API for the connection to use
   * @param oid of the Large Object to open
   * @param mode Mode of opening the large object
   * (defined in LargeObjectManager)
   * @exception SQLException if a database-access error occurs.
   * @see postgresql.largeobject.LargeObjectManager
   */
  protected LargeObject(Fastpath fp,int oid,int mode) throws SQLException
  {
    this.fp = fp;
    this.oid = oid;
    
    FastpathArg args[] = new FastpathArg[2];
    args[0] = new FastpathArg(oid);
    args[1] = new FastpathArg(mode);
    this.fd = fp.getInteger("lo_open",args);
  }
  
  /**
   * @return the OID of this LargeObject
   */
  public int getOID()
  {
    return oid;
  }
  
  /**
   * This method closes the object. You must not call methods in this
   * object after this is called.
   * @exception SQLException if a database-access error occurs.
   */
  public void close() throws SQLException
  {
    FastpathArg args[] = new FastpathArg[1];
    args[0] = new FastpathArg(fd);
    fp.fastpath("lo_close",false,args); // true here as we dont care!!
  }
  
  /**
   * Reads some data from the object, and return as a byte[] array
   *
   * @param len number of bytes to read
   * @return byte[] array containing data read
   * @exception SQLException if a database-access error occurs.
   */
    public byte[] read(int len) throws SQLException
    {
	// This is the original method, where the entire block (len bytes)
	// is retrieved in one go.
	FastpathArg args[] = new FastpathArg[2];
	args[0] = new FastpathArg(fd);
	args[1] = new FastpathArg(len);
	return fp.getData("loread",args);
	
	// This version allows us to break this down into 4k blocks
	//if(len<=4048) {
	//// handle as before, return the whole block in one go
	//FastpathArg args[] = new FastpathArg[2];
	//args[0] = new FastpathArg(fd);
	//args[1] = new FastpathArg(len);
	//return fp.getData("loread",args);
	//} else {
	//// return in 4k blocks
	//byte[] buf=new byte[len];
	//int off=0;
	//while(len>0) {
	//int bs=4048;
	//len-=bs;
	//if(len<0) {
	//bs+=len;
	//len=0;
	//}
	//read(buf,off,bs);
	//off+=bs;
	//}
	//return buf;
	//}
    }
    
  /**
   * Reads some data from the object into an existing array
   *
   * @param buf destination array
   * @param off offset within array
   * @param len number of bytes to read
   * @exception SQLException if a database-access error occurs.
   */
  public void read(byte buf[],int off,int len) throws SQLException
  {
    System.arraycopy(read(len),0,buf,off,len);
  }
  
  /**
   * Writes an array to the object
   *
   * @param buf array to write
   * @exception SQLException if a database-access error occurs.
   */
  public void write(byte buf[]) throws SQLException
  {
    FastpathArg args[] = new FastpathArg[2];
    args[0] = new FastpathArg(fd);
    args[1] = new FastpathArg(buf);
    fp.fastpath("lowrite",false,args);
  }
  
  /**
   * Writes some data from an array to the object
   *
   * @param buf destination array
   * @param off offset within array
   * @param len number of bytes to write
   * @exception SQLException if a database-access error occurs.
   */
  public void write(byte buf[],int off,int len) throws SQLException
  {
    byte data[] = new byte[len];
    System.arraycopy(buf,off,data,0,len);
    write(data);
  }
  
  /**
   * Sets the current position within the object.
   *
   * <p>This is similar to the fseek() call in the standard C library. It
   * allows you to have random access to the large object.
   *
   * @param pos position within object
   * @param ref Either SEEK_SET, SEEK_CUR or SEEK_END
   * @exception SQLException if a database-access error occurs.
   */
  public void seek(int pos,int ref) throws SQLException
  {
    FastpathArg args[] = new FastpathArg[3];
    args[0] = new FastpathArg(fd);
    args[1] = new FastpathArg(pos);
    args[2] = new FastpathArg(ref);
    fp.fastpath("lo_lseek",false,args);
  }
  
  /**
   * Sets the current position within the object.
   *
   * <p>This is similar to the fseek() call in the standard C library. It
   * allows you to have random access to the large object.
   *
   * @param pos position within object from begining
   * @exception SQLException if a database-access error occurs.
   */
  public void seek(int pos) throws SQLException
  {
    seek(pos,SEEK_SET);
  }
  
  /**
   * @return the current position within the object
   * @exception SQLException if a database-access error occurs.
   */
  public int tell() throws SQLException
  {
    FastpathArg args[] = new FastpathArg[1];
    args[0] = new FastpathArg(fd);
    return fp.getInteger("lo_tell",args);
  }
  
  /**
   * This method is inefficient, as the only way to find out the size of
   * the object is to seek to the end, record the current position, then
   * return to the original position.
   *
   * <p>A better method will be found in the future.
   *
   * @return the size of the large object
   * @exception SQLException if a database-access error occurs.
   */
  public int size() throws SQLException
  {
    int cp = tell();
    seek(0,SEEK_END);
    int sz = tell();
    seek(cp,SEEK_SET);
    return sz;
  }
  
  /**
   * Returns an InputStream from this object.
   *
   * <p>This InputStream can then be used in any method that requires an
   * InputStream.
   *
   * @exception SQLException if a database-access error occurs.
   */
  public InputStream getInputStream() throws SQLException
  {
    throw postgresql.Driver.notImplemented();
  }
  
  /**
   * Returns an OutputStream to this object
   *
   * <p>This OutputStream can then be used in any method that requires an
   * OutputStream.
   *
   * @exception SQLException if a database-access error occurs.
   */
  public OutputStream getOutputStream() throws SQLException
  {
    throw postgresql.Driver.notImplemented();
  }
}