JDBC

一、数据库连接池

1.数据库连接池的概念

• 数据库连接背景
  • 数据库连接是一种关键的、有限的、昂贵的资源，这一点在多用户的网页应用程序中体现得尤为突出。对数据库连接的管理能显著影响到整个应用程序的伸缩性和健壮性，影响到程序的性能指标。数据库连接池正是针对这个问题提出来的。
• 数据库连接池
  • 数据库连接池负责分配、管理和释放数据库连接，它允许应用程序重复使用一个现有的数据库连接，而不是再重新建立一个。这项技术能明显提高对数据库操作的性能。
• 数据库连接池原理

2.自定义连接池

• java.sql.DataSource接口：数据源(数据库连接池)。java官方提供的数据库连接池规范(接口)
  • 获取数据库连接对象：Connection getConnection();
• 自定义连接池

/*
	自定义连接池类
*/
public class MyDataSource implements DataSource{
    //定义集合容器，用于保存多个数据库连接对象
    private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());

    //静态代码块，生成10个数据库连接保存到集合中
    static {
        for (int i = 0; i < 10; i++) {
            Connection con = JDBCUtils.getConnection();
            pool.add(con);
        }
    }

    //返回连接池的大小
    public int getSize() {
        return pool.size();
    }

    //从池中返回一个数据库连接
    @Override
    public Connection getConnection() {
        if(pool.size() > 0) {
            //从池中获取数据库连接
            return pool.remove(0);
        }else {
            throw new RuntimeException("连接数量已用尽");
        }
    }

    @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;
    }
}

3.自定义连接池测试

public class MyDataSourceTest {
    public static void main(String[] args) throws Exception{
        //创建数据库连接池对象
        MyDataSource dataSource = new MyDataSource();

        System.out.println("使用之前连接池数量：" + dataSource.getSize());
        
        //获取数据库连接对象
        Connection con = dataSource.getConnection();
        System.out.println(con.getClass());// JDBC4Connection

        //查询学生表全部信息
        String sql = "SELECT * FROM student";
        PreparedStatement pst = con.prepareStatement(sql);
        ResultSet rs = pst.executeQuery();

        while(rs.next()) {
            System.out.println(rs.getInt("sid") + "\t" + rs.getString("name") + "\t" + rs.getInt("age") + "\t" + rs.getDate("birthday"));
        }
        
        //释放资源
        rs.close();
        pst.close();
		//目前的连接对象close方法，是直接关闭连接，而不是将连接归还池中
        con.close();

        System.out.println("使用之后连接池数量：" + dataSource.getSize());
    }
}

4.归还连接

• 继承(无法解决)

  • 通过打印连接对象，发现DriverManager获取的连接实现类是JDBC4Connection。
  • 自定义一个类，继承JDBC4Connection这个类，重写close()方法。

  /*
      自定义Connection类
   */
  public class MyConnection1 extends JDBC4Connection {
      //声明连接对象和连接池集合对象
      private Connection con;
      private List<Connection> pool;
  
      //通过构造方法给成员变量赋值
      public MyConnection1(String hostToConnectTo, int portToConnectTo, Properties info, String databaseToConnectTo, String url,Connection con,List<Connection> pool) throws SQLException {
          super(hostToConnectTo, portToConnectTo, info, databaseToConnectTo, url);
          this.con = con;
          this.pool = pool;
      }
  
      //重写close()方法，将连接归还给池中
      @Override
      public void close() throws SQLException {
          pool.add(con);
      }
  }
  

  • 但是这种方式行不通，通过查看JDBC工具类获取连接的方法我们发现：我们虽然自定义了一个子类，完成了归还连接的操作。但是DriverManager获取的还是JDBC4Connection这个对象，并不是我们的子类对象。而我们又不能整体去修改驱动包中类的功能！

  //将之前的连接对象换成自定义的子类对象
  private static MyConnection1 con;
  
  //4.获取数据库连接的方法
  public static Connection getConnection() {
      try {
          //等效于：MyConnection1 con = new JDBC4Connection();  语法错误！
          con = DriverManager.getConnection(url,username,password);
      } catch (SQLException e) {
          e.printStackTrace();
      }
  
      return con;
  }
  

• 装饰设计模式

  • 自定义连接类

  /*
      自定义Connection类。通过装饰设计模式，实现和mysql驱动包中的Connection实现类相同的功能！
      实现步骤：
          1.定义一个类，实现Connection接口
          2.定义Connection连接对象和连接池容器对象的变量
          3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值
          4.在close()方法中，完成连接的归还
          5.剩余方法，只需要调用mysql驱动包的连接对象完成即可
   */
  public class MyConnection2 implements Connection {
  
      //2.定义Connection连接对象和连接池容器对象的变量
      private Connection con;
      private List<Connection> pool;
  
      //3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值
      public MyConnection2(Connection con,List<Connection> pool) {
          this.con = con;
          this.pool = pool;
      }
  
      //4.在close()方法中，完成连接的归还
      @Override
      public void close() throws SQLException {
          pool.add(con);
      }
  
  
      @Override
      public Statement createStatement() throws SQLException {
          return con.createStatement();
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql) throws SQLException {
          return con.prepareStatement(sql);
      }
  
      @Override
      public CallableStatement prepareCall(String sql) throws SQLException {
          return con.prepareCall(sql);
      }
  
      @Override
      public String nativeSQL(String sql) throws SQLException {
          return con.nativeSQL(sql);
      }
  
      @Override
      public void setAutoCommit(boolean autoCommit) throws SQLException {
          con.setAutoCommit(autoCommit);
      }
  
      @Override
      public boolean getAutoCommit() throws SQLException {
          return con.getAutoCommit();
      }
  
      @Override
      public void commit() throws SQLException {
          con.commit();
      }
  
      @Override
      public void rollback() throws SQLException {
          con.rollback();
      }
  
      @Override
      public boolean isClosed() throws SQLException {
          return con.isClosed();
      }
  
      @Override
      public DatabaseMetaData getMetaData() throws SQLException {
          return con.getMetaData();
      }
  
      @Override
      public void setReadOnly(boolean readOnly) throws SQLException {
          con.setReadOnly(readOnly);
      }
  
      @Override
      public boolean isReadOnly() throws SQLException {
          return con.isReadOnly();
      }
  
      @Override
      public void setCatalog(String catalog) throws SQLException {
          con.setCatalog(catalog);
      }
  
      @Override
      public String getCatalog() throws SQLException {
          return con.getCatalog();
      }
  
      @Override
      public void setTransactionIsolation(int level) throws SQLException {
          con.setTransactionIsolation(level);
      }
  
      @Override
      public int getTransactionIsolation() throws SQLException {
          return con.getTransactionIsolation();
      }
  
      @Override
      public SQLWarning getWarnings() throws SQLException {
          return con.getWarnings();
      }
  
      @Override
      public void clearWarnings() throws SQLException {
          con.clearWarnings();
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public Map<String, Class<?>> getTypeMap() throws SQLException {
          return con.getTypeMap();
      }
  
      @Override
      public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
          con.setTypeMap(map);
      }
  
      @Override
      public void setHoldability(int holdability) throws SQLException {
          con.setHoldability(holdability);
      }
  
      @Override
      public int getHoldability() throws SQLException {
          return con.getHoldability();
      }
  
      @Override
      public Savepoint setSavepoint() throws SQLException {
          return con.setSavepoint();
      }
  
      @Override
      public Savepoint setSavepoint(String name) throws SQLException {
          return con.setSavepoint(name);
      }
  
      @Override
      public void rollback(Savepoint savepoint) throws SQLException {
          con.rollback(savepoint);
      }
  
      @Override
      public void releaseSavepoint(Savepoint savepoint) throws SQLException {
          con.releaseSavepoint(savepoint);
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
          return con.prepareStatement(sql,autoGeneratedKeys);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
          return con.prepareStatement(sql,columnIndexes);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
          return con.prepareStatement(sql,columnNames);
      }
  
      @Override
      public Clob createClob() throws SQLException {
          return con.createClob();
      }
  
      @Override
      public Blob createBlob() throws SQLException {
          return con.createBlob();
      }
  
      @Override
      public NClob createNClob() throws SQLException {
          return con.createNClob();
      }
  
      @Override
      public SQLXML createSQLXML() throws SQLException {
          return con.createSQLXML();
      }
  
      @Override
      public boolean isValid(int timeout) throws SQLException {
          return con.isValid(timeout);
      }
  
      @Override
      public void setClientInfo(String name, String value) throws SQLClientInfoException {
          con.setClientInfo(name,value);
      }
  
      @Override
      public void setClientInfo(Properties properties) throws SQLClientInfoException {
          con.setClientInfo(properties);
      }
  
      @Override
      public String getClientInfo(String name) throws SQLException {
          return con.getClientInfo(name);
      }
  
      @Override
      public Properties getClientInfo() throws SQLException {
          return con.getClientInfo();
      }
  
      @Override
      public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
          return con.createArrayOf(typeName,elements);
      }
  
      @Override
      public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
          return con.createStruct(typeName,attributes);
      }
  
      @Override
      public void setSchema(String schema) throws SQLException {
          con.setSchema(schema);
      }
  
      @Override
      public String getSchema() throws SQLException {
          return con.getSchema();
      }
  
      @Override
      public void abort(Executor executor) throws SQLException {
          con.abort(executor);
      }
  
      @Override
      public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
          con.setNetworkTimeout(executor,milliseconds);
      }
  
      @Override
      public int getNetworkTimeout() throws SQLException {
          return con.getNetworkTimeout();
      }
  
      @Override
      public <T> T unwrap(Class<T> iface) throws SQLException {
          return con.unwrap(iface);
      }
  
      @Override
      public boolean isWrapperFor(Class<?> iface) throws SQLException {
          return con.isWrapperFor(iface);
      }
  }
  

  • 自定义连接池类

  public class MyDataSource implements DataSource{
      //定义集合容器，用于保存多个数据库连接对象
      private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());
  
      //静态代码块，生成10个数据库连接保存到集合中
      static {
          for (int i = 0; i < 10; i++) {
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
  
      //返回连接池的大小
      public int getSize() {
          return pool.size();
      }
  
      //从池中返回一个数据库连接
      @Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
              //通过自定义连接对象进行包装
              MyConnection2 mycon = new MyConnection2(con,pool);
              //返回包装后的连接对象
              return mycon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }
  }
  

• 适配器设计模式

  • 通过之前MyConnection2连接类我们发现，有很多个需要实现的方法。这个时候我们就可以使用适配器设计模式了。提供一个适配器类，实现Connection接口，将所有功能进行实现(除了close方法)。自定义连接类只需要继承这个适配器类，重写需要改进的close()方法即可！
  • 适配器类

  /*
      适配器抽象类。实现Connection接口。
      实现所有的方法，调用mysql驱动包中Connection连接对象的方法
   */
  public abstract class MyAdapter implements Connection {
  
      // 定义数据库连接对象的变量
      private Connection con;
  
      // 通过构造方法赋值
      public MyAdapter(Connection con) {
          this.con = con;
      }
  
      // 所有的方法，均调用mysql的连接对象实现
      @Override
      public Statement createStatement() throws SQLException {
          return con.createStatement();
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql) throws SQLException {
          return con.prepareStatement(sql);
      }
  
      @Override
      public CallableStatement prepareCall(String sql) throws SQLException {
          return con.prepareCall(sql);
      }
  
      @Override
      public String nativeSQL(String sql) throws SQLException {
          return con.nativeSQL(sql);
      }
  
      @Override
      public void setAutoCommit(boolean autoCommit) throws SQLException {
          con.setAutoCommit(autoCommit);
      }
  
      @Override
      public boolean getAutoCommit() throws SQLException {
          return con.getAutoCommit();
      }
  
      @Override
      public void commit() throws SQLException {
          con.commit();
      }
  
      @Override
      public void rollback() throws SQLException {
          con.rollback();
      }
  
      @Override
      public boolean isClosed() throws SQLException {
          return con.isClosed();
      }
  
      @Override
      public DatabaseMetaData getMetaData() throws SQLException {
          return con.getMetaData();
      }
  
      @Override
      public void setReadOnly(boolean readOnly) throws SQLException {
          con.setReadOnly(readOnly);
      }
  
      @Override
      public boolean isReadOnly() throws SQLException {
          return con.isReadOnly();
      }
  
      @Override
      public void setCatalog(String catalog) throws SQLException {
          con.setCatalog(catalog);
      }
  
      @Override
      public String getCatalog() throws SQLException {
          return con.getCatalog();
      }
  
      @Override
      public void setTransactionIsolation(int level) throws SQLException {
          con.setTransactionIsolation(level);
      }
  
      @Override
      public int getTransactionIsolation() throws SQLException {
          return con.getTransactionIsolation();
      }
  
      @Override
      public SQLWarning getWarnings() throws SQLException {
          return con.getWarnings();
      }
  
      @Override
      public void clearWarnings() throws SQLException {
          con.clearWarnings();
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public Map<String, Class<?>> getTypeMap() throws SQLException {
          return con.getTypeMap();
      }
  
      @Override
      public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
          con.setTypeMap(map);
      }
  
      @Override
      public void setHoldability(int holdability) throws SQLException {
          con.setHoldability(holdability);
      }
  
      @Override
      public int getHoldability() throws SQLException {
          return con.getHoldability();
      }
  
      @Override
      public Savepoint setSavepoint() throws SQLException {
          return con.setSavepoint();
      }
  
      @Override
      public Savepoint setSavepoint(String name) throws SQLException {
          return con.setSavepoint(name);
      }
  
      @Override
      public void rollback(Savepoint savepoint) throws SQLException {
          con.rollback(savepoint);
      }
  
      @Override
      public void releaseSavepoint(Savepoint savepoint) throws SQLException {
          con.releaseSavepoint(savepoint);
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
          return con.prepareStatement(sql,autoGeneratedKeys);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
          return con.prepareStatement(sql,columnIndexes);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
          return con.prepareStatement(sql,columnNames);
      }
  
      @Override
      public Clob createClob() throws SQLException {
          return con.createClob();
      }
  
      @Override
      public Blob createBlob() throws SQLException {
          return con.createBlob();
      }
  
      @Override
      public NClob createNClob() throws SQLException {
          return con.createNClob();
      }
  
      @Override
      public SQLXML createSQLXML() throws SQLException {
          return con.createSQLXML();
      }
  
      @Override
      public boolean isValid(int timeout) throws SQLException {
          return con.isValid(timeout);
      }
  
      @Override
      public void setClientInfo(String name, String value) throws SQLClientInfoException {
          con.setClientInfo(name,value);
      }
  
      @Override
      public void setClientInfo(Properties properties) throws SQLClientInfoException {
          con.setClientInfo(properties);
      }
  
      @Override
      public String getClientInfo(String name) throws SQLException {
          return con.getClientInfo(name);
      }
  
      @Override
      public Properties getClientInfo() throws SQLException {
          return con.getClientInfo();
      }
  
      @Override
      public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
          return con.createArrayOf(typeName,elements);
      }
  
      @Override
      public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
          return con.createStruct(typeName,attributes);
      }
  
      @Override
      public void setSchema(String schema) throws SQLException {
          con.setSchema(schema);
      }
  
      @Override
      public String getSchema() throws SQLException {
          return con.getSchema();
      }
  
      @Override
      public void abort(Executor executor) throws SQLException {
          con.abort(executor);
      }
  
      @Override
      public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
          con.setNetworkTimeout(executor,milliseconds);
      }
  
      @Override
      public int getNetworkTimeout() throws SQLException {
          return con.getNetworkTimeout();
      }
  
      @Override
      public <T> T unwrap(Class<T> iface) throws SQLException {
          return con.unwrap(iface);
      }
  
      @Override
      public boolean isWrapperFor(Class<?> iface) throws SQLException {
          return con.isWrapperFor(iface);
      }
  }
  

  • 自定义连接类

  /*
      自定义Connection连接类。通过适配器设计模式。完成close()方法的重写
          1.定义一个类，继承适配器父类
          2.定义Connection连接对象和连接池容器对象的变量
          3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值
          4.在close()方法中，完成连接的归还
   */
  public class MyConnection3 extends MyAdapter {
      //2.定义Connection连接对象和连接池容器对象的变量
      private Connection con;
      private List<Connection> pool;
  
      //3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值
      public MyConnection3(Connection con,List<Connection> pool) {
          super(con);    // 将接收的数据库连接对象给适配器父类传递
          this.con = con;
          this.pool = pool;
      }
  
      //4.在close()方法中，完成连接的归还
      @Override
      public void close() throws SQLException {
          pool.add(con);
      }
  }
  

  • 自定义连接池类

  public class MyDataSource implements DataSource{
      //定义集合容器，用于保存多个数据库连接对象
      private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());
  
      //静态代码块，生成10个数据库连接保存到集合中
      static {
          for (int i = 0; i < 10; i++) {
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
  
      //返回连接池的大小
      public int getSize() {
          return pool.size();
      }
  
      //从池中返回一个数据库连接
      @Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
  
              //通过自定义连接对象进行包装
              //MyConnection2 mycon = new MyConnection2(con,pool);
              MyConnection3 mycon = new MyConnection3(con,pool);
  
              //返回包装后的连接对象
              return mycon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }
  }
  
  

• 动态代理

  • 经过我们适配器模式的改进，自定义连接类中的方法已经很简洁了。剩余所有的方法已经抽取到了适配器类中。但是适配器这个类还是我们自己编写的，也比较麻烦！所以可以使用动态代理的方式来改进。
  • 自定义数据库连接池类

  public class MyDataSource implements DataSource{
      //定义集合容器，用于保存多个数据库连接对象
      private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());
  
      //静态代码块，生成10个数据库连接保存到集合中
      static {
          for (int i = 0; i < 10; i++) {
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
  
      //返回连接池的大小
      public int getSize() {
          return pool.size();
      }
  
      //动态代理方式
      @Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
  
              Connection proxyCon = (Connection)Proxy.newProxyInstance(con.getClass().getClassLoader(), new Class[]{Connection.class}, new InvocationHandler() {
                  /*
                      执行Connection实现类所有方法都会经过invoke
                      如果是close方法，则将连接还回池中
                      如果不是，直接执行实现类的原有方法
                   */
                  @Override
                  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                      if(method.getName().equals("close")) {
                          pool.add(con);
                          return null;
                      }else {
                          return method.invoke(con,args);
                      }
                  }
              });
  
              return proxyCon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }
  
  
      //从池中返回一个数据库连接
      /*@Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
  
              //通过自定义连接对象进行包装
              //MyConnection2 mycon = new MyConnection2(con,pool);
              MyConnection3 mycon = new MyConnection3(con,pool);
  
              //返回包装后的连接对象
              return mycon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }*/
  }
  
  

5.开源连接池的使用

• C3P0

  • 基本使用

  /*
      使用C3P0连接池
      1.导入jar包
      2.导入配置文件到src目录下
      3.创建c3p0连接池对象
      4.获取数据库连接进行使用
   */
  public class C3P0Demo1 {
      public static void main(String[] args) throws Exception{
          //创建c3p0连接池对象
          DataSource dataSource = new ComboPooledDataSource();
  
          //获取数据库连接进行使用
          Connection con = dataSource.getConnection();
  
          //查询全部学生信息
          String sql = "SELECT * FROM student";
          PreparedStatement pst = con.prepareStatement(sql);
          ResultSet rs = pst.executeQuery();
  
          while(rs.next()) {
              System.out.println(rs.getInt("sid") + "\t" + rs.getString("name") + "\t" + rs.getInt("age") + "\t" + rs.getDate("birthday"));
          }
  
          //释放资源
          rs.close();
          pst.close();
          con.close();    // 将连接对象归还池中
      }
  }
  
  

  • 配置演示

  public class C3P0Demo2 {
      public static void main(String[] args) throws Exception{
          //创建c3p0连接池对象
          DataSource dataSource = new ComboPooledDataSource();
  
          //获取数据库连接进行使用
          for(int i = 1; i <= 11; i++) {
              Connection con = dataSource.getConnection();
              System.out.println(i + ":" + con);
              if(i == 5) {
                  con.close();
              }
          }
      }
  }
  
  

• Druid

  • 基本使用

  /*
      Druid连接池
      1.导入jar包
      2.编写配置文件，放在src目录下
      3.通过Properties集合加载配置文件
      4.通过Druid连接池工厂类获取数据库连接池对象
      5.获取数据库连接，进行使用
   */
  public class DruidDemo1 {
      public static void main(String[] args) throws Exception{
          //通过Properties集合加载配置文件
          InputStream is = DruidDemo1.class.getClassLoader().getResourceAsStream("druid.properties");
          Properties prop = new Properties();
          prop.load(is);
  
          //通过Druid连接池工厂类获取数据库连接池对象
          DataSource dataSource = DruidDataSourceFactory.createDataSource(prop);
  
          //获取数据库连接，进行使用
          Connection con = dataSource.getConnection();
  
          //查询全部学生信息
          String sql = "SELECT * FROM student";
          PreparedStatement pst = con.prepareStatement(sql);
          ResultSet rs = pst.executeQuery();
  
          while(rs.next()) {
              System.out.println(rs.getInt("sid") + "\t" + rs.getString("name") + "\t" + rs.getInt("age") + "\t" + rs.getDate("birthday"));
          }
  
          //释放资源
          rs.close();
          pst.close();
          con.close();    // 将连接对象归还池中
      }
  }
  
  

  • 抽取工具类

  /*
      数据库连接池工具类
   */
  public class DataSourceUtils {
      //1.私有构造方法
      private DataSourceUtils(){}
  
      //2.定义DataSource数据源变量
      private static DataSource dataSource;
  
      //3.提供静态代码块，完成配置文件的加载和获取连接池对象
      static {
          try{
              //加载配置文件
              InputStream is = DruidDemo1.class.getClassLoader().getResourceAsStream("druid.properties");
              Properties prop = new Properties();
              prop.load(is);
  
              //获取数据库连接池对象
              dataSource = DruidDataSourceFactory.createDataSource(prop);
  
          } catch(Exception e) {
              e.printStackTrace();
          }
      }
  
      //4.提供获取数据库连接的方法
      public static Connection getConnection() {
          Connection con = null;
          try {
              con = dataSource.getConnection();
          } catch (SQLException e) {
              e.printStackTrace();
          }
          return con;
      }
  
      //5.提供获取数据库连接池的方法
      public static DataSource getDataSource() {
          return dataSource;
      }
  
      //6.提供释放资源的方法
      public static void close(Connection con, Statement stat, ResultSet rs) {
          if(con != null) {
              try {
                  con.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
  
          if(stat != null) {
              try {
                  stat.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
  
          if(rs != null) {
              try {
                  rs.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
      }
  
      public static void close(Connection con, Statement stat) {
          close(con,stat,null);
      }
  
  }
  
  

二、JDBC框架(JDBCTemplate)

1.分析案例中的重复代码

• dao层的重复代码
  • 定义必要的信息、获取数据库的连接、释放资源都是重复的代码！
  • 而我们最终的核心功能仅仅只是执行一条sql语句而已啊！
  • 所以我们可以抽取出一个JDBC模板类，来封装一些方法(update、query)，专门帮我们执行增删改查的sql语句！
  • 将之前那些重复的操作，都抽取到模板类中的方法里。就能大大简化我们的使用步骤！

2.自定义JDBC框架

2.1数据库的源信息

• DataBaseMetaData(了解)：数据库的源信息
  • java.sql.DataBaseMetaData：封装了整个数据库的综合信息
  • 例如：
    • String getDatabaseProductName()：获取数据库产品的名称
    • int getDatabaseProductVersion()：获取数据库产品的版本号
• ParameterMetaData：参数的源信息
  • java.sql.ParameterMetaData：封装的是预编译执行者对象中每个参数的类型和属性
  • 这个对象可以通过预编译执行者对象中的getParameterMetaData()方法来获取
  • 核心功能：
    • int getParameterCount()：获取sql语句中参数的个数
• ResultSetMetaData：结果集的源信息
  • java.sql.ResultSetMetaData：封装的是结果集对象中列的类型和属性
  • 这个对象可以通过结果集对象中的getMetaData()方法来获取
  • 核心功能：
    • int getColumnCount()：获取列的总数
    • String getColumnName(int i)：获取列名

2.2JDBCTemplate类增删改功能的编写

public class JDBCTemplate {
    private DataSource dataSource;
    private Connection con;
    private PreparedStatement pst;
    private ResultSet rs;

    public JDBCTemplate(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    //专用于执行增删改sql语句的方法
    public int update(String sql,Object...objs) {
        int result = 0;

        try{
            con = dataSource.getConnection();
            pst = con.prepareStatement(sql);

            //获取sql语句中的参数源信息
            ParameterMetaData pData = pst.getParameterMetaData();
            //获取sql语句中参数的个数
            int parameterCount = pData.getParameterCount();

            //判断参数个数是否一致
            if(parameterCount != objs.length) {
                throw new RuntimeException("参数个数不匹配");
            }

            //为sql语句中的?占位符赋值
            for (int i = 0; i < objs.length; i++) {
                pst.setObject(i+1,objs[i]);
            }

            //执行sql语句
            result = pst.executeUpdate();

        } catch(Exception e) {
            e.printStackTrace();
        } finally {
            //释放资源
            DataSourceUtils.close(con,pst);
        }

        //返回结果
        return result;
    }
}

2.3JDBCTemplate类查询功能的编写

• 实体类

/*
    学生实体类
 */
public class Student {
    private Integer sid;
    private String name;
    private Integer age;
    private Date birthday;

    public Student() {
    }

    public Student(Integer sid, String name, Integer age, Date birthday) {
        this.sid = sid;
        this.name = name;
        this.age = age;
        this.birthday = birthday;
    }

    public Integer getSid() {
        return sid;
    }

    public void setSid(Integer sid) {
        this.sid = sid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    @Override
    public String toString() {
        return "Student{" +
                "sid=" + sid +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", birthday=" + birthday +
                '}';
    }
}

• ResultSetHandler接口

/*
    用于处理结果集的接口
 */
public interface ResultSetHandler<T> {
    //处理结果集的抽象方法。
    <T> T handler(ResultSet rs);
}

• BeanHandler实现类

/*
    实现类1：用于完成将查询出来的一条记录，封装到Student对象中
 */
public class BeanHandler<T> implements ResultSetHandler<T> {
    //1.声明对象类型变量
    private Class<T> beanClass;

    //2.有参构造对变量赋值
    public BeanHandler(Class<T> beanClass) {
        this.beanClass = beanClass;
    }

    /*
        将ResultSet结果集中的数据封装到beanClass类型对象中
     */
    @Override
    public T handler(ResultSet rs) {
        //3.声明对象
        T bean = null;
        try{
            //4.创建传递参数的对象
            bean = beanClass.newInstance();

            //5.判断是否有结果集
            if(rs.next()) {
                //6.得到所有的列名
                //6.1先得到结果集的源信息
                ResultSetMetaData rsmd = rs.getMetaData();
                //6.2还要得到有多少列
                int columnCount = rsmd.getColumnCount();
                //6.3遍历列数
                for(int i = 1; i <= columnCount; i++) {
                    //6.4得到每列的列名
                    String columnName = rsmd.getColumnName(i);
                    //6.5通过列名获取数据
                    Object columnValue = rs.getObject(columnName);

                    //6.6列名其实就是对象中成员变量的名称。于是就可以使用列名得到对象中属性的描述器(get和set方法)
                    PropertyDescriptor pd = new PropertyDescriptor(columnName.toLowerCase(),beanClass);
                    //6.7获取set方法
                    Method writeMethod = pd.getWriteMethod();
                    //6.8执行set方法，给成员变量赋值
                    writeMethod.invoke(bean,columnValue);
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        //7.将对象返回
        return bean;
    }
}

• BeanListHandler实现类

/*
    实现类2：用于将结果集封装到集合中
 */
public class BeanListHandler<T> implements ResultSetHandler<T> {

    //1.声明对象变量
    private Class<T> beanClass;

    //2.有参构造为变量赋值
    public BeanListHandler(Class<T> beanClass) {
        this.beanClass = beanClass;
    }

    @Override
    public List<T> handler(ResultSet rs) {
        //3.创建集合对象
        List<T> list = new ArrayList<>();

        try{
            //4.遍历结果集对象
            while(rs.next()) {
                //5.创建传递参数的对象
                T bean = beanClass.newInstance();
                //6.得到所有的列名
                //6.1先得到结果集的源信息
                ResultSetMetaData rsmd = rs.getMetaData();
                //6.2还要得到有多少列
                int columnCount = rsmd.getColumnCount();
                //6.3遍历列数
                for(int i = 1; i <= columnCount; i++) {
                    //6.4得到每列的列名
                    String columnName = rsmd.getColumnName(i);
                    //6.5通过列名获取数据
                    Object columnValue = rs.getObject(columnName);

                    //6.6列名其实就是对象中成员变量的名称。于是就可以使用列名得到对象中属性的描述器(get和set方法)
                    PropertyDescriptor pd = new PropertyDescriptor(columnName.toLowerCase(),beanClass);
                    //6.7获取set方法
                    Method writeMethod = pd.getWriteMethod();
                    //6.8执行set方法，给成员变量赋值
                    writeMethod.invoke(bean,columnValue);
                }
                //7.将对象保存到集合中
                list.add(bean);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        //8.返回结果
        return list;
    }
}

• ScalarHandler实现类

/*
    实现类3：用于返回一个聚合函数的查询结果
 */
public class ScalarHandler<T> implements ResultSetHandler<T> {
    @Override
    public Long handler(ResultSet rs) {
        //1.声明一个变量
        Long value = null;
        try{
            //2.判断是否有结果
            if(rs.next()) {
                //3.获取结果集的源信息
                ResultSetMetaData rsmd = rs.getMetaData();
                //4.获取第一列的列名
                String columnName = rsmd.getColumnName(1);
                //5.根据列名获取值
                value = rs.getLong(columnName);
            }
        } catch(Exception e) {
            e.printStackTrace();
        }
        //6.将结果返回
        return value;
    }
}

• JDBCTemplate类

public class JDBCTemplate {
    private DataSource dataSource;
    private Connection con;
    private PreparedStatement pst;
    private ResultSet rs;

    public JDBCTemplate(DataSource dataSource) {
        this.dataSource = dataSource;
    }
    
    /*
    	专用于执行聚合函数sql语句的方法
    */
    public Long queryForScalar(String sql, ResultSetHandler<Long> rsh, Object...objs) {
        Long result = null;
        try{
            con = dataSource.getConnection();
            pst = con.prepareStatement(sql);

            //获取sql语句中的参数源信息
            ParameterMetaData pData = pst.getParameterMetaData();
            int parameterCount = pData.getParameterCount();

            //判断参数个数是否一致
            if(parameterCount != objs.length) {
                throw new RuntimeException("参数个数不匹配");
            }

            //为sql语句中的?占位符赋值
            for (int i = 0; i < objs.length; i++) {
                pst.setObject(i+1,objs[i]);
            }

            //执行sql语句
            rs = pst.executeQuery();

            //通过ScalarHandler方式对结果进行处理
            result = rsh.handler(rs);

        } catch(Exception e) {
            e.printStackTrace();
        } finally {
            //释放资源
            DataSourceUtils.close(con,pst,rs);
        }

        //将结果返回
        return result;
    }

    /*
    	专用于查询所有记录sql语句的方法
    */
    public <T> List<T> queryForList(String sql, ResultSetHandler<T> rsh, Object...objs) {
        List<T> list = new ArrayList<>();
        try{
            con = dataSource.getConnection();
            pst = con.prepareStatement(sql);

            //获取sql语句中的参数源信息
            ParameterMetaData pData = pst.getParameterMetaData();
            int parameterCount = pData.getParameterCount();

            //判断参数个数是否一致
            if(parameterCount != objs.length) {
                throw new RuntimeException("参数个数不匹配");
            }

            //为sql语句中的?占位符赋值
            for (int i = 0; i < objs.length; i++) {
                pst.setObject(i+1,objs[i]);
            }

            //执行sql语句
            rs = pst.executeQuery();

            //通过BeanListHandler方式对结果进行处理
            list = rsh.handler(rs);

        } catch(Exception e) {
            e.printStackTrace();
        } finally {
            //释放资源
            DataSourceUtils.close(con,pst,rs);
        }

        //将结果返回
        return list;
    }


    /*
    	专用于执行查询一条记录sql语句的方法
    */
    public <T> T queryForObject(String sql, ResultSetHandler<T> rsh, Object...objs) {
        T obj = null;
        try{
            con = dataSource.getConnection();
            pst = con.prepareStatement(sql);

            //获取sql语句中的参数源信息
            ParameterMetaData pData = pst.getParameterMetaData();
            int parameterCount = pData.getParameterCount();

            //判断参数个数是否一致
            if(parameterCount != objs.length) {
                throw new RuntimeException("参数个数不匹配");
            }

            //为sql语句中的?占位符赋值
            for (int i = 0; i < objs.length; i++) {
                pst.setObject(i+1,objs[i]);
            }

            //执行sql语句
            rs = pst.executeQuery();

            //通过BeanHandler方式对结果进行处理
            obj = rsh.handler(rs);

        } catch(Exception e) {
            e.printStackTrace();
        } finally {
            //释放资源
            DataSourceUtils.close(con,pst,rs);
        }

        //将结果返回
        return obj;
    }
}

2.4测试自定义JDBC框架的使用

public class JDBCTemplateTest {
    //创建JDBCTemplate对象
    JDBCTemplate template = new JDBCTemplate(DataSourceUtils.getDataSource());

    @Test
    public void selectScalar() {
        //查询student表的记录条数
        String sql = "SELECT COUNT(*) FROM student";
        Long count = template.queryForScalar(sql, new ScalarHandler<Long>());
        System.out.println(count);
    }

    @Test
    public void selectAll() {
        //查询所有学生信息
        String sql = "SELECT * FROM student";
        List<Student> list = template.queryForList(sql, new BeanListHandler<Student>(Student.class));
        for(Student stu : list) {
            System.out.println(stu);
        }
    }

    @Test
    public void selectOne() {
        //查询张三这条记录
        String sql = "SELECT * FROM student WHERE sid=?";
        //通过BeanHandler将结果封装成一个Student对象
        Student stu = template.queryForObject(sql, new BeanHandler<Student>(Student.class), 1);
        System.out.println(stu);
    }

    @Test
    public void insert() {
        //新增周七记录
        String sql = "INSERT INTO student VALUES (?,?,?,?)";
        Object[] params = {5,"周七",27,"2007-07-07"};
        int result = template.update(sql, params);
        System.out.println(result);
    }

    @Test
    public void delete() {
        //删除周七这条记录
        String sql = "DELETE FROM student WHERE sid=?";
        int result = template.update(sql, 5);
        System.out.println(result);
    }

    @Test
    public void update() {
        //修改张三的年龄为33
        String sql = "UPDATE student SET age=? WHERE name=?";
        Object[] params = {33,"张三"};
        int result = template.update(sql,params);
        System.out.println(result);
    }
}

emplate(DataSourceUtils.getDataSource());

@Test
public void selectScalar() {
    //查询student表的记录条数
    String sql = "SELECT COUNT(*) FROM student";
    Long count = template.queryForScalar(sql, new ScalarHandler<Long>());
    System.out.println(count);
}

@Test
public void selectAll() {
    //查询所有学生信息
    String sql = "SELECT * FROM student";
    List<Student> list = template.queryForList(sql, new BeanListHandler<Student>(Student.class));
    for(Student stu : list) {
        System.out.println(stu);
    }
}

@Test
public void selectOne() {
    //查询张三这条记录
    String sql = "SELECT * FROM student WHERE sid=?";
    //通过BeanHandler将结果封装成一个Student对象
    Student stu = template.queryForObject(sql, new BeanHandler<Student>(Student.class), 1);
    System.out.println(stu);
}

@Test
public void insert() {
    //新增周七记录
    String sql = "INSERT INTO student VALUES (?,?,?,?)";
    Object[] params = {5,"周七",27,"2007-07-07"};
    int result = template.update(sql, params);
    System.out.println(result);
}

@Test
public void delete() {
    //删除周七这条记录
    String sql = "DELETE FROM student WHERE sid=?";
    int result = template.update(sql, 5);
    System.out.println(result);
}

@Test
public void update() {
    //修改张三的年龄为33
    String sql = "UPDATE student SET age=? WHERE name=?";
    Object[] params = {33,"张三"};
    int result = template.update(sql,params);
    System.out.println(result);
}

}