使用Eclipse Milo连接OPC UA服务器遇StacklessClosedChannelException求助

使用Eclipse Milo连接OPC UA服务器时抛出StacklessClosedChannelException异常，但OPCUA Explorer等客户端能正常连接并读取变量。

代码片段 #

int codMacchina = macchina.getCodMacchina();
String ipServer = macchina.getIpServer();
String porta = macchina.getPorta();
String username = macchina.getUsername();
String password = macchina.getPassword();

try {
    List<EndpointDescription> endpoints = 
    DiscoveryClient.getEndpoints("opc.tcp://" + ipServer + ":" + porta).get();
    EndpointDescription configPoint = endpoints.get(0);
   
    OpcUaClientConfigBuilder cfg = new OpcUaClientConfigBuilder();
    cfg.setEndpoint(configPoint);
    cfg.setIdentityProvider(new UsernameProvider(username, password));

    OpcUaClient client = OpcUaClient.create(cfg.build());
    CompletableFuture<UaClient> cf = client.connect();
    cf.get();

.....

堆栈跟踪 #

[2023-06-13][15:16:28:847][ERROR][AbstractLoggingWriter][71][java.util.concurrent.ExecutionException: io.netty.channel.StacklessClosedChannelException
]
[2023-06-13][15:16:28:885][ERROR][AbstractLoggingWriter][71][   at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:395)
]
[2023-06-13][15:16:28:899][ERROR][AbstractLoggingWriter][71][   at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1999)
]
[2023-06-13][15:16:28:913][ERROR][AbstractLoggingWriter][71][   at deployment.GnuttiHubEar.ear.GnuttiHub.war//it.gnuttihub.job.ImportaDatiOPCUAJob.lambda$0(ImportaDatiOPCUAJob.java:70)
]
[2023-06-13][15:16:28:932][ERROR][AbstractLoggingWriter][71][   at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1654)
]
[2023-06-13][15:16:28:947][ERROR][AbstractLoggingWriter][71][   at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:658)
]
[2023-06-13][15:16:28:961][ERROR][AbstractLoggingWriter][71][   at deployment.GnuttiHubEar.ear.GnuttiHub.war//it.gnuttihub.job.ImportaDatiOPCUAJob.executeJob(ImportaDatiOPCUAJob.java:53)
]
[2023-06-13][15:16:28:974][ERROR][AbstractLoggingWriter][71][   at deployment.GnuttiHubEar.ear.GnuttiHub.war//it.gnuttihub.job.AbstractJob.execute(AbstractJob.java:24)
]
[2023-06-13][15:16:28:988][ERROR][AbstractLoggingWriter][71][   at deployment.GnuttiHubEar.ear.GnuttiHub.war//org.quartz.core.JobRunShell.run(JobRunShell.java:202)
]
[2023-06-13][15:16:29:001][ERROR][AbstractLoggingWriter][71][   at deployment.GnuttiHubEar.ear.GnuttiHub.war//org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573)
]
[2023-06-13][15:16:29:018][ERROR][AbstractLoggingWriter][71][Caused by: io.netty.channel.StacklessClosedChannelException
]
[2023-06-13][15:16:29:031][ERROR][AbstractLoggingWriter][71][   at io.netty.channel.AbstractChannel$AbstractUnsafe.ensureOpen(ChannelPromise)(Unknown Source)]

• 端点选择不匹配：直接取endpoints.get(0)可能选中了服务器不兼容的端点（如安全策略、加密方式不匹配）。OPCUA Explorer会自动筛选兼容端点，建议遍历所有端点，打印其安全策略、消息模式，选择与OPCUA Explorer一致的端点。
• Netty版本冲突：Milo对Netty版本有严格依赖，项目中若存在冲突的Netty版本，会导致通道异常。通过Maven/Gradle依赖树排查，排除冲突的Netty依赖，保持与Milo依赖版本一致。
• 同步阻塞导致超时：cf.get()会同步阻塞线程，若服务器响应慢或网络波动，易引发通道关闭。建议改用异步回调处理连接结果，或设置超时时间：cf.get(5, TimeUnit.SECONDS)。
• 安全配置缺失：部分服务器要求特定安全配置，比如信任服务器证书。Milo默认证书处理逻辑与OPCUA Explorer不同，可手动配置证书验证（测试环境可临时跳过）：

  cfg.setCertificateValidator(new CertificateValidator() {
      @Override
      public void validateCertificate(X509Certificate certificate) throws CertificateValidationException {
          // 测试环境下跳过证书校验
      }
  });
  

• 客户端生命周期问题：若OpcUaClient为局部变量，可能被提前GC导致通道关闭。建议将其声明为类成员变量，确保实例被正确持有。

内容的提问来源于stack exchange，提问作者Giuseppe Castellano