传统JDBC的操作,对连接的对象销毁不是特别好。每次创建和销毁连接都是需要花费时间。可以使用连接池优化的程序。
在程序开始的时候，可以创建几个连接，将连接放入到连接池中，用户使用连接的时候，可以从连接池中进行获取。用完之后，可以将连接归还连接池。
Java为数据库连接池提供了公共的接口：javax.sql.DataSource。
根据我们对连接池简单的理解，如果我们要自定义连接池，需要完成以下步骤：
- 创建连接池实现（数据库），并实现接口javax.sql.DataSource.。因为我们只使用该接口中的getConnectoin()方法，简化本案例，我们将自己提供方法，而没有实现接口。
- 提供一个集合，用于存放连接，因为添加/移除频繁，所以选择LinkedList。
- 本案例在静态代码块中，为连接池初始化5个连接。
- 之后，如果程序需要连接，调用实现类的getConnection()，本方法将从连接池（容器List）获得连接。为了保证当前连接只能提供给一个线程使用，所以我们需要将连接先从连接池中移除。
- 当用户使用完连接，释放连接时，不执行close()方法，而是把连接归还到连接池中去。
实现示例代码 MyDataSource.java 如下：
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package cn.benz.datasource; import java.io.PrintWriter; import java.sql.Connection; import java.sql.SQLException; import java.sql.SQLFeatureNotSupportedException; import java.util.LinkedList; import java.util.logging.Logger; import javax.sql.DataSource; import cn.benz.test.JDBCUtils; public class MyDataSource implements DataSource{ //1. 创建1个容器，存储connection对象 private static LinkedList<Connection> pool = new LinkedList<Connection>(); //2. 创建5个链接到容器里去 static{ for (int i = 0; i < 5; i++) { //JDBCUtils.getConnection();是自己写的JDBC简单工具类，不是JDK提供 Connection conn = JDBCUtils.getConnection(); //把链接放到容器里 pool.add(conn); } } //继承DataSource接口，会有很多实现方法，这里我们只需要getConnection()这个方法 /** * 重写获取连接的方法 */ @Override public Connection getConnection() throws SQLException { Connection conn = null; //3. 使用前判断一下 if (pool.size() == 0) { //4. 池子里没有再创建一些 for (int i = 0; i < 5; i++) { conn = JDBCUtils.getConnection(); pool.add(conn); } } //5. 从池子里面获取一个连接对象Connection conn = pool.remove(0);//从池子里拿出一个Connection，并移除该Connection return conn; } /** * 归还Connection对象到连接池 * @param conn */ public void backConnection(Connection conn){ pool.add(conn); } @Override public PrintWriter getLogWriter() throws SQLException { // TODO Auto-generated method stub return null; } @Override public void setLogWriter(PrintWriter out) throws SQLException { // TODO Auto-generated method stub } @Override public void setLoginTimeout(int seconds) throws SQLException { // TODO Auto-generated method stub } @Override public int getLoginTimeout() throws SQLException { // TODO Auto-generated method stub return 0; } @Override public Logger getParentLogger() throws SQLFeatureNotSupportedException { // TODO Auto-generated method stub return null; } @Override public <T> T unwrap(Class<T> 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 Connection getConnection(String username, String password) throws SQLException { // TODO Auto-generated method stub return null; } } |
测试代码调用 TestMyDataSource.java：
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package cn.benz.test; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.SQLException; import org.junit.Test; import cn.benz.datasource.MyDataSource; public class TestMyDataSource { @Test public void addUser(){ Connection conn = null; PreparedStatement pstmt = null; //1. 创建自定义连接池对象 MyDataSource dataSource = new MyDataSource(); try { //2. 从池子里取出连接 conn = dataSource.getConnection(); String sql = "insert into user values(null,?,?)"; pstmt = conn.prepareStatement(sql); pstmt.setString(1, "tester"); pstmt.setString(2, "00001"); int row = pstmt.executeUpdate(); if (row >0) { System.out.println("添加成功"); }else { System.out.println("添加失败"); } } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); }finally{ //3. 归还连接 dataSource.backConnection(conn); } } } |
二、装饰者设计模式–修改close()方法
装饰者设计模式
点击这里查看装饰者设计模式
装饰者固定结构：接口A，已知实现类C，需要装饰者创建代理类B
- 创建类B，并实现接口A
- 提供类B的构造方法，参数类型为A，用于接收A接口的其他实现类（C）
- 给类B添加类型为A成员变量，用于存放A接口的其他实现类
- 增强需要的方法
- 实现不需要增强的方法，方法体重新调用成员变量存放的其他实现类对应的方法
在这里，我们的目标是修改JDBCUtils.java里的方法release()中的conn.close()，这里JDBCUtils是被修饰类（C）。
因为close()属于Connection接口（A），所以，我们创建一个装饰者类MyConnection（B）,并实现同样的接口。
在装饰类 MyConnection中，需要提供类MyConnection的构造方法，用于接收需要修改方法的必要参数，然后再去修改需要增强的方法。
装饰类 MyConnection.java
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package cn.benz.datasource; 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.LinkedList; import java.util.Map; import java.util.Properties; import java.util.concurrent.Executor; public class MyConnection implements Connection { private Connection conn = null; private LinkedList<Connection> pool = null; /** * 提供构造方法，用于接收参数 * @param conn * @param pool */ public MyConnection(Connection conn,LinkedList<Connection> pool) { this.conn =conn; this.pool = pool; } /** * 需要增强的方法 */ @Override public void close() throws SQLException { pool.add(conn); } /** * 此方法必须覆盖，否则会出现空指针错误 */ @Override public PreparedStatement prepareStatement(String sql) throws SQLException { // TODO Auto-generated method stub return conn.prepareStatement(sql); } @Override public <T> T unwrap(Class<T> 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<String, Class<?>> getTypeMap() throws SQLException { // TODO Auto-generated method stub return null; } @Override public void setTypeMap(Map<String, Class<?>> 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; } } |
使用装饰类
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package cn.benz.datasource; import java.io.PrintWriter; import java.sql.Connection; import java.sql.SQLException; import java.sql.SQLFeatureNotSupportedException; import java.util.LinkedList; import java.util.logging.Logger; import javax.sql.DataSource; import cn.benz.test.JDBCUtils; public class MyDataSource implements DataSource{ //1. 创建1个容器，存储connection对象 private static LinkedList<Connection> pool = new LinkedList<Connection>(); //2. 创建5个链接到容器里去 static{ for (int i = 0; i < 5; i++) { //JDBCUtils.getConnection();是自己写的JDBC简单工具类，不是JDK提供 Connection conn = JDBCUtils.getConnection(); MyConnection myConn = new MyConnection(conn, pool);//使用修饰类 //把链接放到容器里 pool.add(myConn); } } //继承DataSource接口，会有很多实现方法，这里我们只需要getConnection()这个方法 /** * 重写获取连接的方法 */ @Override public Connection getConnection() throws SQLException { Connection conn = null; //3. 使用前判断一下 if (pool.size() == 0) { //4. 池子里没有再创建一些 for (int i = 0; i < 5; i++) { conn = JDBCUtils.getConnection(); MyConnection myConn = new MyConnection(conn, pool);//使用修饰类 pool.add(myConn); } } //5. 从池子里面获取一个连接对象Connection conn = pool.remove(0);//从池子里拿出一个Connection，并移除该Connection return conn; } /** * 归还Connection对象到连接池 * @param conn */ public void backConnection(Connection conn){//此处不再需要 pool.add(conn); } @Override public PrintWriter getLogWriter() throws SQLException { // TODO Auto-generated method stub return null; } @Override public void setLogWriter(PrintWriter out) throws SQLException { // TODO Auto-generated method stub } @Override public void setLoginTimeout(int seconds) throws SQLException { // TODO Auto-generated method stub } @Override public int getLoginTimeout() throws SQLException { // TODO Auto-generated method stub return 0; } @Override public Logger getParentLogger() throws SQLFeatureNotSupportedException { // TODO Auto-generated method stub return null; } @Override public <T> T unwrap(Class<T> 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 Connection getConnection(String username, String password) throws SQLException { // TODO Auto-generated method stub return null; } } |
测试类
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package cn.benz.test; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.SQLException; import org.junit.Test; import cn.benz.datasource.MyDataSource; public class TestMyDataSource { @Test public void addUser(){ Connection conn = null; PreparedStatement pstmt = null; //1. 创建自定义连接池对象 MyDataSource dataSource = new MyDataSource(); try { //2. 从池子里取出连接 conn = dataSource.getConnection(); String sql = "insert into user values(null,?,?)"; pstmt = conn.prepareStatement(sql); pstmt.setString(1, "tester02"); pstmt.setString(2, "00002"); int row = pstmt.executeUpdate(); if (row >0) { System.out.println("添加成功"); }else { System.out.println("添加失败"); } } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); }finally{ //3. 归还连接 //dataSource.backConnection(conn);//之前方法 JDBCUtils.release(conn, pstmt, null);//release()方法代码并没修改，但是调用后并不执行release()下的close()， //而是执行修饰类MyConnection里的增强后的close()，即归还连接。 //因为这里的参数conn是修饰类MyConnection处理过的，如果是原来的conn， //还是会调用close()关闭连接，而不是归还。 } } } |
文章 自定义连接池 转载需要注明出处
