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);
}
}