dbaccess.java

一个OR Mapping 工具

package org.dbgen.support;

import java.util.*;
import java.sql.*;

/**
 * DbAccess is a thin layer API sitting on top of JDBC
 * Connection/Statement, and is used conveniently to access data
 * sources by dynamically creating JDBC Statement's as necessary from
 * a single connection.  When a ResultSet is closed, the Statement
 * will be re-used in the next query/update operation.
 *
 * <p>Example:
 *
 * <pre>
 * String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
 * String url    = "jdbc:odbc:datasrc";
 * DbAccess dba  = new DbAccess(drv, url, "USER", "PASS");
 * ResultSet rs  = dba.executeQuery("select * from tablename");
 * while (rs.next()) {
 *    // do something with the result set.
 * }
 * dba.close(rs); // free the Statement for this ResultSet
 * </pre>
 */
public class DbAccess
{

  protected Connection conn = null;
  protected String driver = null;
  protected String url = null;
  protected String user = null;
  protected String password = null;
  private Vector srs = new Vector(2);

  boolean fieldDebug = false;

  Handler fieldErrorHandler = null;
  protected transient java.beans.PropertyChangeSupport propertyChange = new java.beans.PropertyChangeSupport(this);

  /**
   * Construct a DbAccess object.  The programmer must set the driver,
   * url, username, and password properties, and call
   * <code>connect()</code> before using other methods in this class.
   */
  public DbAccess()
  {
  }

  /**
   * Construct a DbAccess with the specified JDBC Driver class,
   * JDBC url, username and password.
   * @exception java.sql.SQLException If database connection failed.
   * @exception ClassNotFoundException If the specified driver is not found.
   */
  public DbAccess(String driver, String url, String user, String password)
    throws SQLException, ClassNotFoundException
  {
    this.driver = driver;
    this.url = url;
    this.user = user;
    this.password = password;
    connect(true);
  }

  /**
   * Construct a DbAccess object with the specified JDBC Connection.
   */
  public DbAccess(Connection conn)
  {
    this.conn = conn;
  }

  /**
   * The addPropertyChangeListener method was generated to support the propertyChange field.
   */
  public synchronized void addPropertyChangeListener(java.beans.PropertyChangeListener listener) {
    propertyChange.addPropertyChangeListener(listener);
  }

  /**
   * Close the specified ResultSet.  This function MUST BE CALLED so
   * that the JDBC Statement can be re-used in subsequent database
   * operations.  Failure to do so may exhaust system resources.
   * @exception java.sql.SQLException If
   * <code>java.sql.ResultSet.close()</code> failed.
   */
  public void close(ResultSet rs)
    throws SQLException
  {
    for (int i = 0; i < srs.size(); i++) {
      SRPair obj = (SRPair) srs.elementAt(i);

      if (obj.resultset == rs) {
        obj.inuse = false;

        //	Util.println("* Free SRPair " + obj);
      }
    }

    rs.close();
  }

  /**
   * Connect to database now.
   * @exception java.sql.SQLException If database connection failed.
   * @exception ClassNotFoundException If the specified driver is not found.
   */
  public void connect(boolean reconnect)
    throws SQLException, ClassNotFoundException
  {
    Class.forName(driver);

    if (reconnect && conn != null)
    {
      conn.close();
      conn = null;
    }

    if (conn == null) {
      if (user == null || password == null) {
        conn = DriverManager.getConnection(url);
      } else {
        conn = DriverManager.getConnection(url, user, password);
      }

      //System.out.println("Data Source: " + url + " connected as " + conn);
    }
  }

  /**
   * Disconnect from the current JDBC connection.
   * @exception java.sql.SQLException When a SQL Exception occurred.
   */
  public void disconnect()
    throws SQLException
  {
    if (conn != null)
    {
      conn.close();
      conn = null;
    }

    return;
  }

  /**
   * Execute a SQL statement.  return The ResultSet for this query.
   * @exception java.sql.SQLException If <code>java.sql.Statement.executeQuery()</code> failed.
   * @return A <code>java.sql.ResultSet</code> object.
   */
  public ResultSet executeQuery(String query)
    throws SQLException
  {

    try {
      if (getConnection() == null) {
        connect(true);
      }
    } catch (ClassNotFoundException exp) {

      if (getErrorHandler() != null)
      {
        getErrorHandler().handle(exp);
      }
      else
      {
        exp.printStackTrace(System.err);
      }
    }

    SRPair obj = getSRPair();

    if (getDebug())
      System.err.println("DbAccess.executeQuery: " + query);
    obj.resultset = obj.statement.executeQuery(query);

    return obj.resultset;
  }

  /**
   * Execute a SQL Insert/Delete/Update statement.
   * @exception java.sql.SQLException If <code>java.sql.Statement.executeUpdate()</code> failed.
   * @return The number of rows affected in this update.
   */
  public int executeUpdate(String sql)
    throws SQLException
  {

    try {
      if (getConnection() == null) {
        connect(true);
      }
    } catch (ClassNotFoundException exp) {

      if (getErrorHandler() != null)
      {
        getErrorHandler().handle(exp);
      }
      else
      {
        exp.printStackTrace(System.err);
      }
    }

    SRPair obj = getSRPair();

    if (getDebug())
      System.err.println("DbAccess.executeUpdate: " + sql);
    int val = obj.statement.executeUpdate(sql);
    obj.inuse = false;

    return val;
  }

  /**
   * The firePropertyChange method was generated to support the propertyChange field.
   */
  public void firePropertyChange(String propertyName, Object oldValue, Object newValue) {
    propertyChange.firePropertyChange(propertyName, oldValue, newValue);
  }

  /**
   * Get the connection property.
   * @return The JDBC Connection object.
   */
  public Connection getConnection() {
    return conn;
  }

  /**
   * Gets the debug property (boolean) value.
   * @return The debug property value.
   * @see #setDebug
   */
  public boolean getDebug() {
    /* Returns the debug property value. */
    return fieldDebug;
  }

  /**
   * Get the driver property.
   * @return The JDBC driver class string.
   */
  public String getDriver() {
    return driver;
  }

  /**
   * Gets the errorHandler property (org.dbgen.support.Handler) value.
   * @return The errorHandler property value.
   * @see #setErrorHandler
   */
  public Handler getErrorHandler() {
    /* Returns the errorHandler property value. */
    return fieldErrorHandler;
  }

  /**
   * Get the password property.
   * @return The password for database connection.
   */
  public String getPassword() {
    return password;
  }

  private synchronized SRPair getSRPair()
    throws SQLException
  {
    SRPair obj;
    int len = srs.size();

    // search for available statement.
    for (int i = 0; i < len; i++) {
      obj = (SRPair) srs.elementAt(i);

      if (!obj.inuse) {
        //System.out.println("* Re-use " + obj);
        obj.inuse = true;

        return obj;
      }
    }

    // if not, create one and add to vector.
    obj = new SRPair(conn.createStatement(), null, true);

    //System.out.println("* New SRPair " + obj);
    srs.addElement(obj);

    // debug
    //    Util.println("* Statement count: " + (len+1));

    return obj;
  }

  /**
   * Get the url property.
   * @return The JDBC url string.
   */
  public String getUrl() {
    return url;
  }

  /**
   * Get the user property.
   * @return The username for database connection.
   */
  public String getUser() {
    return user;
  }

  /**
   * Check if the JDBC connection io still available.
   * @return True if the connection is still available.
   * @exception java.sql.SQLException When a SQL Exception occurred.
   */
  public boolean isConnected()
    throws SQLException
  {
    /* Test to see if the connection has been closed */
    if ((conn != null) && conn.isClosed())
      conn = null;

    /* If connection existed and it wasn't closed, then it must be good. */
    return (conn != null);
  }

  /**
   * The removePropertyChangeListener method was generated to support the propertyChange field.
   */
  public synchronized void removePropertyChangeListener(java.beans.PropertyChangeListener listener) {
    propertyChange.removePropertyChangeListener(listener);
  }

  /**
   * Set the JDBC Connection for this DbAccess object.
   * @param conn A JDBC Connection object.
   */
  public void setConnection(Connection conn) {
    this.conn = conn;

    //System.out.println("Connection set => " + conn);
  }

  /**
   * Sets the debug property (boolean) value.
   * @param debug The new value for the property.
   * @see #getDebug
   */
  public void setDebug(boolean debug) {
    fieldDebug = debug;

    return;
  }

  /**
   * Set the JDBC driver class string.
   * @param driver A JDBC driver class name.
   */
  public void setDriver(String driver) {
    this.driver = driver;
  }

  /**
   * Sets the errorHandler property (org.dbgen.support.Handler) value.
   * @param errorHandler The new value for the property.
   * @see #getErrorHandler
   */
  public void setErrorHandler(Handler errorHandler) {
    /* Get the old property value for fire property change event. */
    Handler oldValue = fieldErrorHandler;

    /* Set the errorHandler property (attribute) to the new value. */
    fieldErrorHandler = errorHandler;

    /* Fire (signal/notify) the errorHandler property change event. */
    firePropertyChange("errorHandler", oldValue, errorHandler);

    return;
  }

  /**
   * Set the password for database connection.
   * @param The password needed to connect to the database.
   */
  public void setPassword(String password) {
    this.password = password;
  }

  /**
   * Set the JDBC url string.
   * @param A JDBC URL string.
   */
  public void setUrl(String url) {
    this.url = url;
  }

  /**
   * Set the username for database connection.
   * @param The user name needed to connect to the database.
   */
  public void setUser(String user) {
    this.user = user;
  }
}