java - 编写自定义 Flume 装饰器，但出现错误。我错过了什么？

Question

我正在为 Cloudera 的分布式日志聚合系统 Flume 编写自定义装饰器插件。我的 Java 代码如下:

package multiplex;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import com.cloudera.flume.conf.Context;
import com.cloudera.flume.conf.SinkFactory.SinkDecoBuilder;
import com.cloudera.flume.core.Event;
import com.cloudera.flume.core.EventImpl;
import com.cloudera.flume.core.EventSink;
import com.cloudera.flume.core.EventSinkDecorator;
import com.cloudera.util.Pair;
import com.google.common.base.Preconditions;

public class JsonMultiplexDecorator<S extends EventSink> extends EventSinkDecorator<S> {
  private final String serverName;
  private final String logType;

  public JsonMultiplexDecorator(S s, String serverName, String logType) {
    super(s);

    this.serverName = serverName;
    this.logType = logType;
  }

  @Override
  public void append(Event e) throws IOException {
    String body = new String(e.getBody()).replaceAll("\"", "\\\"");

    String json = "{ \"server\": \"" + this.serverName + "\"," +
      "\"log_type\": \"" + this.logType + "\", " +
      "\"body\": \"" + body + "\" }";

    EventImpl e2 = new EventImpl(json.getBytes(),
        e.getTimestamp(), e.getPriority(), e.getNanos(), e.getHost(),
        e.getAttrs());

    super.append(e2);
  }

  public static SinkDecoBuilder builder() {
    return new SinkDecoBuilder() {
      @Override
      public EventSinkDecorator<EventSink> build(Context context,
          String... argv) {
        Preconditions.checkArgument(argv.length == 2,
            "usage: multiplexDecorator(serverName, logType)");

        return new JsonMultiplexDecorator<EventSink>(null, argv[0], argv[1]);
      }
    };
  }

  public static List<Pair<String, SinkDecoBuilder>> getDecoratorBuilders() {
    List<Pair<String, SinkDecoBuilder>> builders = 
      new ArrayList<Pair<String, SinkDecoBuilder>>();

    builders.add(new Pair<String, SinkDecoBuilder>("jsonMultiplexDecorator", builder()));

    return builders;
  }
}

这可以用 ant 很好地编译成 JAR 文件，我可以在运行时将它加载到 Flume 中并成功配置节点以使用它。但是，当一个事件实际发生在加载了这个插件的节点上时，我的日志中会出现这样的错误:

2010-10-19 21:03:15,176 [logicalNode xxxxx] ERROR connector.DirectDriver: Driving src/sink failed! LazyOpenSource | LazyOpenDecorator because null
java.lang.UnsupportedOperationException
    at java.util.Collections$UnmodifiableMap.put(Collections.java:1285)
    at com.cloudera.flume.core.EventBaseImpl.set(EventBaseImpl.java:65)
    at com.cloudera.flume.handlers.rolling.RollSink.append(RollSink.java:164)
    at com.cloudera.flume.agent.diskfailover.DiskFailoverDeco.append(DiskFailoverDeco.java:93)
    at com.cloudera.flume.core.BackOffFailOverSink.append(BackOffFailOverSink.java:144)
    at com.cloudera.flume.agent.AgentSink.append(AgentSink.java:109)
    at com.cloudera.flume.core.EventSinkDecorator.append(EventSinkDecorator.java:58)
    at multiplex.JsonMultiplexDecorator.append(JsonMultiplexDecorator.java:56)
    at com.cloudera.flume.core.EventSinkDecorator.append(EventSinkDecorator.java:58)
    at com.cloudera.flume.handlers.debug.LazyOpenDecorator.append(LazyOpenDecorator.java:69)
    at com.cloudera.flume.core.connector.DirectDriver$PumperThread.run(DirectDriver.java:92)

([logicalNode xxxxx] 是 EC2 内部 DNS 名称的占位符)。我没有很多 Java 经验，所以我不确定我是否在这里做错了什么，或者这是一个 Flume 错误。我应该提一下，我使用 Flume 源代码中的 HelloWorld 插件示例编写了这篇文章，并且还借鉴了一些内置的 Flume 装饰器。

Answer 1

当您构造 EventImpl e2 时，您正在传递 e.getAttrs()，这是不可修改的。尝试将 e.getAttrs() 复制到您自己的 map 中；使用 new HashMap(e.getAttrs()) 的浅拷贝就足够了。

引用:https://groups.google.com/a/cloudera.org/group/flume-user/browse_thread/thread/046b4a446877c8f9?pli=1