[杂七杂八] 数据库连接池Datasource

在三层架构中，DAO层直接与数据库交互，首先要建立与数据库的连接，如果采用下图（a）所示，则用户每次的请求都要创建连接，用完又关闭，而数据库连接的创建和关闭需要消耗较大的资源，因此实际开发中常采用图（b）所示，在应用程序启动时创建一个包含多个Connection对象的连接池，DAO层使用时直接从池子里取一个Connection对象，用完后放回池子，避免了重复创建关闭数据库连接造成的开销。

2、编程实现

Datasource适配器

package jdbc;import javax.sql.DataSource;import java.io.PrintWriter;import java.sql.Connection;import java.sql.SQLException;import java.sql.SQLFeatureNotSupportedException;import java.util.logging.Logger;/** * 类似于DataSource适配器 */public abstract class BaseDataSource implements DataSource{	public Connection getConnection() throws SQLException {		return null;	}	public Connection getConnection(String username, String password) throws SQLException {		return null;	}	public <T> T unwrap(Class<T> iface) throws SQLException {		return null;	}	public boolean isWrapperFor(Class<?> iface) throws SQLException {		return false;	}	public PrintWriter getLogWriter() throws SQLException {		return null;	}	public void setLogWriter(PrintWriter out) throws SQLException {	}	public void setLoginTimeout(int seconds) throws SQLException {	}	public int getLoginTimeout() throws SQLException {		return 0;	}	public Logger getParentLogger() throws SQLFeatureNotSupportedException {		return null;	}} 

  自定义数据源

package jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;/** * 自定义数据源 */public class MyDataSource extends BaseDataSource {	private ConnectionPool pool = null ;	private static int MAX = 5 ;	public MyDataSource(){		pool = new ConnectionPool();		initPool() ;	}	/**	 * 初始化连接池	 */	private void initPool() {		try {			String driverClass = "com.mysql.jdbc.Driver" ;			String url = "jdbc:mysql://localhost:3306/big6" ;			String username= "root" ;			String password = "root" ;			Class.forName(driverClass);			for(int i = 0 ; i < MAX ; i ++){				//原生mysql连接				Connection conn = DriverManager.getConnection(url,username,password);				MyConnection myconn = new MyConnection(conn,pool) ;				pool.addConnection(myconn);			}		} catch (Exception e) {			e.printStackTrace();		}	}	/**	 * 获得连接	 */	public Connection getConnection() throws SQLException {		return pool.getConnection() ;	}}

连接池

package jdbc;import java.sql.Connection;import java.util.ArrayList;import java.util.List;/** * 连接池 */public class ConnectionPool {	//集合	private static List<Connection> list = new ArrayList<Connection>();	public synchronized Connection getConnection(){		while(list.isEmpty()){			try {				wait();			} catch (InterruptedException e) {				e.printStackTrace();			}		}		return list.remove(0);	}	/**	 * 添加连接	 */	public synchronized void addConnection(Connection conn){		list.add(conn) ;		notifyAll();	}}

连接适配器

package jdbc;import java.sql.*;import java.util.Map;import java.util.Properties;import java.util.concurrent.Executor;/** * 连接适配器 */public abstract class ConnectionAdaptor implements Connection {	public Statement createStatement() throws SQLException {		return null;	}	public PreparedStatement prepareStatement(String sql) throws SQLException {		return null;	}	public CallableStatement prepareCall(String sql) throws SQLException {		return null;	}	public String nativeSQL(String sql) throws SQLException {		return null;	}	public void setAutoCommit(boolean autoCommit) throws SQLException {	}	public boolean getAutoCommit() throws SQLException {		return false;	}	public void commit() throws SQLException {	}	public void rollback() throws SQLException {	}	public void close() throws SQLException {	}	public boolean isClosed() throws SQLException {		return false;	}	public DatabaseMetaData getMetaData() throws SQLException {		return null;	}	public void setReadOnly(boolean readOnly) throws SQLException {	}	public boolean isReadOnly() throws SQLException {		return false;	}	public void setCatalog(String catalog) throws SQLException {	}	public String getCatalog() throws SQLException {		return null;	}	public void setTransactionIsolation(int level) throws SQLException {	}	public int getTransactionIsolation() throws SQLException {		return 0;	}	public SQLWarning getWarnings() throws SQLException {		return null;	}	public void clearWarnings() throws SQLException {	}	public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {		return null;	}	public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {		return null;	}	public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {		return null;	}	public Map<String, Class<?>> getTypeMap() throws SQLException {		return null;	}	public void setTypeMap(Map<String, Class<?>> map) throws SQLException {	}	public void setHoldability(int holdability) throws SQLException {	}	public int getHoldability() throws SQLException {		return 0;	}	public Savepoint setSavepoint() throws SQLException {		return null;	}	public Savepoint setSavepoint(String name) throws SQLException {		return null;	}	public void rollback(Savepoint savepoint) throws SQLException {	}	public void releaseSavepoint(Savepoint savepoint) throws SQLException {	}	public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {		return null;	}	public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {		return null;	}	public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {		return null;	}	public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {		return null;	}	public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {		return null;	}	public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {		return null;	}	public Clob createClob() throws SQLException {		return null;	}	public Blob createBlob() throws SQLException {		return null;	}	public NClob createNClob() throws SQLException {		return null;	}	public SQLXML createSQLXML() throws SQLException {		return null;	}	public boolean isValid(int timeout) throws SQLException {		return false;	}	public void setClientInfo(String name, String value) throws SQLClientInfoException {	}	public void setClientInfo(Properties properties) throws SQLClientInfoException {	}	public String getClientInfo(String name) throws SQLException {		return null;	}	public Properties getClientInfo() throws SQLException {		return null;	}	public Array createArrayOf(String typeName, Object[] elements) throws SQLException {		return null;	}	public Struct createStruct(String typeName, Object[] attributes) throws SQLException {		return null;	}	public void setSchema(String schema) throws SQLException {	}	public String getSchema() throws SQLException {		return null;	}	public void abort(Executor executor) throws SQLException {	}	public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {	}	public int getNetworkTimeout() throws SQLException {		return 0;	}	public <T> T unwrap(Class<T> iface) throws SQLException {		return null;	}	public boolean isWrapperFor(Class<?> iface) throws SQLException {		return false;	}}

连接装饰类

package jdbc;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.SQLException;import java.sql.Statement;/** * 连接装饰类 */public class MyConnection extends ConnectionAdaptor{	//原生的mysql连接	private Connection conn ;	private ConnectionPool pool ;	public MyConnection(Connection conn , ConnectionPool pool){		this.conn = conn ;		this.pool = pool ;	}	public Statement createStatement() throws SQLException {		return conn.createStatement();	}	public PreparedStatement prepareStatement(String sql) throws SQLException {		return conn.prepareStatement(sql);	}	public void setAutoCommit(boolean autoCommit) throws SQLException {		conn.setAutoCommit(autoCommit);	}	public void commit() throws SQLException {		conn.commit();	}	public void rollback() throws SQLException {		conn.rollback();	}	public void close() throws SQLException {		pool.addConnection(this);	}}

测试

package jdbc;import javax.sql.DataSource;import java.sql.Connection;import java.sql.Statement;/** */public class TestPool {	public static void main(String[] args) throws Exception {		//创建数据源对象		DataSource ds = new MyDataSource();		//得到连接(自定义)		Connection conn = ds.getConnection();		conn.setAutoCommit(true) ;		//		Statement st = conn.createStatement();		st.execute("insert into customers(name,age) values('uu',8)") ;		st.close();		conn.close();		System.out.println("xxx");	}}