JDBC自定义连接池

开发中，"获得连接"和"释放资源"是非常消耗系统资源的，为了解决此类性能问题可以采用连接池技术来共享连接Connection。

1、概述

用池来管理Connection,这样可以重复使用Connection.这样我们就不用创建Connection,用池来管理Connection对象，当使用完Connection对象后，将Connection对象归还给池，这样后续还可以从池中获取Connection对象，可以重新再利用这个连接对象啦。

java为数据库连接池提供了公共接口：javax.sql.DataSource,各个厂商需要让自己的连接池实现这个接口。

常见的连接池：DBCP,C3P0

2、自定义连接池

编写自定义连接池

1、创建连接池并实现接口javax.sql.DataSource，并使用接口中的getConnection()方法

2、提供一个集合，用于存放连接，可以采用LinkedList

3、后面程序如果需要，可以调用实现类getConnection(),并从list中获取链接。为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

4、当用户用完连接后，将连接归还到连接池中

3、自定义连接池采用装饰者设计模式

public class ConnectionPool implements Connection {

    private Connection connection;
    private LinkedList<Connection> pool;

    public ConnectionPool(Connection connection, LinkedList<Connection> pool){
        this.connection=connection;
        this.pool=pool;
    }

    @Override
    public PreparedStatement prepareStatement(String sql) throws SQLException {
        return connection.prepareStatement(sql);
    }

    @Override
    public void close() throws SQLException {
        pool.add(connection);

    }
    @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;
    }

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

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

DataSourcePool

public class DataSourcePool implements DataSource {
    //1.创建1个容器用于存储Connection对象
    private static LinkedList<Connection> pool = new LinkedList<Connection>();

    //2.创建5个连接放到容器中去
    static{
        for (int i = 0; i < 5; i++) {
            Connection conn = JDBCUtils.getConnection();
            //放入池子中connection对象已经经过改造了
            ConnectionPool connectionPool = new ConnectionPool(conn, pool);
            pool.add(connectionPool);
        }
    }

    /**
     * 重写获取连接的方法
     */
    @Override
    public Connection getConnection() throws SQLException {
        Connection conn = null;
        //3.使用前先判断
        if(pool.size()==0){
            //4.池子里面没有，我们再创建一些
            for (int i = 0; i < 5; i++) {
                conn = JDBCUtils.getConnection();
                //放入池子中connection对象已经经过改造了
                ConnectionPool connectionPool = new ConnectionPool(conn, pool);
                pool.add(connectionPool);
            }
        }
        //5.从池子里面获取一个连接对象Connection
        conn = pool.remove(0);
        return conn;
    }

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

    @Override
    public Logger getParentLogger() throws SQLFeatureNotSupportedException {
        return null;
    }
}

测试代码如下

 @Test
    public void test1(){
        Connection conn = null;
        PreparedStatement pstmt = null;
        // 1.创建自定义连接池对象
        DataSource dataSource = new DataSourcePool();
        try {
            // 2.从池子中获取连接
            conn = dataSource.getConnection();
            String sql = "insert into USER values(?,?)";
            //3.必须在自定义的connection类中重写prepareStatement(sql)方法
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "李四");
            pstmt.setString(2, "1234");
            int rows = pstmt.executeUpdate();
            System.out.println("rows:"+rows);
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            JDBCUtils.relase(conn, pstmt, null);
        }
    }