学步园

DataSource用来取代DriverManager来获取Connection；

通过DataSource获得Connection速度很快；

通过DataSource获得的Connection都是已经被包裹过的（不是驱动原来的连接），他的close方法已经被修改。

一般DataSource内部会用一个连接池来缓存Connection，这样可以大幅度提高数据库的访问速度；

连接池可以理解成一个能够存放Connection的Collection；

我们的程序只和DataSource打交道，不会直接访问连接池；

 

使用装饰模式的Connection(核心代码)

class MyConnection implements Connection{

private Connection realConn;

private LinkedList connPool;

MyConnection(Connection rConn, LinkedList cPool){

this.realConn=rConn;

this.connPool=cPool;

}

public void close(){

this.connPool.addLast(this);

}

//….

}

  

class MyDataSource implements DataSource{

private LinkedList connPool = new Vector();

public Connection getConneciton (){

if(this.connPool.size()>0)

return this.connPool.removeFirst(0);

return createConnection();

}

private Connection createConnection(){

  Connection realConn = DriverManager.getConnection();

  Connection myConn =

new MyConnection(realConn,this.connPool);

  return myConn;

}

  

//….

}

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public class MyDataSource2 {
 private static String url = "jdbc:mysql://localhost:3306/jdbc";
 private static String user = "root";
 private static String password = "064417";
 private static int initCount = 3;
 private static int maxCount = 5;
 private int currentCount = 0;
 LinkedList<Connection> connectionsPool = new LinkedList<Connection>();
 public MyDataSource2() {
  for (int i = 0; i < initCount; i++) {
   try {
    this.connectionsPool.addLast(this.createConnection());
   } catch (SQLException e) {
    throw new ExceptionInInitializerError(e);
   }
  }
 }
 public Connection getConnection() throws SQLException {
  synchronized (connectionsPool) {
   if (this.connectionsPool.size() > 0) {
    return this.connectionsPool.removeFirst();
   } else if (this.currentCount < maxCount) {
    return this.createConnection();
   } else {
    throw new SQLException("已没链接");
   }
  }
 }
 public void free(Connection conn) {
   this.connectionsPool.addLast(conn);
 }
 private Connection createConnection() throws SQLException {
  this.currentCount++;
  Connection realconn=DriverManager.getConnection(url, user, password);
 //  MyConnection myConnection=new MyConnection(realconn,this);
//  return myConnection;
  MyConnectionHandler proxy= new MyConnectionHandler(this);
  return proxy.bind(realconn); }
}

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public class MyConnection implements Connection{
 public Connection realConnection;
 private MyDataSource2 dataSource;
 MyConnection(Connection connection,MyDataSource2 dataSource){
  this.realConnection=connection;
  this.dataSource=dataSource;
 }
 @Override
 public <T> T unwrap(Class<T> iface) throws SQLException {
  return this.realConnection.unwrap(iface);
 }
 @Override
 public boolean isWrapperFor(Class<?> iface) throws SQLException {
  return this.realConnection.isWrapperFor(iface);
 }
 @Override
 public Statement createStatement() throws SQLException {
  return this.realConnection.createStatement();
 }
 @Override
 public PreparedStatement prepareStatement(String sql) throws SQLException {
  return this.realConnection.prepareStatement(sql);
 }
 @Override
 public CallableStatement prepareCall(String sql) throws SQLException {
  return this.realConnection.prepareCall(sql);
 }
 @Override
 public String nativeSQL(String sql) throws SQLException {
  return this.realConnection.nativeSQL(sql);
 }
 @Override
 public void setAutoCommit(boolean autoCommit) throws SQLException {
  this.realConnection.setAutoCommit(autoCommit);
 }
 @Override
 public boolean getAutoCommit() throws SQLException {
  return this.realConnection.getAutoCommit();
 }
 @Override
 public void commit() throws SQLException {
  this.realConnection.commit();
 }
 @Override
 public void rollback() throws SQLException {
  this.realConnection.rollback();
 }
 @Override
 public void close() throws SQLException {
  this.dataSource.connectionsPool.addLast(this);
 }
 @Override
 public boolean isClosed() throws SQLException {
  return this.realConnection.isClosed();
 }
 @Override
 public DatabaseMetaData getMetaData() throws SQLException {
  return this.realConnection.getMetaData();
 }
 @Override
 public void setReadOnly(boolean readOnly) throws SQLException {
  this.realConnection.setReadOnly(readOnly);
 }
 @Override
 public boolean isReadOnly() throws SQLException {
  return this.realConnection.isReadOnly();
 }
 @Override
 public void setCatalog(String catalog) throws SQLException {
  this.realConnection.setCatalog(catalog);
 }
 @Override
 public String getCatalog() throws SQLException {
  return this.realConnection.getCatalog();
 }
 @Override
 public void setTransactionIsolation(int level) throws SQLException {
  this.realConnection.setTransactionIsolation(level);  
 }
 @Override
 public int getTransactionIsolation() throws SQLException {
  return this.realConnection.getTransactionIsolation();
 }
 @Override
 public SQLWarning getWarnings() throws SQLException {
  return this.realConnection.getWarnings();
 }
 @Override
 public void clearWarnings() throws SQLException {
  this.realConnection.clearWarnings();
 }
 @Override
 public Statement createStatement(int resultSetType, int resultSetConcurrency)
   throws SQLException {
  return this.realConnection.createStatement(resultSetType, resultSetConcurrency);
 }
 @Override
 public PreparedStatement prepareStatement(String sql, int resultSetType,
   int resultSetConcurrency) throws SQLException {
  return this.realConnection.prepareStatement(sql, resultSetType, resultSetConcurrency);
 }
 @Override
 public CallableStatement prepareCall(String sql, int resultSetType,
   int resultSetConcurrency) throws SQLException {
  return this.realConnection.prepareCall(sql, resultSetType, resultSetConcurrency);
 }
 @Override
 public Map<String, Class<?>> getTypeMap() throws SQLException {
  return this.realConnection.getTypeMap();
 }
 @Override
 public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
  this.realConnection.setTypeMap(map);  
 }
 @Override
 public void setHoldability(int holdability) throws SQLException {
  this.realConnection.setHoldability(holdability);  
 }
 @Override
 public int getHoldability() throws SQLException {
  return this.realConnection.getHoldability();
 }
 @Override
 public Savepoint setSavepoint() throws SQLException {
  return this.realConnection.setSavepoint();
 }
 @Override
 public Savepoint setSavepoint(String name) throws SQLException {
  return this.realConnection.setSavepoint(name);
 }
 @Override
 public void rollback(Savepoint savepoint) throws SQLException {
  this.realConnection.rollback(savepoint);  
 }
 @Override
 public void releaseSavepoint(Savepoint savepoint) throws SQLException {
  this.realConnection.releaseSavepoint(savepoint);  
 }
 @Override
 public Statement createStatement(int resultSetType,
   int resultSetConcurrency, int resultSetHoldability)
   throws SQLException {
  return this.realConnection.createStatement(resultSetType, resultSetConcurrency, resultSetHoldability);
 }
 @Override
 public PreparedStatement prepareStatement(String sql, int resultSetType,
   int resultSetConcurrency, int resultSetHoldability)
   throws SQLException {
  return this.realConnection.prepareStatement(sql, resultSetType, resultSetConcurrency, resultSetHoldability);
 }
 @Override
 public CallableStatement prepareCall(String sql, int resultSetType,
   int resultSetConcurrency, int resultSetHoldability)
   throws SQLException {
  return this.realConnection.prepareCall(sql, resultSetType, resultSetConcurrency, resultSetHoldability);
 }
 @Override
 public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys)
   throws SQLException {
  return this.realConnection.prepareStatement(sql, autoGeneratedKeys);
 }
 @Override
 public PreparedStatement prepareStatement(String sql, int[] columnIndexes)
   throws SQLException {
  return this.realConnection.prepareStatement(sql, columnIndexes);
 }
 @Override
 public PreparedStatement prepareStatement(String sql, String[] columnNames)
   throws SQLException {
  return this.realConnection.prepareStatement(sql, columnNames);
 }
 @Override
 public Clob createClob() throws SQLException {
  return this.realConnection.createClob();
 }
 @Override
 public Blob createBlob() throws SQLException {
  return this.realConnection.createBlob();
 }
 @Override
 public NClob createNClob() throws SQLException {
  return this.realConnection.createNClob();
 }
 @Override
 public SQLXML createSQLXML() throws SQLException {
  return this.realConnection.createSQLXML();
 }
 @Override
 public boolean isValid(int timeout) throws SQLException {
  return this.realConnection.isValid(timeout);
 }
 @Override
 public void setClientInfo(String name, String value)
   throws SQLClientInfoException {
  this.realConnection.setClientInfo(name, value); 
 }
 @Override
 public void setClientInfo(Properties properties)
   throws SQLClientInfoException {
  this.realConnection.setClientInfo(properties);
 }
 @Override
 public String getClientInfo(String name) throws SQLException {
  return this.realConnection.getClientInfo(name);
 }
 @Override
 public Properties getClientInfo() throws SQLException {
  return this.realConnection.getClientInfo();
 }
 @Override
 public Array createArrayOf(String typeName, Object[] elements)
   throws SQLException {
  return this.realConnection.createArrayOf(typeName, elements);
 }
 @Override
 public Struct createStruct(String typeName, Object[] attributes)
   throws SQLException {
  return this.realConnection.createStruct(typeName, attributes) ;
 }
 @Override
 public void setSchema(String schema) throws SQLException {
  this.setSchema(schema);
 }
 @Override
 public String getSchema() throws SQLException {
  return this.realConnection.getSchema();
 }
 @Override
 public void abort(Executor executor) throws SQLException {
  this.realConnection.abort(executor);
 }
 @Override
 public void setNetworkTimeout(Executor executor, int milliseconds)
   throws SQLException {
  this.realConnection.setNetworkTimeout(executor, milliseconds);
 }
 @Override
 public int getNetworkTimeout() throws SQLException {
  return this.realConnection.getNetworkTimeout();
 }
}

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public final class JdbcUtils {
// private static String url = "jdbc:mysql://localhost:3306/jdbc";
// private static String user = "root";
// private static String password = "064417";
 private static MyDataSource2 myDataSource = null;
 private JdbcUtils() {}
 static {
  try {
   // 注册驱动
   Class.forName("com.mysql.jdbc.Driver");// 推荐
   // DriverManager.registerDriver(new com.mysql.jdbc.Driver());//2
   // System.setProperty("jdbc.drivers",
   // "com.mysql.jdbc.Driver[:...:...]");//注册方式3可以注册多个驱动用“：”分隔。
   myDataSource = new MyDataSource2();
  } catch (ClassNotFoundException e) {
   throw new ExceptionInInitializerError(e);
  }
 }
 public static Connection getConnection() throws SQLException {
  // return DriverManager.getConnection(url, user, password);
  return myDataSource.getConnection();
 }
 public static void free(ResultSet rs, Statement st, Connection conn) {
  try {
   if (rs != null)
    rs.close();
  } catch (SQLException e) {
   e.printStackTrace();
  } finally {
   try {
    if (st != null)
     st.close();
   } catch (SQLException e) {
    e.printStackTrace();
   } finally {
    try {
     if (conn != null)
       conn.close();
//      myDataSource.free(conn);
    } catch (Exception e) {
     e.printStackTrace();
    }
   }
  }
 }
}

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public class Base {
 public static void main(String[] args) throws SQLException {
//  template();
  for(int i=0;i<10;i++){
   Connection conn=JdbcUtils.getConnection();
   System.out.println(conn);
   JdbcUtils.free(null, null, conn);
  }
 }

}

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public class MyConnectionHandler implements InvocationHandler {
 private Connection realConnection;
 private Connection warpedConnection;
 private MyDataSource2 dataSource;
 private int maxUseCount=5;
 private int currentUserCount=0;
 MyConnectionHandler(MyDataSource2 dataSource) {
  this.dataSource=dataSource;
 }
 Connection bind(Connection realconn) {
  this.realConnection=realconn;
//  newProxyInstance()在内存中动态产生一个新的类。第二个参数为所要实现的接口，
  warpedConnection = (Connection) Proxy.newProxyInstance(this
    .getClass().getClassLoader(), new Class[] { Connection.class },
    this);
  return warpedConnection;
 }
 @Override//调用处理器
 public Object invoke(Object proxy, Method method, Object[] args)
   throws Throwable {
  if("close".equals(method.getName())){
   this.currentUserCount++;
   if(this.currentUserCount<this.maxUseCount)
    this.dataSource.connectionsPool.addLast(this.warpedConnection);
   else{
    this.realConnection.close();
    this.currentUserCount--;
   }
  }
  return method.invoke(this.realConnection, args);
 }
}