Morphia客户端连接MongoDB，设连接池为1仍多连接，如何解决？

测试Morphia客户端连接MongoDB时，已将连接池的minSize和maxSize均设置为1，但客户端仍创建多个连接，需要找到正确限制连接数为1的配置方法。

相关代码 #

public static void main(String[] args) {
        ConnectionPoolSettings connectionPoolSettings = ConnectionPoolSettings.builder().minSize(1).maxSize(1).build();

        MongoClient client = MongoClients.create( MongoClientSettings
                        .builder()
                        .applyConnectionString(new ConnectionString("mongodb://localhost:27017/test"))
                        .applyToConnectionPoolSettings(builder -> builder.applySettings(connectionPoolSettings))
                        .build());
        MongoDatabase database = client.getDatabase("admin");
        Document serverStatus = database.runCommand(new Document("serverStatus", 1));

        new Thread(() -> {
            while(true) {
                Map connections = (Map) serverStatus.get("connections");
                System.out.println("Number of connections " + connections.get("current"));
                try {
                    TimeUnit.SECONDS.sleep(10);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        }).start();
        try {

            while(true)
                TimeUnit.SECONDS.sleep(60);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

netstat命令输出 #

raaghu@FVFH8ET1Q05D ~ % netstat -anv | awk '$5 ~ "27017" {print}'| grep ESTABLISHED
tcp4       0      0  127.0.0.1.57851        127.0.0.1.27017        ESTABLISHED  337773  146988  27252      0 00002 00000008 000000000008ef3a 00000080 00000800      1      0 000001
tcp4       0      0  127.0.0.1.57850        127.0.0.1.27017        ESTABLISHED  407373  146988  27252      0 00002 00000008 000000000008ef21 00000080 00000800      1      0 000001
tcp4       0      0  127.0.0.1.57849        127.0.0.1.27017        ESTABLISHED  407373  146988  27252      0 00002 00000008 000000000008ef20 00000080 00000800      1      0 000001

1. 先修复连接数监控的代码问题 #

你当前只在程序启动时获取了一次serverStatus文档，后续循环打印的都是旧数据，根本无法反映实时连接数。要把获取服务器状态的逻辑放到循环里：

new Thread(() -> {
    while(true) {
        Document serverStatus = database.runCommand(new Document("serverStatus", 1));
        Map connections = (Map) serverStatus.get("connections");
        System.out.println("Number of connections " + connections.get("current"));
        try {
            TimeUnit.SECONDS.sleep(10);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
}).start();

2. 优化连接池配置方式 #

你用applySettings覆盖连接池配置的方式容易出现参数覆盖不全的问题，建议直接在applyToConnectionPoolSettings中直接设置参数，同时补充空闲连接超时配置，避免闲置连接被误创建：

MongoClient client = MongoClients.create(MongoClientSettings
        .builder()
        .applyConnectionString(new ConnectionString("mongodb://localhost:27017/test"))
        .applyToConnectionPoolSettings(poolBuilder -> {
            poolBuilder.minSize(1);
            poolBuilder.maxSize(1);
            // 设置空闲连接超时，避免闲置连接占用资源
            poolBuilder.maxConnectionIdleTime(60, TimeUnit.SECONDS);
            // 设置连接生命周期，强制替换旧连接
            poolBuilder.maxConnectionLifeTime(300, TimeUnit.SECONDS);
        })
        .build());

3. 关闭驱动的内部监控连接 #

MongoDB Java驱动默认会创建独立的监控连接用于采集服务器状态，这部分连接不计入连接池的maxSize限制。如果要彻底把总连接数限制为1，需要关闭这个监控功能：

MongoClient client = MongoClients.create(MongoClientSettings
        .builder()
        .applyConnectionString(new ConnectionString("mongodb://localhost:27017/test"))
        .applyToConnectionPoolSettings(poolBuilder -> {
            poolBuilder.minSize(1);
            poolBuilder.maxSize(1);
        })
        // 关闭服务器监控连接
        .applyToClusterSettings(clusterBuilder -> {
            clusterBuilder.serverMonitorListener((ServerMonitorListener) null);
        })
        .build());

4. 确认Morphia的使用规范 #

如果是通过Morphia的Datastore操作数据库，必须确保复用同一个MongoClient实例——每个MongoClient都会维护自己独立的连接池，多实例会直接导致连接数翻倍。

修改完成后重新运行程序，再用netstat查看连接状态，就能看到只有1个ESTABLISHED状态的连接了。

内容的提问来源于stack exchange，提问作者Raaghu