htrace-core4/src/main/java/org/apache/htrace/core/SpanReceiver.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.htrace.core;

import java.io.Closeable;
import java.lang.reflect.Constructor;
import java.util.concurrent.atomic.AtomicLong;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * The collector within a process that is the destination of Spans when a
 * trace is running. {@code SpanReceiver} implementations are expected to
 * provide a constructor with the signature
 *
 * <pre>
 * <code>public SpanReceiverImpl(HTraceConfiguration)</code>
 * </pre>
 */
public abstract class SpanReceiver implements Closeable {
  /**
   * A {@link SpanReceiver} builder. It takes a {@link SpanReceiver} class name
   * and constructs an instance of that class, with the provided configuration.
   */
  public static class Builder {
    private static final Log LOG = LogFactory.getLog(Builder.class);

    final static String DEFAULT_PACKAGE = "org.apache.htrace.core";
    private final HTraceConfiguration conf;
    private boolean logErrors;
    private String className;
    private ClassLoader classLoader = Builder.class.getClassLoader();

    public Builder(HTraceConfiguration conf) {
      this.conf = conf;
      reset();
    }

    /**
     * Set this builder back to defaults.
     *
     * @return this instance.
     */
    public Builder reset() {
      this.logErrors = true;
      this.className = null;
      return this;
    }

    public Builder className(final String className) {
      this.className = className;
      return this;
    }

    /**
     * Configure whether we should log errors during build().
     *
     * @param logErrors Whether we should log errors during build().
     * @return This instance
     */
    public Builder logErrors(boolean logErrors) {
      this.logErrors = logErrors;
      return this;
    }

    public Builder classLoader(ClassLoader classLoader) {
      this.classLoader = classLoader;
      return this;
    }

    private void throwError(String errorStr) {
      if (logErrors) {
        LOG.error(errorStr);
      }
      throw new RuntimeException(errorStr);
    }

    private void throwError(String errorStr, Throwable e) {
      if (logErrors) {
        LOG.error(errorStr, e);
      }
      throw new RuntimeException(errorStr, e);
    }

    public SpanReceiver build() {
      SpanReceiver spanReceiver = newSpanReceiver();
      if (LOG.isTraceEnabled()) {
        LOG.trace("Created new span receiver of type " +
                  spanReceiver.getClass().getName());
      }
      return spanReceiver;
    }

    private SpanReceiver newSpanReceiver() {
      if ((className == null) || className.isEmpty()) {
        throwError("No span receiver class specified.");
      }
      String str = className;
      if (!str.contains(".")) {
        str = DEFAULT_PACKAGE + "." + str;
      }
      Class cls = null;
      try {
        cls = classLoader.loadClass(str);
      } catch (ClassNotFoundException e) {
        throwError("Cannot find SpanReceiver class " + str);
      }
      Constructor<SpanReceiver> ctor = null;
      try {
        ctor = cls.getConstructor(HTraceConfiguration.class);
      } catch (NoSuchMethodException e) {
        throwError("Cannot find a constructor for class " +
            str + "which takes an HTraceConfiguration.");
      }
      SpanReceiver receiver = null;
      try {
        LOG.debug("Creating new instance of " + str + "...");
        receiver = ctor.newInstance(conf);
      } catch (ReflectiveOperationException e) {
        throwError("Reflection error when constructing " +
            str + ".", e);
      } catch (Throwable t) {
        throwError("NewInstance error when constructing " +
            str + ".", t);
      }
      return receiver;
    }
  }

  /**
   * An ID which uniquely identifies this SpanReceiver.
   */
  private final long id;

  private static final AtomicLong HIGHEST_SPAN_RECEIVER_ID = new AtomicLong(0);

  /**
   * Get the ID for this SpanReceiver.
   *
   * @return The unique ID identifying this SpanReceiver.
   */
  public final long getId() {
    return id;
  }

  protected SpanReceiver() {
    this.id = HIGHEST_SPAN_RECEIVER_ID.incrementAndGet();
  }

  /**
   * Called when a Span is stopped and can now be stored.
   *
   * @param span    The span to store with this SpanReceiver.
   */
  public abstract void receiveSpan(Span span);
}