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Java example source code file (StackTraceElements.java)

This example Java source code file (StackTraceElements.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

class, concurrenthashmap, concurrentmap, empty_inmemory_stack_trace, empty_stack_trace, inmemorystacktraceelement, integer, linenumbers, loadingcache, object, override, reflection, stacktraceelement, string, threading, threads, unknown_source

The StackTraceElements.java Java example source code

/**
 * Copyright (C) 2006 Google Inc.
 *
 * Licensed 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 com.google.inject.internal.util;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Member;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * Creates stack trace elements for members.
 *
 * @author crazybob@google.com (Bob Lee)
 */
public class StackTraceElements {

  private static final StackTraceElement[] EMPTY_STACK_TRACE = new StackTraceElement[0];
  private static final InMemoryStackTraceElement[] EMPTY_INMEMORY_STACK_TRACE = 
      new InMemoryStackTraceElement[0];

  /*if[AOP]*/
  static final LoadingCache<Class lineNumbersCache =
      CacheBuilder.newBuilder().weakKeys().softValues().build(
          new CacheLoader<Class() {
            public LineNumbers load(Class<?> key) {
              try {
                return new LineNumbers(key);
              }
              catch (IOException e) {
                throw new RuntimeException(e);
              }
            }
          });
  /*end[AOP]*/

  private static final ConcurrentMap<InMemoryStackTraceElement, InMemoryStackTraceElement>
      elementCache = new ConcurrentHashMap<InMemoryStackTraceElement, InMemoryStackTraceElement>();
  private static final ConcurrentMap<String, String> stringCache =
      new ConcurrentHashMap<String, String>();

  private static final String UNKNOWN_SOURCE = "Unknown Source";

  public static Object forMember(Member member) {
    if (member == null) {
      return SourceProvider.UNKNOWN_SOURCE;
    }

    Class declaringClass = member.getDeclaringClass();

    /*if[AOP]*/
    LineNumbers lineNumbers = lineNumbersCache.getUnchecked(declaringClass);
    String fileName = lineNumbers.getSource();
    Integer lineNumberOrNull = lineNumbers.getLineNumber(member);
    int lineNumber = lineNumberOrNull == null ? lineNumbers.getFirstLine() : lineNumberOrNull;
    /*end[AOP]*/
    /*if[NO_AOP]
    String fileName = null;
    int lineNumber = -1;
    end[NO_AOP]*/

    Class<? extends Member> memberType = Classes.memberType(member);
    String memberName = memberType == Constructor.class ? "<init>" : member.getName();
    return new StackTraceElement(declaringClass.getName(), memberName, fileName, lineNumber);
  }

  public static Object forType(Class<?> implementation) {
    /*if[AOP]*/
    LineNumbers lineNumbers = lineNumbersCache.getUnchecked(implementation);
    int lineNumber = lineNumbers.getFirstLine();
    String fileName = lineNumbers.getSource();
    /*end[AOP]*/
    /*if[NO_AOP]
    String fileName = null;
    int lineNumber = -1;
    end[NO_AOP]*/

    return new StackTraceElement(implementation.getName(), "class", fileName, lineNumber);
  }
  
  /**
   * Clears the internal cache for {@link StackTraceElement StackTraceElements}.
   */
  public static void clearCache() {
    elementCache.clear();
    stringCache.clear();
  }
  
  /**
   * Returns encoded in-memory version of {@link StackTraceElement StackTraceElements}.
   */
  public static InMemoryStackTraceElement[] convertToInMemoryStackTraceElement(
      StackTraceElement[] stackTraceElements) {
    if (stackTraceElements.length == 0) {
      return EMPTY_INMEMORY_STACK_TRACE;
    }
    InMemoryStackTraceElement[] inMemoryStackTraceElements = 
        new InMemoryStackTraceElement[stackTraceElements.length];
    for (int i = 0; i < stackTraceElements.length; i++) {
      inMemoryStackTraceElements[i] = 
          weakIntern(new InMemoryStackTraceElement(stackTraceElements[i]));
    }
    return inMemoryStackTraceElements;
  }
  
  /**
   * Decodes in-memory stack trace elements to regular {@link StackTraceElement StackTraceElements}.
   */
  public static StackTraceElement[] convertToStackTraceElement(
      InMemoryStackTraceElement[] inMemoryStackTraceElements) {
    if (inMemoryStackTraceElements.length == 0) {
      return EMPTY_STACK_TRACE;
    }
    StackTraceElement[] stackTraceElements = 
        new StackTraceElement[inMemoryStackTraceElements.length];
    for (int i = 0; i < inMemoryStackTraceElements.length; i++) {
      String declaringClass = inMemoryStackTraceElements[i].getClassName();
      String methodName = inMemoryStackTraceElements[i].getMethodName();
      int lineNumber = inMemoryStackTraceElements[i].getLineNumber();
      stackTraceElements[i] = 
          new StackTraceElement(declaringClass, methodName, UNKNOWN_SOURCE, lineNumber);
    }
    return stackTraceElements;
  }
  
  private static InMemoryStackTraceElement weakIntern(
      InMemoryStackTraceElement inMemoryStackTraceElement) {
    InMemoryStackTraceElement cached = elementCache.get(inMemoryStackTraceElement);
    if (cached != null) {
      return cached;
    }
    inMemoryStackTraceElement = new InMemoryStackTraceElement(
        weakIntern(inMemoryStackTraceElement.getClassName()), 
        weakIntern(inMemoryStackTraceElement.getMethodName()), 
        inMemoryStackTraceElement.getLineNumber());
    elementCache.put(inMemoryStackTraceElement, inMemoryStackTraceElement);
    return inMemoryStackTraceElement;
  }
  
  private static String weakIntern(String s) {
    String cached = stringCache.get(s);
    if (cached != null) {
      return cached;
    }
    stringCache.put(s, s);
    return s;
  }
  
  /**
   * In-Memory version of {@link StackTraceElement} that does not store the file name. 
   */
  public static class InMemoryStackTraceElement {
    private String declaringClass;
    private String methodName;
    private int lineNumber;

    InMemoryStackTraceElement(StackTraceElement ste) {
      this(ste.getClassName(), ste.getMethodName(), ste.getLineNumber());
    }

    InMemoryStackTraceElement(String declaringClass, String methodName, int lineNumber) {
      this.declaringClass = declaringClass;
      this.methodName = methodName;
      this.lineNumber = lineNumber;
    }

    String getClassName() {
      return declaringClass;
    }
    
    String getMethodName() {
      return methodName;
    }
    
    int getLineNumber() {
      return lineNumber;
    }

    @Override
    public boolean equals(Object obj) {
      if (obj == this) {
        return true;
      }
      if (!(obj instanceof InMemoryStackTraceElement)) {
        return false;
      }
      InMemoryStackTraceElement e = (InMemoryStackTraceElement) obj;
      return e.declaringClass.equals(declaringClass) && e.lineNumber == lineNumber && 
          methodName.equals(e.methodName);
    }

    @Override
    public int hashCode() {
      int result = 31 * declaringClass.hashCode() + methodName.hashCode();
      result = 31 * result + lineNumber;
      return result;
    }
    
    @Override
    public String toString() {
      return declaringClass + "." + methodName + "(" + lineNumber + ")";
    }
  }
}

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