Spring Framework example source code file (SingleConnectionDataSource.java)

This example Spring Framework source code file (SingleConnectionDataSource.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Spring Framework tags/keywords

boolean, cannotgetjdbcconnectionexception, closesuppressinginvocationhandler, connection, connection, jdbc, jdbc, object, reflection, singleconnectiondatasource, singleconnectiondatasource, sql, sqlexception, sqlexception, string, string, throwable

The Spring Framework SingleConnectionDataSource.java source code

/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jdbc.datasource;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.SQLException;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.jdbc.CannotGetJdbcConnectionException;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

/**
 * Implementation of {@link SmartDataSource} that wraps a single JDBC Connection
 * which is not closed after use. Obviously, this is not multi-threading capable.
 *
 * <p>Note that at shutdown, someone should close the underlying Connection
 * via the <code>close() method. Client code will never call close
 * on the Connection handle if it is SmartDataSource-aware (e.g. uses
 * <code>DataSourceUtils.releaseConnection).
 *
 * <p>If client code will call close() in the assumption of a pooled
 * Connection, like when using persistence tools, set "suppressClose" to "true".
 * This will return a close-suppressing proxy instead of the physical Connection.
 * Be aware that you will not be able to cast this to a native
 * <code>OracleConnection or the like anymore; you need to use a
 * {@link org.springframework.jdbc.support.nativejdbc.NativeJdbcExtractor} then.
 *
 * <p>This is primarily intended for testing. For example, it enables easy testing
 * outside an application server, for code that expects to work on a DataSource.
 * In contrast to {@link DriverManagerDataSource}, it reuses the same Connection
 * all the time, avoiding excessive creation of physical Connections.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see #getConnection()
 * @see java.sql.Connection#close()
 * @see DataSourceUtils#releaseConnection
 * @see org.springframework.jdbc.support.nativejdbc.NativeJdbcExtractor
 */
public class SingleConnectionDataSource extends DriverManagerDataSource
		implements SmartDataSource, DisposableBean {

	/** Create a close-suppressing proxy? */
	private boolean suppressClose;

	/** Override AutoCommit? */
	private Boolean autoCommit;

	/** Wrapped Connection */
	private Connection target;

	/** Proxy Connection */
	private Connection connection;

	/** Synchronization monitor for the shared Connection */
	private final Object connectionMonitor = new Object();


	/**
	 * Constructor for bean-style configuration.
	 */
	public SingleConnectionDataSource() {
	}

	/**
	 * Create a new SingleConnectionDataSource with the given standard
	 * DriverManager parameters.
	 * @param driverClassName the JDBC driver class name
	 * @param url the JDBC URL to use for accessing the DriverManager
	 * @param username the JDBC username to use for accessing the DriverManager
	 * @param password the JDBC password to use for accessing the DriverManager
	 * @param suppressClose if the returned Connection should be a
	 * close-suppressing proxy or the physical Connection
	 * @see java.sql.DriverManager#getConnection(String, String, String)
	 */
	public SingleConnectionDataSource(
			String driverClassName, String url, String username, String password, boolean suppressClose)
			throws CannotGetJdbcConnectionException {

		super(driverClassName, url, username, password);
		this.suppressClose = suppressClose;
	}

	/**
	 * Create a new SingleConnectionDataSource with the given standard
	 * DriverManager parameters.
	 * @param url the JDBC URL to use for accessing the DriverManager
	 * @param username the JDBC username to use for accessing the DriverManager
	 * @param password the JDBC password to use for accessing the DriverManager
	 * @param suppressClose if the returned Connection should be a
	 * close-suppressing proxy or the physical Connection
	 * @see java.sql.DriverManager#getConnection(String, String, String)
	 */
	public SingleConnectionDataSource(String url, String username, String password, boolean suppressClose)
			throws CannotGetJdbcConnectionException {

		super(url, username, password);
		this.suppressClose = suppressClose;
	}

	/**
	 * Create a new SingleConnectionDataSource with the given standard
	 * DriverManager parameters.
	 * @param url the JDBC URL to use for accessing the DriverManager
	 * @param suppressClose if the returned Connection should be a
	 * close-suppressing proxy or the physical Connection
	 * @see java.sql.DriverManager#getConnection(String, String, String)
	 */
	public SingleConnectionDataSource(String url, boolean suppressClose)
			throws CannotGetJdbcConnectionException {

		super(url);
		this.suppressClose = suppressClose;
	}

	/**
	 * Create a new SingleConnectionDataSource with a given Connection.
	 * @param target underlying target Connection
	 * @param suppressClose if the Connection should be wrapped with a Connection that
	 * suppresses <code>close() calls (to allow for normal close()
	 * usage in applications that expect a pooled Connection but do not know our
	 * SmartDataSource interface)
	 */
	public SingleConnectionDataSource(Connection target, boolean suppressClose) {
		Assert.notNull(target, "Connection must not be null");
		this.target = target;
		this.suppressClose = suppressClose;
		this.connection = (suppressClose ? getCloseSuppressingConnectionProxy(target) : target);
	}


	/**
	 * Set whether the returned Connection should be a close-suppressing proxy
	 * or the physical Connection.
	 */
	public void setSuppressClose(boolean suppressClose) {
		this.suppressClose = suppressClose;
	}

	/**
	 * Return whether the returned Connection will be a close-suppressing proxy
	 * or the physical Connection.
	 */
	protected boolean isSuppressClose() {
		return this.suppressClose;
	}

	/**
	 * Set whether the returned Connection's "autoCommit" setting should be overridden.
	 */
	public void setAutoCommit(boolean autoCommit) {
		this.autoCommit = (autoCommit ? Boolean.TRUE : Boolean.FALSE);
	}

	/**
	 * Return whether the returned Connection's "autoCommit" setting should be overridden.
	 * @return the "autoCommit" value, or <code>null if none to be applied
	 */
	protected Boolean getAutoCommitValue() {
		return this.autoCommit;
	}


	public Connection getConnection() throws SQLException {
		synchronized (this.connectionMonitor) {
			if (this.connection == null) {
				// No underlying Connection -> lazy init via DriverManager.
				initConnection();
			}
			if (this.connection.isClosed()) {
				throw new SQLException(
						"Connection was closed in SingleConnectionDataSource. Check that user code checks " +
						"shouldClose() before closing Connections, or set 'suppressClose' to 'true'");
			}
			return this.connection;
		}
	}

	/**
	 * Specifying a custom username and password doesn't make sense
	 * with a single Connection. Returns the single Connection if given
	 * the same username and password; throws a SQLException else.
	 */
	public Connection getConnection(String username, String password) throws SQLException {
		if (ObjectUtils.nullSafeEquals(username, getUsername()) &&
				ObjectUtils.nullSafeEquals(password, getPassword())) {
			return getConnection();
		}
		else {
			throw new SQLException("SingleConnectionDataSource does not support custom username and password");
		}
	}

	/**
	 * This is a single Connection: Do not close it when returning to the "pool".
	 */
	public boolean shouldClose(Connection con) {
		synchronized (this.connectionMonitor) {
			return (con != this.connection && con != this.target);
		}
	}

	/**
	 * Close the underlying Connection.
	 * The provider of this DataSource needs to care for proper shutdown.
	 * <p>As this bean implements DisposableBean, a bean factory will
	 * automatically invoke this on destruction of its cached singletons.
	 */
	public void destroy() {
		synchronized (this.connectionMonitor) {
			closeConnection();
		}
	}


	/**
	 * Initialize the underlying Connection via the DriverManager.
	 */
	public void initConnection() throws SQLException {
		if (getUrl() == null) {
			throw new IllegalStateException("'url' property is required for lazily initializing a Connection");
		}
		synchronized (this.connectionMonitor) {
			closeConnection();
			this.target = getConnectionFromDriverManager();
			prepareConnection(this.target);
			if (logger.isInfoEnabled()) {
				logger.info("Established shared JDBC Connection: " + this.target);
			}
			this.connection = (isSuppressClose() ? getCloseSuppressingConnectionProxy(this.target) : this.target);
		}
	}

	/**
	 * Reset the underlying shared Connection, to be reinitialized on next access.
	 */
	public void resetConnection() {
		synchronized (this.connectionMonitor) {
			closeConnection();
			this.target = null;
			this.connection = null;
		}
	}

	/**
	 * Prepare the given Connection before it is exposed.
	 * <p>The default implementation applies the auto-commit flag, if necessary.
	 * Can be overridden in subclasses.
	 * @param con the Connection to prepare
	 * @see #setAutoCommit
	 */
	protected void prepareConnection(Connection con) throws SQLException {
		Boolean autoCommit = getAutoCommitValue();
		if (autoCommit != null && con.getAutoCommit() != autoCommit.booleanValue()) {
			con.setAutoCommit(autoCommit.booleanValue());
		}
	}

	/**
	 * Close the underlying shared Connection.
	 */
	private void closeConnection() {
		if (this.target != null) {
			try {
				this.target.close();
			}
			catch (Throwable ex) {
				logger.warn("Could not close shared JDBC Connection", ex);
			}
		}
	}

	/**
	 * Wrap the given Connection with a proxy that delegates every method call to it
	 * but suppresses close calls.
	 * @param target the original Connection to wrap
	 * @return the wrapped Connection
	 */
	protected Connection getCloseSuppressingConnectionProxy(Connection target) {
		return (Connection) Proxy.newProxyInstance(
				ConnectionProxy.class.getClassLoader(),
				new Class[] {ConnectionProxy.class},
				new CloseSuppressingInvocationHandler(target));
	}


	/**
	 * Invocation handler that suppresses close calls on JDBC Connections.
	 */
	private static class CloseSuppressingInvocationHandler implements InvocationHandler {

		private final Connection target;

		public CloseSuppressingInvocationHandler(Connection target) {
			this.target = target;
		}

		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			// Invocation on ConnectionProxy interface coming in...

			if (method.getName().equals("getTargetConnection")) {
				// Handle getTargetConnection method: return underlying Connection.
				return this.target;
			}
			else if (method.getName().equals("equals")) {
				// Only consider equal when proxies are identical.
				return (proxy == args[0] ? Boolean.TRUE : Boolean.FALSE);
			}
			else if (method.getName().equals("hashCode")) {
				// Use hashCode of Connection proxy.
				return new Integer(hashCode());
			}
			else if (method.getName().equals("close")) {
				// Handle close method: don't pass the call on.
				return null;
			}

			// Invoke method on target Connection.
			try {
				return method.invoke(this.target, args);
			}
			catch (InvocationTargetException ex) {
				throw ex.getTargetException();
			}
		}
	}

}