tomcat自定义classloader

Question

对class文件加密，然后自定义classloader，tomcat启动时调用该classloader加载加密的class文件，最好有详细代码

Answer 1

大概分两步：

1.对class文件进行加密

2.写解密class文件并加载的classloader

3.将这个classloader加入到tomcat中，也就是使tomcat可以调用到这个classloader

【加密】

1.思路

字节流读取class文件，进行简单的移位

2.实现

做了一个小程序，实现了对某文件夹下所有class文件字节流读取，并+2位的加密方式

3.说明

swing是使用myeclipse的插件做的，可能比较乱

4.代码&下载

源代码和程序打包成jar文件上传到了这里，双击可以使用。

【classloader】

[java] view plaincopy在CODE上查看代码片派生到我的代码片
package com.uikoo9;

import java.io.ByteArrayOutputStream;

import java.io.FileInputStream;

import java.io.IOException;

import org.apache.catalina.loader.WebappClassLoader;

/**

• 自己的ClassLoader
• 用于解密加密过的class文件并加载

• @author uikoo9
  */
  
  public class MyClassLoader extends WebappClassLoader{

  /**

  • 默认构造器 */
    public MyClassLoader() {
    super();
    }
    

  /**

  • 默认构造器
  • @param parent */
    public MyClassLoader(ClassLoader parent) {
    super(parent);
    }
    

  /* (non-Javadoc)

  • @see org.apache.catalina.loader.WebappClassLoader#findClass(java.lang.String)
    */
    
    public Class<?> findClass(String name) throws ClassNotFoundException {
    
    byte[] classBytes = null;

    try {
    
    classBytes = loadClassBytes(name);
    
    } catch (Exception e) {
    
    throw new ClassNotFoundException(name);
    
    }

    Class<?> cl= defineClass(name, classBytes, 0, classBytes.length);
    
    if(cl == null) throw new ClassNotFoundException(name);

    return cl;
    
    }

  /**

  • 简单的解密
  • @param name
  • @return

  • @throws IOException
    */
    
    private byte[] loadClassBytes(String name) throws IOException{
    
    String cname = name.replace('.', '/') + ".class";

    FileInputStream in = new FileInputStream(cname);
    
    try {
    
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();

    int ch;  
    while((ch = in.read()) != -1){  
        if(cname.contains("uikoo9")){// 如果包含uikoo9说明是自己写的class，进行解密  
            System.out.println("++");  
            buffer.write((byte)(ch-2));  
        }else{  
            buffer.write((byte)ch);  
        }  
    }  
    in.close();  
    
    return buffer.toByteArray();  
    

    }finally{
    
    in.close();
    
    }
    
    }
    
    }

【加入到tomcat中】
1.网上

网上很多文章都问到tomcat怎么使用自己的classloader，但是说明白的几乎没有，

最后自己读了tomcat官网的文档，找到了答案，

地址：http://tomcat.apache.org/tomcat-6.0-doc/config/loader.html

2.方法

说简单点，就是在tomcat\conf\context.xml中添加以下这段代码：

[html] view plaincopy在CODE上查看代码片派生到我的代码片


3.classloader
但是注意，这里的com.uikoo9.MyClassLoader并不是项目中的，

而是需要放到tomcat\lib下。

【新的问题】

1.这个自己写的classloader确实起作用的，但是问题也随之而来，

原来tomcat在调用classloader之前会调用一个自己的classparser类来对class文件进行解析

2.classparser

位于org\apache\tomcat\util\bcel\classfile下的ClassParser.java，

源代码：

[java] view plaincopy在CODE上查看代码片派生到我的代码片
/*

• 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.tomcat.util.bcel.classfile;
  

import java.io.BufferedInputStream;

import java.io.DataInputStream;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.util.zip.ZipEntry;

import java.util.zip.ZipFile;

import org.apache.tomcat.util.bcel.Constants;

/**

• Wrapper class that parses a given Java .class file. The method <A
• href ="#parse">parse returns a
• JavaClass object on success. When an I/O error or an
• inconsistency occurs an appropiate exception is propagated back to
• the caller.
• The structure and the names comply, except for a few conveniences,
• exactly with the
• JVM specification 1.0. See this paper for
• further details about the structure of a bytecode file.
• @version $Id: ClassParser.java 992409 2010-09-03 18:35:59Z markt $

• @author M. Dahm
  
  */
  
  public final class ClassParser {

  private DataInputStream file;
  
  private boolean fileOwned;
  
  private String file_name;
  
  private String zip_file;
  
  private int class_name_index, superclass_name_index;
  
  private int major, minor; // Compiler version
  
  private int access_flags; // Access rights of parsed class
  
  private int[] interfaces; // Names of implemented interfaces
  
  private ConstantPool constant_pool; // collection of constants
  
  private Field[] fields; // class fields, i.e., its variables
  
  private Method[] methods; // methods defined in the class
  
  private Attribute[] attributes; // attributes defined in the class
  
  private boolean is_zip; // Loaded from zip file
  
  private static final int BUFSIZE = 8192;

  /**

  • Parse class from the given stream.
  • @param file Input stream
  • @param file_name File name */
    public ClassParser(InputStream file, String file_name) {
    this.file_name = file_name;
    fileOwned = false;
    String clazz = file.getClass().getName(); // Not a very clean solution ...
    is_zip = clazz.startsWith("java.util.zip.") || clazz.startsWith("java.util.jar.");
    if (file instanceof DataInputStream) {
    this.file = (DataInputStream) file;
    } else {
    this.file = new DataInputStream(new BufferedInputStream(file, BUFSIZE));
    }
    }
    

  /**

  • Parse the given Java class file and return an object that represents
  • the contained data, i.e., constants, methods, fields and commands.
  • A ClassFormatException is raised, if the file is not a valid
  • .class file. (This does not include verification of the byte code as it
  • is performed by the java interpreter).
  • @return Class object representing the parsed class file
  • @throws IOException

  • @throws ClassFormatException
    */
    
    public JavaClass parse() throws IOException, ClassFormatException {
    
    ZipFile zip = null;
    
    try {
    
    if (fileOwned) {
    
    if (is_zip) {
    
    zip = new ZipFile(zip_file);
    
    ZipEntry entry = zip.getEntry(file_name);

            if (entry == null) {  
                throw new IOException("File " + file_name + " not found");  
            }  
    
            file = new DataInputStream(new BufferedInputStream(zip.getInputStream(entry),  
                    BUFSIZE));  
        } else {  
            file = new DataInputStream(new BufferedInputStream(new FileInputStream(  
                    file_name), BUFSIZE));  
        }  
    }  
    /****************** Read headers ********************************/  
    // Check magic tag of class file  
    readID();  
    // Get compiler version  
    readVersion();  
    /****************** Read constant pool and related **************/  
    // Read constant pool entries  
    readConstantPool();  
    // Get class information  
    readClassInfo();  
    // Get interface information, i.e., implemented interfaces  
    readInterfaces();  
    /****************** Read class fields and methods ***************/  
    // Read class fields, i.e., the variables of the class  
    readFields();  
    // Read class methods, i.e., the functions in the class  
    readMethods();  
    // Read class attributes  
    readAttributes();  
    // Check for unknown variables  
    //Unknown[] u = Unknown.getUnknownAttributes();  
    //for(int i=0; i < u.length; i++)  
    //  System.err.println("WARNING: " + u[i]);  
    // Everything should have been read now  
    //      if(file.available() > 0) {  
    //        int bytes = file.available();  
    //        byte[] buf = new byte[bytes];  
    //        file.read(buf);  
    //        if(!(is_zip && (buf.length == 1))) {  
    //          System.err.println("WARNING: Trailing garbage at end of " + file_name);  
    //          System.err.println(bytes + " extra bytes: " + Utility.toHexString(buf));  
    //        }  
    //      }  
    

    } finally {
    
    // Read everything of interest, so close the file
    
    if (fileOwned) {
    
    try {
    
    if (file != null) {
    
    file.close();
    
    }
    
    if (zip != null) {
    
    zip.close();
    
    }
    
    } catch (IOException ioe) {
    
    //ignore close exceptions
    
    }
    
    }
    
    }
    
    // Return the information we have gathered in a new object
    
    return new JavaClass(class_name_index, superclass_name_index, file_name, major, minor,
    
    access_flags, constant_pool, interfaces, fields, methods, attributes);
    
    }

  /**

  • Read information about the attributes of the class.
  • @throws IOException
  • @throws ClassFormatException */
    private final void readAttributes() throws IOException, ClassFormatException {
    int attributes_count;
    attributes_count = file.readUnsignedShort();
    attributes = new Attribute[attributes_count];
    for (int i = 0; i < attributes_count; i++) {
    attributes[i] = Attribute.readAttribute(file, constant_pool);
    }
    }
    

  /**

  • Read information about the class and its super class.
  • @throws IOException
  • @throws ClassFormatException /
    private final void readClassInfo() throws IOException, ClassFormatException {
    access_flags = file.readUnsignedShort();
    / Interfaces are implicitely abstract, the flag should be set
    • according to the JVM specification. */
      if ((access_flags & Constants.ACC_INTERFACE) != 0) {
      access_flags |= Constants.ACC_ABSTRACT;
      }
      if (((access_flags & Constants.ACC_ABSTRACT) != 0)
      && ((access_flags & Constants.ACC_FINAL) != 0)) {
      throw new ClassFormatException("Class " + file_name + " can't be both final and abstract");
      }
      class_name_index = file.readUnsignedShort();
      superclass_name_index = file.readUnsignedShort();
      }
      

  /**

  • Read constant pool entries.
  • @throws IOException
  • @throws ClassFormatException */
    private final void readConstantPool() throws IOException, ClassFormatException {
    constant_pool = new ConstantPool(file);
    }
    

  /**

  • Read information about the fields of the class, i.e., its variables.
  • @throws IOException
  • @throws ClassFormatException */
    private final void readFields() throws IOException, ClassFormatException {
    int fields_count;
    fields_count = file.readUnsignedShort();
    fields = new Field[fields_count];
    for (int i = 0; i < fields_count; i++) {
    fields[i] = new Field(file, constant_pool);
    }
    }
    

  /******************** Private utility methods **********************/
  
  /**

  • Check whether the header of the file is ok.
  • Of course, this has to be the first action on successive file reads.
  • @throws IOException
  • @throws ClassFormatException */
    private final void readID() throws IOException, ClassFormatException {
    int magic = 0xCAFEBABE;
    if (file.readInt() != magic) {
    throw new ClassFormatException(file_name + " is not a Java .class file");
    }
    }
    

  /**

  • Read information about the interfaces implemented by this class.
  • @throws IOException
  • @throws ClassFormatException */
    private final void readInterfaces() throws IOException, ClassFormatException {
    int interfaces_count;
    interfaces_count = file.readUnsignedShort();
    interfaces = new int[interfaces_count];
    for (int i = 0; i < interfaces_count; i++) {
    interfaces[i] = file.readUnsignedShort();
    }
    }
    

  /**

  • Read information about the methods of the class.
  • @throws IOException
  • @throws ClassFormatException */
    private final void readMethods() throws IOException, ClassFormatException {
    int methods_count;
    methods_count = file.readUnsignedShort();
    methods = new Method[methods_count];
    for (int i = 0; i < methods_count; i++) {
    methods[i] = new Method(file, constant_pool);
    }
    }
    

  /**

  • Read major and minor version of compiler which created the file.
  • @throws IOException
  • @throws ClassFormatException */
    private final void readVersion() throws IOException, ClassFormatException {
    minor = file.readUnsignedShort();
    major = file.readUnsignedShort();
    }
    }
    

3.问题
发现这个解析类的文件会先去判断class的头信息来确定是不是class文件，

但是由于我们对class进行了加密，所以头信息变了，所以这个解析class文件的类会报错，

也就不会调用到classloader了。

【继续】

文章有点长，不知道有人有耐心看完不。

1.上面的问题折腾了一天，才发现是自己解密的部分有问题，

2.不过也是有收获的，发现自定写的loader只能加载非class的文件，而不能加载class

3.意思就是说，你需要将原来的class文件加密并改变文件后缀，然后配合自己的loader使用

4.加密和解密两个程序：加密，解密

【delegate】

由于自己英语水平有限，所以之前的tomcat文章一知半解，

通过今天的研究发现context.xml中的delegate属性的用法。

1.loader的代码：

[java] view plaincopy在CODE上查看代码片派生到我的代码片
package com.uikoo9.loader;

import java.io.ByteArrayOutputStream;

import java.io.FileInputStream;

import java.io.IOException;

import org.apache.catalina.loader.WebappClassLoader;

/**

• 自定义的classloader
• 可以解密文件并加载

• @author uikoo9
  */
  
  public class UClassLoader extends WebappClassLoader{

  /**

  • 默认构造器 */
    public UClassLoader() {
    super();
    }
    

  /**

  • 默认构造器
  • @param parent */
    public UClassLoader(ClassLoader parent) {
    super(parent);
    }
    

  /* (non-Javadoc)

  • @see org.apache.catalina.loader.WebappClassLoader#findClass(java.lang.String)
    */
    
    public Class<?> findClass(String name) throws ClassNotFoundException {
    
    byte[] classBytes = null;
    
    try {
    
    if(name.contains("uikoo9")){
    
    System.out.println("++++++" + name);
    
    classBytes = loadClassBytesEncrypt(name);
    
    }else{
    
    System.out.println("-------" + name);
    
    classBytes = loadClassBytesDefault(name);
    
    }
    
    } catch (Exception e) {
    
    e.printStackTrace();
    
    }

    Class<?> cl = defineClass(name, classBytes, 0, classBytes.length);
    
    if (cl == null)
    
    throw new ClassNotFoundException(name);
    
    return cl;
    
    }

  @Override
  
  public Class<?> loadClass(String name) throws ClassNotFoundException {
  
  if(name.contains("uikoo9")){
  
  return findClass(name);
  
  }else{
  
  return super.loadClass(name);
  
  }
  
  }

  /**

  • 加载加密后的class字节流
  • @param name
  • @return
  • @throws IOException */
    private byte[] loadClassBytesEncrypt(String name) throws IOException {
    String cname = name.replace('.', '/') + ".uikoo9";
    FileInputStream in = null;
    in = new FileInputStream(cname);
    try {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    int ch;
    while ((ch = in.read()) != -1) {
    buffer.write((byte)(ch - 2));
    }
    in.close();
    return buffer.toByteArray();
    } finally {
    in.close();
    }
    }
    

  /**

  • 加载普通的class字节流
  • @param name
  • @return
  • @throws IOException */
    private byte[] loadClassBytesDefault(String name) throws IOException {
    String cname = name.replace('.', '/') + ".class";
    FileInputStream in = null;
    in = new FileInputStream(cname);
    try {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    int ch;
    while ((ch = in.read()) != -1) {
    buffer.write((byte)ch);
    }
    in.close();
    return buffer.toByteArray();
    } finally {
    in.close();
    }
    }
    }
    

2.delegate="false"时，启动tomcat：
[html] view plaincopy在CODE上查看代码片派生到我的代码片

3.delegate="true"时，启动tomcat：
[html] view plaincopy在CODE上查看代码片派生到我的代码片

4.总结

delegate为true的时候自定义的loader只用来加载自己的代码