本文共 12989 字，大约阅读时间需要 43 分钟。

其实，在这篇文章中，我就已详细介绍过如何编写一个自己的数据库连接池了。本文只不过是再一次的重温。

一个非常简单的自定义数据库连接池

该小节只是简单模拟一个池子的概念，让大家有个对连接池有个认识。待会我们自己编写的数据库连接池因为要存放一些数据库连接，所以关于如何获取数据库连接的操作，我们就抽取到一个工具类中，例如JDBCUtil类。

package com.meimeixia.util;import java.io.InputStream;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import java.util.Properties;public class JDBCUtil {
   		static String driverClass = null;	static String url = null;	static String name = null;	static String password= null;		static{
   		try {
   			//1. 创建一个属性配置对象			Properties properties = new Properties();//			InputStream is = new FileInputStream("jdbc.properties");						//使用类加载器，去读取src底下的资源文件。			InputStream is = JDBCUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");			//导入输入流。			properties.load(is);						//读取属性			driverClass = properties.getProperty("driverClass");			url = properties.getProperty("url");			name = properties.getProperty("name");			password = properties.getProperty("password");					} catch (Exception e) {
   			e.printStackTrace();		}	}		/**	 * 获取连接对象	 * @return	 */	public static Connection getConn(){
   		Connection conn = null;		try {
   			Class.forName(driverClass);			//静态代码块 ---> 类加载了，就执行。 java.sql.DriverManager.registerDriver(new Driver());			//DriverManager.registerDriver(new com.mysql.jdbc.Driver());			//DriverManager.getConnection("jdbc:mysql://localhost/test?user=monty&password=greatsqldb");			//2. 建立连接 参数一： 协议 + 访问的数据库 ， 参数二： 用户名 ， 参数三： 密码。			conn = DriverManager.getConnection(url, name, password);		} catch (Exception e) {
   			e.printStackTrace();		}		return conn;	}		/**	 * 释放资源	 * @param conn	 * @param st	 * @param rs	 */	public static void release(Connection conn , Statement st , ResultSet rs){
   		closeRs(rs);		closeSt(st);		closeConn(conn);	}	public static void release(Connection conn , Statement st){
   		closeSt(st);		closeConn(conn);	}		private static void closeRs(ResultSet rs){
   		try {
   			if(rs != null){
   				rs.close();			}		} catch (SQLException e) {
   			e.printStackTrace();		}finally{
   			rs = null;		}	}		private static void closeSt(Statement st){
   		try {
   			if(st != null){
   				st.close();			}		} catch (SQLException e) {
   			e.printStackTrace();		}finally{
   			st = null;		}	}		private static void closeConn(Connection conn){
   		try {
   			if(conn != null){
   				conn.close();			}		} catch (SQLException e) {
   			e.printStackTrace();		}finally{
   			conn = null;		}	}}

接着，正式来编写我们自己的数据库连接池。一开始先往池子里面放10个连接，即开始就创建10个连接，来的程序可以通过getConnection方法获取连接，用完之后，使用addBack方法归还连接，而且，记得还要扩容。

package com.meimeixia.util;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.SQLException;import javax.sql.DataSource;import org.junit.Test;public class TestPool {
   	@Test	public void testPool() {
   		Connection conn = null;		PreparedStatement ps = null;		MyDataSource dataSource = new MyDataSource();				try {
   			conn = dataSource.getConnection();						String sql = "insert into account values(NULL,'xilali',10)";			ps = conn.prepareStatement(sql);			ps.executeUpdate();		} catch (SQLException e) {
   			e.printStackTrace();		} finally {
   			try {
   				ps.close();			} catch (SQLException e) {
   				e.printStackTrace();			}			//归还连接			//conn.close();			dataSource.addBack(conn);			//JDBCUtil.release(conn, ps);		}			}	}

自定义数据库连接池出现的问题

以上自定义数据库连接池出现了如下一些问题：

• 对象没有做成单例的。在哪里使用，都需要new MyDataSource()，这就会造成有多个对象的情况出现，那就不只一个池子了；

• 需要额外记住addBack这个方法。sun公司定义的数据库连接池里面并没有这个addBack方法，所以谁需要用我们这个连接池，就需要记住这个方法是用来回收连接对象的；

• 无法面向接口编程。由于我们的连接池直接定义成了一个类，并且里面还额外添加了一个addBack方法，这就造成了我们无法面向接口编程。即我们再也不能编写如下代码了：

  DataSource dataSource = new MyDataSource();//因为DataSource接口里面没有定义addBack方法

解决自定义数据库连接池出现的问题

怎么解决以上那些问题呢？这里以addBack方法为切入点。由于多了一个addBack方法，所以使用这个连接池的地方，需要额外记住这个方法，并且还不能面向接口编程。我们不打算添加addBack方法，而是扩展原来的close方法。让close方法不关闭连接，而是把连接对象归还给池子。要想实现这个需求，有以下几种方式：

• 直接修改JDBC里面的那个Connection接口的具体实现，让它的close方法别关闭连接，而是变成回收连接对象。答案是无法办到，因为咱们没办法修改人家的源代码；
• 既然不能直接修改，那么我们改成自己定义一个类，然后继承那个Connection接口的实现类，然后在它的close方法基础上，加入我们的回收逻辑。答案也是无法办到，因为我们根本不知道Connection接口的实现类是哪一个；
• 使用装饰者模式来实现；
• 使用动态代理技术，拦截你对真实业务对象的访问，采用拦截的方式进行增强，这也是终极解决方案。例如Spring AOP（向切面编程）。

下面，我们就以装饰者模式来改进上面编写的自定义数据库连接池。首先，编写一个ConnectionWrap包装类来继承Connection接口。

package com.meimeixia.util;import java.sql.Array;import java.sql.Blob;import java.sql.CallableStatement;import java.sql.Clob;import java.sql.Connection;import java.sql.DatabaseMetaData;import java.sql.NClob;import java.sql.PreparedStatement;import java.sql.SQLClientInfoException;import java.sql.SQLException;import java.sql.SQLWarning;import java.sql.SQLXML;import java.sql.Savepoint;import java.sql.Statement;import java.sql.Struct;import java.util.List;import java.util.Map;import java.util.Properties;import java.util.concurrent.Executor;public class ConnectionWrap implements Connection {
   		Connection connection = null;	List
   
     list;	public ConnectionWrap(Connection connection, List
    
      list) {
   		super();		this.connection = connection;		this.list = list;	}	@Override	public void close() throws SQLException {
   		//connection.close();		System.out.println("有人来归还连接对象了，归还之前，池子里面是：" + list.size());		list.add(connection);		System.out.println("有人来归还连接对象了，归还之后...，池子里面是：" + list.size());	}		@Override	public PreparedStatement prepareStatement(String sql) throws SQLException {
   		return connection.prepareStatement(sql);	}	@Override	public 
     
       T unwrap(Class
      
        iface) throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public boolean isWrapperFor(Class
        iface) throws SQLException {
   		// TODO Auto-generated method stub		return false;	}	@Override	public Statement createStatement() throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public CallableStatement prepareCall(String sql) throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public String nativeSQL(String sql) throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public void setAutoCommit(boolean autoCommit) throws SQLException {
   		// TODO Auto-generated method stub			}	@Override	public boolean getAutoCommit() throws SQLException {
   		// TODO Auto-generated method stub		return false;	}	@Override	public void commit() throws SQLException {
   		// TODO Auto-generated method stub			}	@Override	public void rollback() throws SQLException {
   		// TODO Auto-generated method stub			}		@Override	public boolean isClosed() throws SQLException {
   		// TODO Auto-generated method stub		return false;	}	@Override	public DatabaseMetaData getMetaData() throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public void setReadOnly(boolean readOnly) throws SQLException {
   		// TODO Auto-generated method stub			}	@Override	public boolean isReadOnly() throws SQLException {
   		// TODO Auto-generated method stub		return false;	}	@Override	public void setCatalog(String catalog) throws SQLException {
   		// TODO Auto-generated method stub			}	@Override	public String getCatalog() throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public void setTransactionIsolation(int level) throws SQLException {
   		// TODO Auto-generated method stub			}	@Override	public int getTransactionIsolation() throws SQLException {
   		// TODO Auto-generated method stub		return 0;	}	@Override	public SQLWarning getWarnings() throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public void clearWarnings() throws SQLException {
   		// TODO Auto-generated method stub			}	@Override	public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency)			throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public Map
       
        > getTypeMap() throws SQLException {
   		// TODO Auto-generated method stub		return null;	}	@Override	public void setTypeMap(Map
        
         > map) throws SQLException { // TODO Auto-generated method stub } @Override public void setHoldability(int holdability) throws SQLException { // TODO Auto-generated method stub } @Override public int getHoldability() throws SQLException { // TODO Auto-generated method stub return 0; } @Override public Savepoint setSavepoint() throws SQLException { // TODO Auto-generated method stub return null; } @Override public Savepoint setSavepoint(String name) throws SQLException { // TODO Auto-generated method stub return null; } @Override public void rollback(Savepoint savepoint) throws SQLException { // TODO Auto-generated method stub } @Override public void releaseSavepoint(Savepoint savepoint) throws SQLException { // TODO Auto-generated method stub } @Override public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { // TODO Auto-generated method stub return null; } @Override public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { // TODO Auto-generated method stub return null; } @Override public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { // TODO Auto-generated method stub return null; } @Override public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException { // TODO Auto-generated method stub return null; } @Override public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException { // TODO Auto-generated method stub return null; } @Override public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException { // TODO Auto-generated method stub return null; } @Override public Clob createClob() throws SQLException { // TODO Auto-generated method stub return null; } @Override public Blob createBlob() throws SQLException { // TODO Auto-generated method stub return null; } @Override public NClob createNClob() throws SQLException { // TODO Auto-generated method stub return null; } @Override public SQLXML createSQLXML() throws SQLException { // TODO Auto-generated method stub return null; } @Override public boolean isValid(int timeout) throws SQLException { // TODO Auto-generated method stub return false; } @Override public void setClientInfo(String name, String value) throws SQLClientInfoException { // TODO Auto-generated method stub } @Override public void setClientInfo(Properties properties) throws SQLClientInfoException { // TODO Auto-generated method stub } @Override public String getClientInfo(String name) throws SQLException { // TODO Auto-generated method stub return null; } @Override public Properties getClientInfo() throws SQLException { // TODO Auto-generated method stub return null; } @Override public Array createArrayOf(String typeName, Object[] elements) throws SQLException { // TODO Auto-generated method stub return null; } @Override public Struct createStruct(String typeName, Object[] attributes) throws SQLException { // TODO Auto-generated method stub return null; } @Override public void setSchema(String schema) throws SQLException { // TODO Auto-generated method stub } @Override public String getSchema() throws SQLException { // TODO Auto-generated method stub return null; } @Override public void abort(Executor executor) throws SQLException { // TODO Auto-generated method stub } @Override public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException { // TODO Auto-generated method stub } @Override public int getNetworkTimeout() throws SQLException { // TODO Auto-generated method stub return 0; } }
        
       
      
     
    
   

紧接着，改进我们自定义的数据库连接池。这里，我并没有使用单例模式来设计该类，实际上，这里应使用单例模式。

package com.meimeixia.util;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.SQLException;import javax.sql.DataSource;import org.junit.Test;public class TestPool {
   	@Test	public void testPool() {
   		Connection conn = null;		PreparedStatement ps = null;		MyDataSource dataSource = new MyDataSource();				try {
   			conn = dataSource.getConnection();						String sql = "insert into account values(NULL,'xilali',10)";			ps = conn.prepareStatement(sql);			ps.executeUpdate();		} catch (SQLException e) {
   			e.printStackTrace();		} finally {
   			try {
   				ps.close();			} catch (SQLException e) {
   				e.printStackTrace();			}			//归还连接			//conn.close();			//dataSource.addBack(conn);			JDBCUtil.release(conn, ps);		}			}	}

转载地址：https://liayun.blog.csdn.net/article/details/94969231 如侵犯您的版权，请留言回复原文章的地址，我们会给您删除此文章，给您带来不便请您谅解！