连接池-归还连接详解(上)

• 目录

  归还数据库连接的方式

  继承方式归还数据库连接的思想

  继承方式归还数据库连接的实现步骤

  继承方式归还数据库连接存在的问题

  装饰设计模式归还数据库连接的思想

  装饰设计模式归还数据库连接的实现步骤

  装饰设计模式归还数据库连接存在的问题

  装饰设计模式归还实例演示

  ---

• 归还数据库连接的方式

• 继承方式
• 装饰设计模式
• 适配器设计模式
• 动态代理方式

• 继承方式归还数据库连接的思想

• 通过打印连接对象，发现DriverManager获取的连接实现类是JDBC4Connection
• 那我们就可以自定义一个类，继承JDBC4Connection这个类，重写close()方法，完成连接对象的归还

• 继承方式归还数据库连接的实现步骤

• 1.定义一个类，继承JDBC4Connection
• 2.定义Connection连接对象和连接池容器对象的成员变量
• 3.通过有参构造方法完成对成员变量的赋值
• 4.重写close方法，将连接对象添加到池中

• 继承方式归还数据库连接存在的问题

• 通过查看JDBC工具类获取连接的方法发现
• 我们虽然自定义了一个子类，完成了归还连接操作
• 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，所以继承这种方式行不通

• 装饰设计模式归还数据库连接的思想

• 我们可以自定义一个类，实现Connection接口
• 这样就具备了和JDBC4Connection相同的行为了
• 重写close()方法，完成连接的归还
• 其余的功能还调用mysql驱动包实现类原有的方法即可

• 装饰设计模式归还数据库连接的实现步骤

• 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成员变量
• 3.通过有参构造方法完成对成员变量的赋值
• 4.重写close()方法，将连接对象添加到池中
• 5.剩余方法，只需要调用mysql驱动包的连接对象完成即可
• 6.在自定义连接池中，将获取的连接对象通过自定义连接对象进行包装

• 装饰设计模式归还数据库连接存在的问题

• 实现Connection接口后
• 有大量的方法需要在自定义类中重写

• 装饰设计模式归还实例演示

• 

• package demo02.myDataSourse;
  
  import java.sql.*;
  import java.util.List;
  import java.util.Map;
  import java.util.Properties;
  import java.util.concurrent.Executor;
      //1.定义一个类，实现Connection接口
  public class demomyConnection implements Connection {
      //2.定义连接对象和连接池容器对象的成员变量
      private Connection con;
      private List pool;
      //3.通过有参构造方法为成员变量赋值
      public demomyConnection(Connection con, List pool) {
          this.con = con;
          this.pool = pool;
      }
      //4.重写close方法，完成归还连接
      @Override
      public void close() throws SQLException {
          pool.add(con);
      }
      //5.剩余方法，还是调用原有的连接对象中的功能即可
      @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> getTypeMap() throws SQLException {
          return con.getTypeMap();
      }
  
      @Override
      public void setTypeMap(Map> 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 unwrap(Class iface) throws SQLException {
          return con.unwrap(iface);
      }
  
      @Override
      public boolean isWrapperFor(Class iface) throws SQLException {
          return con.isWrapperFor(iface);
      }
  }

• 

• package demo02.myDataSourse;
  import demo02.utils.JDBCUtils;
  
  import javax.sql.DataSource;
  import java.io.PrintWriter;
  import java.sql.Connection;
  import java.sql.SQLException;
  import java.sql.SQLFeatureNotSupportedException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.logging.Logger;
  
  //自定义数据库连接池
  public class demoDataSourse implements DataSource{
      //1.准备容器，用于保存多个连接对象
      private static List pool = Collections.synchronizedList(new ArrayList<>());
      //2.定义静态代码块，通过工具类获取10个连接对象
      static{
          for(int i=1;i<=10;i++){
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
      //3.重写getConnection(),用于获取一个连接对象
      @Override
      public Connection getConnection() throws SQLException {
          if(pool.size()>0){
              Connection con = pool.remove(0);
              //通过自定义的连接对象，对原有的连接对象进行包装
              demomyConnection mycon = new demomyConnection(con,pool);
              return mycon;
          }else{
              throw new RuntimeException("连接数量已用尽");
          }
      }
      //4.定义getSize方法，获取连接池容器的大小
      public int getSize(){
          return pool.size();
      }
      @Override
      public Connection getConnection(String username, String password) throws SQLException {
          return null;
      }
  
      @Override
      public  T unwrap(Class 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;
      }
  }

• 

• package demo02.myDataSourse;
  
  import java.sql.Connection;
  import java.sql.PreparedStatement;
  import java.sql.ResultSet;
  
  public class demoDataSourseTest {
      public static void main(String[] args) throws Exception {
          //1.创建连接池对象
          demoDataSourse dataSourse = new demoDataSourse();
  
          System.out.println("使用之前的数量" + dataSourse.getSize());
  
          //2.通过连接池对象获取连接对象
          Connection con = dataSourse.getConnection();
          //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，进行归还
  
          System.out.println("使用之后的数量" + dataSourse.getSize());
      }
  }