1. 数据库连接实际上是客户端和远程数据库服务器建立了一个socket连接, 创建过程比较耗性能和时间, 因此出现了数据库连接池技术。
2. 数据库连接池负责分配、管理和释放数据库连接, 它允许应用程序重复使用一个现有的数据库连接，而不是再重新建立一个。这项技术能明显提高对数据库操作的性能。
3. 连接池基本的思想是在系统初始化的时候, 将数据库连接作为对象存储在内存中, 当用户需要访问数据库时, 并非建立一个新的连接, 而是从连接池中取出一个已建立的空闲连接对象。使用完毕后, 用户也并非将连接关闭, 而是将连接放回连接池中, 以供下一个请求访问使用。而连接的建立、断开都由连接池自身来管理。同时, 还可以通过设置连接池的参数来控制连接池中的初始连接数、连接的上下限数以及每个连接的最大使用次数、最大空闲时间等等。也可以通过其自身的管理机制来监视数据库连接的数量、使用情况等。
4. 在Java中常用的开源的数据库连接池有以下几种
4.1. C3P0: 是一个开放源代码的JDBC连接池, 包括了实现jdbc3和jdbc2扩展规范说明的Connection和Statement池的DataSources 对象。
4.2. Proxool: 是一个Java SQL Driver驱动程序, 提供了对选择的其它类型的驱动程序的连接池封装。可以非常简单的移植到现存的代码中, 完全可配置, 快速、成熟、健壮。可以透明地为现存的JDBC驱动程序增加连接池功能。
4.3. Jakarta DBCP: DBCP是一个依赖Jakartacommons-pool对象池机制的数据库连接池。DBCP可以直接的在应用程序中使用。
4.4. 目前Proxool和DBCP以及C3P0一起, 最为常见的三种JDBC连接池技术。
4.5. 后来, Hibernate官方宣布由于Bug太多不再支持DBCP, 而推荐使用C3P0或Proxool。
5. 自己实现Java的数据库连接池接口(DataSource)
5.1. 创建一个名称为SunDataSource的Java工程, 使用之前的JDBCUtil.java和jdbc.properties属性文件
5.2. 创建一个MyDataSource.java实现Java的DataSource接口
package com.lywgames.myjdbc;import java.io.PrintWriter;import java.sql.Connection;import java.sql.SQLException;import java.sql.SQLFeatureNotSupportedException;import java.util.ArrayList;import java.util.List;import java.util.logging.Logger;import javax.sql.DataSource;import com.lywgames.util.JDBCUtil;/*** 实现java的DataSource接口*/public class MyDataSource implements DataSource {private List<Connection> list = new ArrayList<Connection>();/*** 对象一创建就创建10个数据库连接对象, 放到list对象*/public MyDataSource() {for (int i = 0; i < 10; i++) {Connection conn = JDBCUtil.getConn();list.add(conn);}}// 该连接池对外公布的获取连接的方法@Overridepublic Connection getConnection() throws SQLException {// 发现连接池的连接数量为0, 自动扩容if(list.size() == 0) {for (int i = 0; i < 10; i++) {Connection conn = JDBCUtil.getConn();list.add(conn);}}return list.remove(0);}/*** 归还数据库连接对象* @param conn*/public void backConnection(Connection conn) {System.out.println("归还连接前, 连接数:" + list.size());list.add(conn);System.out.println("归还连接后, 连接数:" + list.size());}@Overridepublic Connection getConnection(String username, String password) throws SQLException {return null;}@Overridepublic PrintWriter getLogWriter() throws SQLException {return null;}@Overridepublic int getLoginTimeout() throws SQLException {return 0;}@Overridepublic Logger getParentLogger() throws SQLFeatureNotSupportedException {return null;}@Overridepublic void setLogWriter(PrintWriter arg0) throws SQLException {}@Overridepublic void setLoginTimeout(int arg0) throws SQLException {}@Overridepublic boolean isWrapperFor(Class<?> arg0) throws SQLException {return false;}@Overridepublic <T> T unwrap(Class<T> arg0) throws SQLException {return null;}}
5.3. 使用MyDataSource
package com.lywgames.myjdbc;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.SQLException;import java.sql.Timestamp;import com.lywgames.util.JDBCUtil;public class MyJDBC {public static void main(String[] args) {Connection conn = null;PreparedStatement ps = null;// 创建自己的连接池对象MyDataSource ds = new MyDataSource();try {conn = ds.getConnection();ps = conn.prepareStatement("insert into user values(null,?,?,?)");ps.setString(1, "lvbu");ps.setString(2, "123456");ps.setTimestamp(3, new Timestamp(System.currentTimeMillis()));ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();} finally {JDBCUtil.release(ps);}// 归还连接ds.backConnection(conn);}}
5.4. 运行程序, 查看结果
6. 对连接进行包装
6.1. 创建一个名称为MyDataSourceConnectionWrap的Java工程, 使用之前的JDBCUtil.java和jdbc.properties属性文件
6.2. 创建一个ConnectionWrap.java实现Connection接口
package com.lywgames.myjdbc;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;/*** 使用使用装饰者模式, 对JDBC实际创建的Connection对象进行包装*/public class ConnectionWrap implements Connection {private List<Connection> list;private Connection connection;public ConnectionWrap(Connection connection, List<Connection> list) {this.connection = connection;this.list = list;}// 在Connection对象的close方法里归还数据库连接@Overridepublic void close() throws SQLException {System.out.println("调用close方法归还连接前: " + list.size());this.list.add(connection);System.out.println("调用close方法归还连接后: " + list.size());}@Overridepublic PreparedStatement prepareStatement(String sql) throws SQLException {return connection.prepareStatement(sql);}@Overridepublic PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {return null;}@Overridepublic PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {return null;}@Overridepublic PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {return null;}@Overridepublic PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return null;}@Overridepublic PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency,int resultSetHoldability) throws SQLException {return null;}@Overridepublic boolean isWrapperFor(Class<?> arg0) throws SQLException {return false;}@Overridepublic <T> T unwrap(Class<T> arg0) throws SQLException {return null;}@Overridepublic void abort(Executor executor) throws SQLException {}@Overridepublic void clearWarnings() throws SQLException {}@Overridepublic void commit() throws SQLException {}@Overridepublic Array createArrayOf(String typeName, Object[] elements) throws SQLException {return null;}@Overridepublic Blob createBlob() throws SQLException {return null;}@Overridepublic Clob createClob() throws SQLException {return null;}@Overridepublic NClob createNClob() throws SQLException {return null;}@Overridepublic SQLXML createSQLXML() throws SQLException {return null;}@Overridepublic Statement createStatement() throws SQLException {return null;}@Overridepublic Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {return null;}@Overridepublic Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return null;}@Overridepublic Struct createStruct(String typeName, Object[] attributes) throws SQLException {return null;}@Overridepublic boolean getAutoCommit() throws SQLException {return false;}@Overridepublic String getCatalog() throws SQLException {return null;}@Overridepublic Properties getClientInfo() throws SQLException {return null;}@Overridepublic String getClientInfo(String name) throws SQLException {return null;}@Overridepublic int getHoldability() throws SQLException {return 0;}@Overridepublic DatabaseMetaData getMetaData() throws SQLException {return null;}@Overridepublic int getNetworkTimeout() throws SQLException {return 0;}@Overridepublic String getSchema() throws SQLException {return null;}@Overridepublic int getTransactionIsolation() throws SQLException {return 0;}@Overridepublic Map<String, Class<?>> getTypeMap() throws SQLException {return null;}@Overridepublic SQLWarning getWarnings() throws SQLException {return null;}@Overridepublic boolean isClosed() throws SQLException {return false;}@Overridepublic boolean isReadOnly() throws SQLException {return false;}@Overridepublic boolean isValid(int timeout) throws SQLException {return false;}@Overridepublic String nativeSQL(String sql) throws SQLException {return null;}@Overridepublic CallableStatement prepareCall(String sql) throws SQLException {return null;}@Overridepublic CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return null;}@Overridepublic CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency,int resultSetHoldability) throws SQLException {return null;}@Overridepublic void releaseSavepoint(Savepoint savepoint) throws SQLException {}@Overridepublic void rollback() throws SQLException {}@Overridepublic void rollback(Savepoint savepoint) throws SQLException {}@Overridepublic void setAutoCommit(boolean autoCommit) throws SQLException {}@Overridepublic void setCatalog(String catalog) throws SQLException {}@Overridepublic void setClientInfo(Properties properties) throws SQLClientInfoException {}@Overridepublic void setClientInfo(String name, String value) throws SQLClientInfoException {}@Overridepublic void setHoldability(int holdability) throws SQLException {}@Overridepublic void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {}@Overridepublic void setReadOnly(boolean readOnly) throws SQLException {}@Overridepublic Savepoint setSavepoint() throws SQLException {return null;}@Overridepublic Savepoint setSavepoint(String name) throws SQLException {return null;}@Overridepublic void setSchema(String schema) throws SQLException {}@Overridepublic void setTransactionIsolation(int level) throws SQLException {}@Overridepublic void setTypeMap(Map<String, Class<?>> map) throws SQLException {}}
6.3. 创建一个MyDataSource.java实现DataSource接口
package com.lywgames.myjdbc;import java.io.PrintWriter;import java.sql.Connection;import java.sql.SQLException;import java.sql.SQLFeatureNotSupportedException;import java.util.ArrayList;import java.util.List;import java.util.logging.Logger;import javax.sql.DataSource;import com.lywgames.util.JDBCUtil;/*** 实现java的DataSource接口*/public class MyDataSource implements DataSource {private List<Connection> list = new ArrayList<Connection>();/*** 对象一创建就创建10个数据库连接对象, 放到list对象*/public MyDataSource() {for (int i = 0; i < 10; i++) {list.add(JDBCUtil.getConn());}}// 该连接池对外公布的获取连接的方法@Overridepublic Connection getConnection() throws SQLException {// 发现连接池的连接数量为0, 自动扩容if(list.size() == 0) {for (int i = 0; i < 10; i++) {list.add(JDBCUtil.getConn());}}// 对之前的Connection对象进行包装Connection connectionWrap = new ConnectionWrap(list.remove(0), list);return connectionWrap;}@Overridepublic Connection getConnection(String username, String password) throws SQLException {return null;}@Overridepublic PrintWriter getLogWriter() throws SQLException {return null;}@Overridepublic int getLoginTimeout() throws SQLException {return 0;}@Overridepublic Logger getParentLogger() throws SQLFeatureNotSupportedException {return null;}@Overridepublic void setLogWriter(PrintWriter arg0) throws SQLException {}@Overridepublic void setLoginTimeout(int arg0) throws SQLException {}@Overridepublic boolean isWrapperFor(Class<?> arg0) throws SQLException {return false;}@Overridepublic <T> T unwrap(Class<T> arg0) throws SQLException {return null;}}
6.4. 使用MyDataSource
package com.lywgames.myjdbc;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.SQLException;import java.sql.Timestamp;import com.lywgames.util.JDBCUtil;public class MyJDBC {public static void main(String[] args) {Connection conn = null;PreparedStatement ps = null;// 创建自己的连接池对象MyDataSource ds = new MyDataSource();try {conn = ds.getConnection();ps = conn.prepareStatement("insert into user values(null,?,?,?)");ps.setString(1, "diaochan");ps.setString(2, "123456");ps.setTimestamp(3, new Timestamp(System.currentTimeMillis()));ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();} finally {JDBCUtil.release(conn, ps);}}}
6.5. 运行程序, 查看结果
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