【愚公系列】2023年03月 Java教学课程 113-JDBC的（数据库连接池）

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一、数据库连接池

1.数据库连接池的概念

数据库连接池是一种用于管理数据库连接的技术，它可以在应用程序启动时创建一定数量的数据库连接，然后将这些连接放入一个连接池中，当应用程序需要访问数据库时，就从连接池中获取一个连接，并在使用完毕后将连接归还给连接池。这样可以避免频繁地创建和销毁数据库连接，从而提高数据库访问效率和性能。数据库连接池通常包含以下属性：最小连接数、最大连接数、连接超时时间、空闲连接回收时间等。

数据库连接池原理图

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

package com.itheima.utils;

import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

/*
    JDBC工具类
 */
public class JDBCUtils {
    
    
    //1.私有构造方法
    private JDBCUtils(){
    
    };

    //2.声明配置信息变量
    private static String driverClass;
    private static String url;
    private static String username;
    private static String password;
    private static Connection con;

    //3.静态代码块中实现加载配置文件和注册驱动
    static{
    
    
        try{
    
    
            //通过类加载器返回配置文件的字节流
            InputStream is = JDBCUtils.class.getClassLoader().getResourceAsStream("config.properties");

            //创建Properties集合，加载流对象的信息
            Properties prop = new Properties();
            prop.load(is);

            //获取信息为变量赋值
            driverClass = prop.getProperty("driverClass");
            url = prop.getProperty("url");
            username = prop.getProperty("username");
            password = prop.getProperty("password");

            //注册驱动
            Class.forName(driverClass);

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

    //4.获取数据库连接的方法
    public static Connection getConnection() {
    
    
        try {
    
    
            con = DriverManager.getConnection(url,username,password);
        } catch (SQLException e) {
    
    
            e.printStackTrace();
        }

        return con;
    }

    //5.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);
    }
}

package itheima01;

import com.itheima.utils.JDBCUtils;

import javax.sql.DataSource;
import java.io.PrintWriter;
import java.sql.*;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.logging.Logger;

/*
	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

package itheima01;

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

public class MyDataSourceTest {
    
    
    public static void main(String[] args) throws Exception{
    
    
        //1.创建连接池对象
        MyDataSource dataSource = new MyDataSource();

        System.out.println("使用之前的数量：" + dataSource.getSize());

        //2.通过连接池对象获取连接对象
        Connection con = dataSource.getConnection();
        System.out.println(con.getClass());

        //3.查询学生表的全部信息
        String sql = "SELECT * FROM student";
        PreparedStatement pst = con.prepareStatement(sql);

        //4.执行sql语句，接收结果集
        ResultSet rs = pst.executeQuery();

        //5.处理结果集
        while(rs.next()) {
    
    
            System.out.println(rs.getInt("sid") + "\t" + rs.getString("name") + "\t" + rs.getInt("age") + "\t" + rs.getDate("birthday"));
        }

        //6.释放资源
        rs.close();
        pst.close();
        con.close();    // 用完以后，关闭连接

        System.out.println("使用之后的数量：" + 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

    <c3p0-config>
        <!-- 使用默认的配置读取连接池对象 -->
        <default-config>
            <!--  连接参数 -->
            <property name="jdbcUrl">jdbc:mysql://localhost:3306/db14</property>
            <property name="user">root</property>
            <property name="password">123456</property>
    
            <!-- 连接池参数 -->
            <!--初始化的连接数量-->
            <property name="initialPoolSize">5</property>
            <!--最大连接数量-->
            <property name="maxPoolSize">10</property>
            <!--超时时间-->
            <property name="checkoutTimeout">3000</property>
        </default-config>
    
        <named-config name="otherc3p0">
            <!--  连接参数 -->
            <property name="jdbcUrl">jdbc:mysql://localhost:3306/db15</property>
            <property name="user">root</property>
            <property name="password">123456</property>
    
            <!-- 连接池参数 -->
            <property name="initialPoolSize">5</property>
            <property name="maxPoolSize">8</property>
            <property name="checkoutTimeout">1000</property>
        </named-config>
    </c3p0-config>
    

    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

    driverClassName=com.mysql.cj.jdbc.Driver
    url=jdbc:mysql://localhost:3306/db14
    username=root
    password=123456
    
    initialSize=5
    
    maxActive=10
    
    maxWait=3000
    

    /*
        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);
        }
    
    }
    
    

    public class DruidTest2 {
            
            
        public static void main(String[] args) throws Exception{
            
            
            //1.通过连接池工具类获取一个数据库连接
            Connection con = DataSourceUtils.getConnection();
    
            String sql = "SELECT * FROM student";
            PreparedStatement pst = con.prepareStatement(sql);
    
            //2.执行sql语句，接收结果集
            ResultSet rs = pst.executeQuery();
    
            //3.处理结果集
            while(rs.next()) {
            
            
                System.out.println(rs.getInt("sid") + "\t" + rs.getString("name") + "\t" + rs.getInt("age") + "\t" + rs.getDate("birthday"));
            }
    
            //4.释放资源
            DataSourceUtils.close(con,pst,rs);
        }
    }