自定义连接池

由于jdbc操作数据库时会经常创建和销毁连接，造成资源消耗，所以引入连接池。

连接池是存储Connection对象的容器，因为要经常对这个容器操作，我们用LinkedList来存储。

之前我们关闭连接，调用close()方法，销毁Connection对象，引入连接池后，是把这个对象回收到连接池中，不是销毁。

自定义连接池要实现DataSource接口，此接口在javax.sql下，重写getConnection()方法。

自定义连接池：

package cn.sasa.pool;

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.sasa.utils.DBUtils;

//自定义连接池
//实现DataSource接口，注意是javax.sql下的DataSource
public class MyPool implements  DataSource{
    //准备一个池子用于存储Connection对象，因为要频繁操作，用LinkedList接收。
    private static LinkedList<Connection> pool = new LinkedList<Connection>();
    
    //创建连接放到池子中
    static {
        for(int i=0;i<5;i++) {
            Connection conn = DBUtils.getConnection();
            //改造conn
            MyConnection myconn = new MyConnection(conn, pool);
            pool.add(myconn);
        }
    }
    
    /**
     * 获取连接对象
     */
    @Override
    public Connection getConnection() throws SQLException {
        Connection conn = null;
        //使用前先判断有没有
        if(pool.size()==0) {
            for(int i=0;i<5;i++) {
                conn = DBUtils.getConnection();
                //改造conn
                MyConnection myconn = new MyConnection(conn, pool);
                pool.add(myconn);
            }
        }
        //获取一个连接对象
        return pool.remove(0);
    }
    
    @Override
    public Logger getParentLogger() throws SQLFeatureNotSupportedException {
        return null;
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return null;
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return false;
    }

    

    @Override
    public Connection getConnection(String username, String password) throws SQLException {
        return null;
    }

    @Override
    public PrintWriter getLogWriter() throws SQLException {
        return null;
    }

    @Override
    public void setLogWriter(PrintWriter out) throws SQLException {
    }

    @Override
    public void setLoginTimeout(int seconds) throws SQLException {
    }

    @Override
    public int getLoginTimeout() throws SQLException {
        return 0;
    }
}

包装Connection

package cn.sasa.pool;

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;

//为conn调用close()回收到连接池中
public class MyConnection implements Connection{

    private Connection conn;
    private LinkedList<Connection> pool;
    
    public MyConnection(Connection conn, LinkedList<Connection> pool) {
        this.conn = conn;
        this.pool = pool;
    }
    
    //增强close方法
    @Override
    public void close() throws SQLException {
        pool.add(conn);
    }
    
    //重写此方法，否则报空指针异常
    @Override
    public PreparedStatement prepareStatement(String sql) throws SQLException {
        return conn.prepareStatement(sql);
    }
    
    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return null;
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return false;
    }

    @Override
    public Statement createStatement() throws SQLException {
        return null;
    }

    

    @Override
    public CallableStatement prepareCall(String sql) throws SQLException {
        return null;
    }

    @Override
    public String nativeSQL(String sql) throws SQLException {
        return null;
    }

    @Override
    public void setAutoCommit(boolean autoCommit) throws SQLException {
    }

    @Override
    public boolean getAutoCommit() throws SQLException {
        return false;
    }

    @Override
    public void commit() throws SQLException {
    }

    @Override
    public void rollback() throws SQLException {
    }

    

    @Override
    public boolean isClosed() throws SQLException {
        return false;
    }

    @Override
    public DatabaseMetaData getMetaData() throws SQLException {
        return null;
    }

    @Override
    public void setReadOnly(boolean readOnly) throws SQLException {
    }

    @Override
    public boolean isReadOnly() throws SQLException {
        return false;
    }

    @Override
    public void setCatalog(String catalog) throws SQLException {
    }

    @Override
    public String getCatalog() throws SQLException {
        return null;
    }

    @Override
    public void setTransactionIsolation(int level) throws SQLException {
    }

    @Override
    public int getTransactionIsolation() throws SQLException {
        return 0;
    }

    @Override
    public SQLWarning getWarnings() throws SQLException {
        return null;
    }

    @Override
    public void clearWarnings() throws SQLException {
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency)
            throws SQLException {
        return null;
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
        return null;
    }

    @Override
    public Map<String, Class<?>> getTypeMap() throws SQLException {
        return null;
    }

    @Override
    public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
    }

    @Override
    public void setHoldability(int holdability) throws SQLException {
    }

    @Override
    public int getHoldability() throws SQLException {
        return 0;
    }

    @Override
    public Savepoint setSavepoint() throws SQLException {
        return null;
    }

    @Override
    public Savepoint setSavepoint(String name) throws SQLException {
        return null;
    }

    @Override
    public void rollback(Savepoint savepoint) throws SQLException {
    }

    @Override
    public void releaseSavepoint(Savepoint savepoint) throws SQLException {
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency,
            int resultSetHoldability) throws SQLException {
        return null;
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency,
            int resultSetHoldability) throws SQLException {
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
        return null;
    }

    @Override
    public Clob createClob() throws SQLException {
        return null;
    }

    @Override
    public Blob createBlob() throws SQLException {
        return null;
    }

    @Override
    public NClob createNClob() throws SQLException {
        return null;
    }

    @Override
    public SQLXML createSQLXML() throws SQLException {
        return null;
    }

    @Override
    public boolean isValid(int timeout) throws SQLException {
        return false;
    }

    @Override
    public void setClientInfo(String name, String value) throws SQLClientInfoException {
    }

    @Override
    public void setClientInfo(Properties properties) throws SQLClientInfoException {
    }

    @Override
    public String getClientInfo(String name) throws SQLException {
        return null;
    }

    @Override
    public Properties getClientInfo() throws SQLException {
        return null;
    }

    @Override
    public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
        return null;
    }

    @Override
    public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
        return null;
    }

    @Override
    public void setSchema(String schema) throws SQLException {
    }

    @Override
    public String getSchema() throws SQLException {
        return null;
    }

    @Override
    public void abort(Executor executor) throws SQLException {
    }

    @Override
    public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
    }

    @Override
    public int getNetworkTimeout() throws SQLException {
        return 0;
    }

}

测试：

package cn.sasa.test;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.sql.DataSource;

import cn.sasa.pool.MyPool;
import cn.sasa.utils.DBUtils;

public class TestPool {

    public static void main(String[] args) {
        
        //自定义连接池，使用增强close()
        Connection conn = null;
        PreparedStatement pstate = null;
        DataSource pool = new MyPool();
        ResultSet rs = null;
        try {
            conn = pool.getConnection();
            String sql = "select * from user where name=?";
            pstate = conn.prepareStatement(sql);
            pstate.setString(1, "test");
            rs = pstate.executeQuery();
            while(rs.next()) {
                System.out.println(rs.getString("name"));
            }
        }catch(Exception e) {
            throw new RuntimeException(e);
        }finally {
            DBUtils.release(rs, pstate, conn);
        }
    }

}

工具类：

package cn.sasa.utils;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ResourceBundle;

public class DBUtils {
    private static Connection conn = null;
    private static String driver = null;
    private static String url = null;
    private static String user = null;
    private static String pwd = null;
    //注册驱动
    static {
        try {
            ResourceBundle bundle = ResourceBundle.getBundle("database");
            driver = bundle.getString("driver");
            url = bundle.getString("url");
            user = bundle.getString("user");
            pwd = bundle.getString("pwd");
            Class.forName(driver);
            conn = DriverManager.getConnection(url, user, pwd);
        }catch(Exception e) {
            throw new RuntimeException(e);
        }
    }
    
    //获取连接对象
    public static Connection getConnection() {
        return conn;
    }
    
    //销毁资源 查询
    public static void release(ResultSet rs, PreparedStatement state, Connection conn ) {
        if(rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if(state != null) {
            try {
                state.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if(conn!=null) {
            try {
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    //销毁资源 增删改
    public static void release(PreparedStatement state, Connection conn) {
        if(state != null) {
            try {
                state.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if(conn!=null) {
            try {
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

数据库配置文件略。