| /* |
| * 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.lang.reflect.Constructor; |
| |
| import org.apache.commons.logging.Log; |
| import org.apache.commons.logging.LogFactory; |
| |
| /** |
| * Extremely simple callback to determine the frequency that an action should |
| * be performed. |
| * |
| * <p>For example, the next() function may look like this:</p> |
| * <pre> |
| * <code> |
| * public boolean next() { |
| * return Math.random() > 0.5; |
| * } |
| * </code> |
| * </pre> |
| * <p>This would trace 50% of all gets, 75% of all puts and would not trace any |
| * other requests.</p> |
| */ |
| public abstract class Sampler { |
| /** |
| * A {@link Sampler} builder. It takes a {@link Sampler} 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); |
| |
| private final static String DEFAULT_PACKAGE = "org.apache.htrace.core"; |
| private final HTraceConfiguration conf; |
| private String className; |
| private ClassLoader classLoader = Builder.class.getClassLoader(); |
| |
| public Builder(HTraceConfiguration conf) { |
| this.conf = conf; |
| reset(); |
| } |
| |
| public Builder reset() { |
| this.className = null; |
| return this; |
| } |
| |
| public Builder className(String className) { |
| this.className = className; |
| return this; |
| } |
| |
| public Builder classLoader(ClassLoader classLoader) { |
| this.classLoader = classLoader; |
| return this; |
| } |
| |
| private void throwError(String errorStr) { |
| LOG.error(errorStr); |
| throw new RuntimeException(errorStr); |
| } |
| |
| private void throwError(String errorStr, Throwable e) { |
| LOG.error(errorStr, e); |
| throw new RuntimeException(errorStr, e); |
| } |
| |
| public Sampler build() { |
| Sampler sampler = newSampler(); |
| if (LOG.isTraceEnabled()) { |
| LOG.trace("Created new sampler of type " + |
| sampler.getClass().getName(), new Exception()); |
| } |
| return sampler; |
| } |
| |
| private Sampler newSampler() { |
| if (className == null || className.isEmpty()) { |
| throwError("No sampler 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 Sampler class " + str); |
| } |
| Constructor<Sampler> ctor = null; |
| try { |
| ctor = cls.getConstructor(HTraceConfiguration.class); |
| } catch (NoSuchMethodException e) { |
| throwError("Cannot find a constructor for class " + |
| str + " which takes an HTraceConfiguration."); |
| } |
| Sampler sampler = null; |
| try { |
| LOG.debug("Creating new instance of " + str + "..."); |
| sampler = ctor.newInstance(conf); |
| } catch (ReflectiveOperationException e) { |
| throwError("Reflection error when constructing " + |
| str + ".", e); |
| } catch (Throwable t) { |
| throwError("NewInstance error when constructing " + |
| str + ".", t); |
| } |
| return sampler; |
| } |
| } |
| |
| public static final Sampler ALWAYS = AlwaysSampler.INSTANCE; |
| public static final Sampler NEVER = NeverSampler.INSTANCE; |
| |
| public abstract boolean next(); |
| } |