statement.java

SSD9 练习9

/*
 * MM JDBC Drivers for MySQL
 *
 * $Id: Statement.java,v 1.2 1998/08/25 00:53:48 mmatthew Exp $
 *
 * Copyright (C) 1998 Mark Matthews <[e-mail]>
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA  02111-1307, USA.
 *
 * See the COPYING file located in the top-level-directory of
 * the archive of this library for complete text of license.
 *
 * Some portions:
 *
 * Copyright (c) 1996 Bradley McLean / Jeffrey Medeiros
 * Modifications Copyright (c) 1996/1997 Martin Rode
 * Copyright (c) 1997 Peter T Mount
 */

/**
 * A Statement object is used for executing a static SQL statement and
 * obtaining the results produced by it.
 *
 * <p>Only one ResultSet per Statement can be open at any point in time.
 * Therefore, if the reading of one ResultSet is interleaved with the
 * reading of another, each must have been generated by different
 * Statements.  All statement execute methods implicitly close a
 * statement's current ResultSet if an open one exists.
 *
 * @see java.sql.Statement
 * @see ResultSet
 * @author Mark Matthews <[e-mail]>
 * @version $Id$
 */

package org.gjt.mm.mysql;

import java.sql.*;

public class Statement implements java.sql.Statement
{
    Connection      _Conn             = null; // The connection who created us
    ResultSet       _Results          = null; // The current results
    ResultSet       _NextResults      = null; // The next result set
    SQLWarning      _Warnings         = null; // The warnings chain.
    int             _timeout          = 0;    // The timeout for a query
    boolean         _escapeProcessing = true; // escape processing flag
    EscapeProcessor _Escaper          = null; // The escape processor

    int             _max_field_size   = MysqlIO.MAXBUF;
    int             _max_rows         = -1;

    long            _update_count            = -1;
    long            _last_insert_id          = -1;

    String          _Catalog = null;

    /**
     * Constructor for a Statement.  It simply sets the connection
     * that created us.
     *
     * @param c the Connection instantation that creates us
     */

    public Statement(Connection C, String Catalog)
    {
	if (Driver.trace) {
	    Object[] Args = {C};
	    Debug.methodCall(this, "constructor", Args);
	}

	_Conn = C;
	_Escaper = new EscapeProcessor();
	_Catalog = Catalog;
    }

    /**
     * Execute a SQL statement that retruns a single ResultSet
     *
     * @param Sql typically a static SQL SELECT statement
     * @return a ResulSet that contains the data produced by the query
     * @exception java.sql.SQLException if a database access error occurs
     */

    public java.sql.ResultSet executeQuery(String Sql) throws java.sql.SQLException
    {
	if (Driver.trace) {
	    Object[] Args = {Sql};
	    Debug.methodCall(this, "executeQuery", Args);
	}
      
	if (_escapeProcessing) {
	    Sql = _Escaper.escapeSQL(Sql);
	}

	if (Sql.indexOf("||") != -1) {
	    Sql = _Escaper.doConcat(Sql);
	}
       
	if (_Results != null) {
	    _Results.close();
	}

	// If there isn't a limit clause in the SQL
	// then limit the number of rows to return in 
	// an efficient manner. Only do this if
	// setMaxRows() hasn't been used on any Statements
	// generated from the current Connection (saves
	// a query, and network traffic).

      synchronized (_Conn.getMutex()) {
          String OldCatalog = null;

          if (!_Conn.getCatalog().equals(_Catalog)) {
           OldCatalog = _Conn.getCatalog();
           _Conn.setCatalog(_Catalog);
          }

          if (_Conn.useMaxRows()) {

	      // We need to execute this all together
	      // So synchronize on the Connection's mutex (because 
	      // even queries going through there synchronize
	      // on the connection

  	      if (Sql.toUpperCase().indexOf("LIMIT") != -1) { 
	        _Results = _Conn.execSQL(Sql, _max_rows);
	      }
	      else {
		    if (_max_rows <= 0) {
			_Conn.execSQL("SET OPTION SQL_SELECT_LIMIT=" 
				      + MysqlDefs.MAX_ROWS, -1);
		    }
		    else {
			_Conn.execSQL("SET OPTION SQL_SELECT_LIMIT=" + _max_rows,-1);
		    }
                		            
		    _Results = _Conn.execSQL(Sql, -1);

                if (OldCatalog != null) {
                  _Conn.setCatalog(OldCatalog);
                }
		}
	  }
	  else {
	    _Results = _Conn.execSQL(Sql, -1);	    
	  }

        if (OldCatalog != null) {
          _Conn.setCatalog(OldCatalog);
        }
      }

	_last_insert_id = _Results.getUpdateID();
	_NextResults = _Results;
	_Results.setConnection(_Conn);
	return _Results;
    }

    /**
     * Execute a SQL INSERT, UPDATE or DELETE statement.  In addition
     * SQL statements that return nothing such as SQL DDL statements
     * can be executed
     *
     * Any IDs generated for AUTO_INCREMENT fields can be retrieved
     * by casting this Statement to org.gjt.mm.mysql.Statement and
     * calling the getLastInsertID() method.
     *
     * @param Sql a SQL statement
     * @return either a row count, or 0 for SQL commands
     * @exception java.sql.SQLException if a database access error occurs
     */

    public int executeUpdate(String Sql) throws java.sql.SQLException
    {
	if (Driver.trace) {
	    Object[] Args = {Sql};
	    Debug.methodCall(this, "executeUpdate", Args);
	}
	
	if (_escapeProcessing) {
	    Sql = _Escaper.escapeSQL(Sql);
	}

	if (Sql.indexOf("||") != -1) {
	    Sql = _Escaper.doConcat(Sql);
	}

      // The checking and changing of catalogs
      // must happen in sequence, so synchronize
      // on the same mutex that _Conn is using

	ResultSet RS = null;

	synchronized (_Conn.getMutex()) {
        String OldCatalog = null;

        if (!_Conn.getCatalog().equals(_Catalog)) {
          OldCatalog = _Conn.getCatalog();
          _Conn.setCatalog(_Catalog);
        }

	  RS = _Conn.execSQL(Sql, -1);
   
          RS.setConnection(_Conn);

	  if (OldCatalog != null) {
          _Conn.setCatalog(OldCatalog);
        }
      }
	
	if (RS.reallyResult()) {
	    throw new java.sql.SQLException("Results returned for UPDATE ONLY.", "01S03");
	}
	else {
	    _update_count = RS.getUpdateCount();
	    
	    int truncated_update_count = 0;

	    if (_update_count > Integer.MAX_VALUE) {
		truncated_update_count = Integer.MAX_VALUE;
	    }
	    else {
		truncated_update_count = (int)_update_count;
	    }

	    _last_insert_id = RS.getUpdateID();
	    
	    return truncated_update_count;
	}
    }

    /**
     * In many cases, it is desirable to immediately release a
     * Statement's database and JDBC resources instead of waiting
     * for this to happen when it is automatically closed.  The
     * close method provides this immediate release.
     *
     * <p><B>Note:</B> A Statement is automatically closed when it is
     * garbage collected.  When a Statement is closed, its current
     * ResultSet, if one exists, is also closed.
     *
     * @exception java.sql.SQLException if a database access error occurs
     */

    public void close() throws java.sql.SQLException
    {
	if (Driver.trace) {
	    Object[] Args = new Object[0];
	    Debug.methodCall(this, "close", Args);
	}

	_Results  = null;
	_Conn     = null;
	_Warnings = null;
	_Escaper  = null;
    }
  
    /**
     * The maxFieldSize limit (in bytes) is the maximum amount of
     * data returned for any column value; it only applies to
     * BINARY, VARBINARY, LONGVARBINARY, CHAR, VARCHAR and LONGVARCHAR
     * columns.  If the limit is exceeded, the excess data is silently
     * discarded.
     *
     * @return the current max column size limit; zero means unlimited
     * @exception java.sql.SQLException if a database access error occurs
     */

    public int getMaxFieldSize() throws java.sql.SQLException
    {
	if (Driver.trace) {
	    Object[] Args = new Object[0];
	    Debug.methodCall(this, "getMaxFieldSize", Args);
	}

	return _max_field_size; // Init. set to MAXBUFFER in MysqlIO
    }

    /**
     * Sets the maxFieldSize
     *
     * @param max the new max column size limit; zero means unlimited
     * @exception java.sql.SQLException if size exceeds buffer size
     */

    public void setMaxFieldSize(int max) throws java.sql.SQLException
    {
	if (Driver.trace) {
	    Object[] Args = {new Integer(max)};
	    Debug.methodCall(this, "setMaxFieldSize", Args);
	}

	if (max > MysqlIO.MAXBUF)
	    throw new java.sql.SQLException("Attempt to set max field size > " + MysqlIO.MAXBUF + " (compile time default)", "S1009");
	else
	    _max_field_size = max;
    }

    /**
     * The maxRows limit is set to limit the number of rows that
     * any ResultSet can contain.  If the limit is exceeded, the
     * excess rows are silently dropped.
     *
     * @return the current maximum row limit; zero means unlimited
     * @exception java.sql.SQLException if a database access error occurs
     */

    public int getMaxRows() throws java.sql.SQLException
    {
	if (Driver.trace) {
	    Object[] Args = new Object[0];
	    Debug.methodCall(this, "getMaxRows", Args);
	}

	if (_max_rows <=0) {
	    return 0;
	}
	else {
	    return _max_rows;
	}
    }

    /**
     * Set the maximum number of rows
     *
     * @param max the new max rows limit; zero means unlimited
     * @exception java.sql.SQLException if a database access error occurs
     * @see getMaxRows
     */

    public void setMaxRows(int max) throws java.sql.SQLException
    {
	if (Driver.trace) {
	    Object[] Args = {new Integer(max)};
	    Debug.methodCall(this, "setMaxRows", Args);
	}

	if (max > MysqlDefs.MAX_ROWS) {
	    throw new java.sql.SQLException("setMaxRows() out of range. " + max + " > " + MysqlDefs.MAX_ROWS + ".", "S1009");
	}

	if (max == 0) {
	    max = -1;
	}

	_max_rows = max;

	// Most people don't use setMaxRows()
	// so don't penalize them
	// with the extra query it takes
	// to do it efficiently unless we need
	// to.