背景介绍

在一次druid数据库连接池连接泄露的排查分析介绍了连接泄露的分析排查过程，但是对造成连接泄露的场景描述的不是太详细，下面通过代码的方式来复现连接泄露的case。

复现过程

连接泄露场景

模拟了在设置了phyTimeoutMillis参数情况下，连接泄露的场景。

连接泄露模拟代码

import com.alibaba.druid.pool.DruidConnectionHolder;
import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.pool.DruidPooledConnection;

import java.util.List;
import java.util.Map;

public class DruidAbandonedCase4PhyTimeout {
    public static void main(String[] args) throws Exception{
        DruidDataSource dataSource =  new DruidDataSource();
        dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
        dataSource.setUsername("root");
        dataSource.setPassword("123456");
        dataSource.setUrl("jdbc:mysql://127.0.0.1:3306/test?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8&useSSL=false");

        dataSource.setMinIdle(2);
        // 保证不会触发DestroyTask，以便手动调用shrink
        dataSource.setTimeBetweenEvictionRunsMillis(1 * 60 * 60 * 1000);
        // 物理连接超时时长(超过该阈值会close掉物理连接)
        dataSource.setPhyTimeoutMillis(1000);
        dataSource.setMinEvictableIdleTimeMillis(500);
        dataSource.setKeepAliveBetweenTimeMillis(501);

        dataSource.init();

        DruidPooledConnection connection1 = dataSource.getConnection();
        DruidConnectionHolder holder1 = connection1.getConnectionHolder();
        System.out.println(holder1);
        try{
            //假装该连接使用了500ms，要小于phyTimeoutMillis，以免归还连接的时候被discard了
            Thread.sleep(500L);
        }catch (Exception e){
            e.printStackTrace();
        }

        DruidPooledConnection connection2 = dataSource.getConnection();
        DruidConnectionHolder holder2 = connection2.getConnectionHolder();
        System.out.println(holder2);
        connection2.close();

        connection1.close();

        System.out.println("调用shrink【之前】，连接池中连接情况,begin");
        List<Map<String, Object>> conns = dataSource.getPoolingConnectionInfo();
        for(Map<String,Object> conn : conns){
            System.out.println(conn.get("id"));
        }
        System.out.println("调用shrink【之前】，连接池中连接情况,end");

        try{
            // 让连接1的物理连接时间超过phyTimeoutMillis，以观察连接1是否会被连接池释放掉
            Thread.sleep(501L);
        }catch (Exception e){
            e.printStackTrace();
        }

        System.out.println();
        System.out.println("物理连接时间,begin");
        long ctm = System.currentTimeMillis();
        System.out.println(holder1 + " phyConnectTimeMillis:" + (ctm - holder1.getConnectTimeMillis()) + " ,idleMillis:" + (ctm - holder1.getLastActiveTimeMillis()));
        System.out.println(holder2 + " phyConnectTimeMillis:" + (ctm - holder2.getConnectTimeMillis()) + " ,idleMillis:" + (ctm - holder2.getLastActiveTimeMillis()));
        System.out.println("物理连接时间,end");

        System.out.println();
        // 手动执行shrink
        dataSource.shrink(true);
        System.out.println("调用shrink【之后】，连接池中连接情况,begin");
        conns = dataSource.getPoolingConnectionInfo();
        for(Map<String,Object> conn : conns){
            System.out.println(conn.get("id"));
        }
        System.out.println("调用shrink【之后】，连接池中连接情况,end");

        System.out.println();

        System.out.println(holder1 + " isClosed:" + holder1.getConnection().isClosed());
        System.out.println(holder2 + " isClosed:" + holder2.getConnection().isClosed());
    }
}
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运行以上程序，输出结果如下：

{ID:26004719, ConnectTime:"2023-10-10 12:40:04", UseCount:1, LastActiveTime:"2023-10-10 12:40:04"}
{ID:31314834, ConnectTime:"2023-10-10 12:40:05", UseCount:1, LastActiveTime:"2023-10-10 12:40:05"}
调用shrink【之前】，连接池中连接情况,begin
31314834
26004719
调用shrink【之前】，连接池中连接情况,end

物理连接时间,begin
{ID:26004719, ConnectTime:"2023-10-10 12:40:04", UseCount:1, LastActiveTime:"2023-10-10 12:40:05"} phyConnectTimeMillis:1011 ,idleMillis:501
{ID:31314834, ConnectTime:"2023-10-10 12:40:05", UseCount:1, LastActiveTime:"2023-10-10 12:40:05"} phyConnectTimeMillis:502 ,idleMillis:501
物理连接时间,end

调用shrink【之后】，连接池中连接情况,begin
26004719
调用shrink【之后】，连接池中连接情况,end

{ID:26004719, ConnectTime:"2023-10-10 12:40:04", UseCount:1, LastActiveTime:"2023-10-10 12:40:05"} isClosed:true
{ID:31314834, ConnectTime:"2023-10-10 12:40:05", UseCount:1, LastActiveTime:"2023-10-10 12:40:05"} isClosed:false
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期望执行结果：
ID是26004719的连接应该从连接池中删除，ID是31314834的连接应该被连接池管理
实际执行结果：
ID是26004719的连接没有从连接池删除；ID是31314834的连接却从连接池删除了，且连接没有被关闭，即ID是31314834的连接既没有被连接池管理又没有被关闭，属于泄露的连接。

测试了druid 1.1.11，1.2.0，1.2.8 ~ 1.2.17，1.2.18~1.2.20，其中【1.1.11，1.2.0，1.2.8 ~ 1.2.17】都存在以上连接泄露的问题，1.2.18~1.2.20不存在以上连接泄露的问题了。