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tomcat 7 源码分析-2 类加载ClassLoader

TomcatApacheJ#thread 
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tomcat 7 源码分析-2 类加载ClassLoader

 

tomcat在启动的时候使用了三个类加载器

 

Java代码  收藏代码
  1. private   void  initClassLoaders() {  
  2.     try  {  
  3.         commonLoader = createClassLoader("common" ,  null );  
  4.         if ( commonLoader ==  null  ) {  
  5.             // no config file, default to this loader - we might be in a 'single' env.   
  6.             commonLoader=this .getClass().getClassLoader();  
  7.         }  
  8.         catalinaLoader = createClassLoader("server" , commonLoader);  
  9.         sharedLoader = createClassLoader("shared" , commonLoader);  
  10.     } catch  (Throwable t) {  
  11.         log.error("Class loader creation threw exception" , t);  
  12.         System.exit(1 );  
  13.     }  
  14. }   
    private void initClassLoaders() {
        try {
            commonLoader = createClassLoader("common", null);
            if( commonLoader == null ) {
                // no config file, default to this loader - we might be in a 'single' env.
                commonLoader=this.getClass().getClassLoader();
            }
            catalinaLoader = createClassLoader("server", commonLoader);
            sharedLoader = createClassLoader("shared", commonLoader);
        } catch (Throwable t) {
            log.error("Class loader creation threw exception", t);
            System.exit(1);
        }
    }

 三个类加载器加载了catalina.properties中的jar

 

Java代码  收藏代码
  1. common.loader=${catalina.base}/lib,${catalina.base}/lib/*.jar,${catalina.home}/lib,${catalina.home}/lib/*.jar  
  2. server.loader=  
  3. shared.loader=   
common.loader=${catalina.base}/lib,${catalina.base}/lib/*.jar,${catalina.home}/lib,${catalina.home}/lib/*.jar
server.loader=
shared.loader=

 由此可见三个类加载器加载的jar是一样的。为什么要用三个类加载器，从名称看应该是有分别的作用考虑，负载的考虑也许吧。

此外    private ClassLoader createClassLoader(String name, ClassLoader parent)中调用        ClassLoader classLoader = ClassLoaderFactory.createClassLoader

            (locations, types, parent);

tomcat自定义了一个类加载器，并且定义了ClassLoaderFactory根据参数定义返回classloader。总体上ClassLoaderFactory就是根据catalina.properties中的jar的位置，做了一些字符串的处理。

 

Java代码  收藏代码
  1. public   static  ClassLoader createClassLoader(String locations[],  
  2.                                                 Integer types[],  
  3.                                                 ClassLoader parent)  
  4.         throws  Exception {  
  5.   
  6.         if  (log.isDebugEnabled())  
  7.             log.debug("Creating new class loader" );  
  8.   
  9.         // Construct the "class path" for this class loader   
  10.         Set<URL> set = new  LinkedHashSet<URL>();  
  11.   
  12.         if  (locations !=  null  && types !=  null  && locations.length == types.length) {  
  13.             for  ( int  i =  0 ; i < locations.length; i++)  {  
  14.                 String location = locations[i];  
  15.                 if  ( types[i] == IS_URL ) {  
  16.                     URL url = new  URL(location);  
  17.                     if  (log.isDebugEnabled())  
  18.                         log.debug("  Including URL "  + url);  
  19.                     set.add(url);  
  20.                 } else   if  ( types[i] == IS_DIR ) {  
  21.                     File directory = new  File(location);  
  22.                     directory = new  File(directory.getCanonicalPath());  
  23.                     if  (!directory.exists() || !directory.isDirectory() ||  
  24.                         !directory.canRead())  
  25.                          continue ;  
  26.                     URL url = directory.toURI().toURL();  
  27.                     if  (log.isDebugEnabled())  
  28.                         log.debug("  Including directory "  + url);  
  29.                     set.add(url);  
  30.                 } else   if  ( types[i] == IS_JAR ) {  
  31.                     File file=new  File(location);  
  32.                     file = new  File(file.getCanonicalPath());  
  33.                     if  (!file.exists() || !file.canRead())  
  34.                         continue ;  
  35.                     URL url = file.toURI().toURL();  
  36.                     if  (log.isDebugEnabled())  
  37.                         log.debug("  Including jar file "  + url);  
  38.                     set.add(url);  
  39.                 } else   if  ( types[i] == IS_GLOB ) {  
  40.                     File directory=new  File(location);  
  41.                     if  (!directory.exists() || !directory.isDirectory() ||  
  42.                         !directory.canRead())  
  43.                         continue ;  
  44.                     if  (log.isDebugEnabled())  
  45.                         log.debug("  Including directory glob "   
  46.                             + directory.getAbsolutePath());  
  47.                     String filenames[] = directory.list();  
  48.                     for  ( int  j =  0 ; j < filenames.length; j++) {  
  49.                         String filename = filenames[j].toLowerCase(Locale.ENGLISH);  
  50.                         if  (!filename.endsWith( ".jar" ))  
  51.                             continue ;  
  52.                         File file = new  File(directory, filenames[j]);  
  53.                         file = new  File(file.getCanonicalPath());  
  54.                         if  (!file.exists() || !file.canRead())  
  55.                             continue ;  
  56.                         if  (log.isDebugEnabled())  
  57.                             log.debug("    Including glob jar file "   
  58.                                 + file.getAbsolutePath());  
  59.                         URL url = file.toURI().toURL();  
  60.                         set.add(url);  
  61.                     }  
  62.                 }  
  63.             }  
  64.         }  
  65.   
  66.         // Construct the class loader itself   
  67.         URL[] array = set.toArray(new  URL[set.size()]);  
  68.         if  (log.isDebugEnabled())  
  69.             for  ( int  i =  0 ; i < array.length; i++) {  
  70.                 log.debug("  location "  + i +  " is "  + array[i]);  
  71.             }  
  72.         StandardClassLoader classLoader = null ;  
  73.         if  (parent ==  null )  
  74.             classLoader = new  StandardClassLoader(array);  
  75.         else   
  76.             classLoader = new  StandardClassLoader(array, parent);  
  77.         return  (classLoader);  
  78.   
  79.     }   
public static ClassLoader createClassLoader(String locations[],
                                                Integer types[],
                                                ClassLoader parent)
        throws Exception {

        if (log.isDebugEnabled())
            log.debug("Creating new class loader");

        // Construct the "class path" for this class loader
        Set<URL> set = new LinkedHashSet<URL>();

        if (locations != null && types != null && locations.length == types.length) {
            for (int i = 0; i < locations.length; i++)  {
                String location = locations[i];
                if ( types[i] == IS_URL ) {
                    URL url = new URL(location);
                    if (log.isDebugEnabled())
                        log.debug("  Including URL " + url);
                    set.add(url);
                } else if ( types[i] == IS_DIR ) {
                    File directory = new File(location);
                    directory = new File(directory.getCanonicalPath());
                    if (!directory.exists() || !directory.isDirectory() ||
                        !directory.canRead())
                         continue;
                    URL url = directory.toURI().toURL();
                    if (log.isDebugEnabled())
                        log.debug("  Including directory " + url);
                    set.add(url);
                } else if ( types[i] == IS_JAR ) {
                    File file=new File(location);
                    file = new File(file.getCanonicalPath());
                    if (!file.exists() || !file.canRead())
                        continue;
                    URL url = file.toURI().toURL();
                    if (log.isDebugEnabled())
                        log.debug("  Including jar file " + url);
                    set.add(url);
                } else if ( types[i] == IS_GLOB ) {
                    File directory=new File(location);
                    if (!directory.exists() || !directory.isDirectory() ||
                        !directory.canRead())
                        continue;
                    if (log.isDebugEnabled())
                        log.debug("  Including directory glob "
                            + directory.getAbsolutePath());
                    String filenames[] = directory.list();
                    for (int j = 0; j < filenames.length; j++) {
                        String filename = filenames[j].toLowerCase(Locale.ENGLISH);
                        if (!filename.endsWith(".jar"))
                            continue;
                        File file = new File(directory, filenames[j]);
                        file = new File(file.getCanonicalPath());
                        if (!file.exists() || !file.canRead())
                            continue;
                        if (log.isDebugEnabled())
                            log.debug("    Including glob jar file "
                                + file.getAbsolutePath());
                        URL url = file.toURI().toURL();
                        set.add(url);
                    }
                }
            }
        }

        // Construct the class loader itself
        URL[] array = set.toArray(new URL[set.size()]);
        if (log.isDebugEnabled())
            for (int i = 0; i < array.length; i++) {
                log.debug("  location " + i + " is " + array[i]);
            }
        StandardClassLoader classLoader = null;
        if (parent == null)
            classLoader = new StandardClassLoader(array);
        else
            classLoader = new StandardClassLoader(array, parent);
        return (classLoader);

    }

 定义了类加载器后，在init()中加载

 

Java代码  收藏代码
  1. Class<?> startupClass =  
  2.     catalinaLoader.loadClass  
  3.     ("org.apache.catalina.startup.Catalina" );   
        Class<?> startupClass =
            catalinaLoader.loadClass
            ("org.apache.catalina.startup.Catalina");

 这个才是tomcat的守护进程。

 

Java代码  收藏代码
  1. Thread.currentThread().setContextClassLoader(catalinaLoader);  
  2.   
  3.  SecurityClassLoad.securityClassLoad(catalinaLoader);  
  4.   
  5.  // Load our startup class and call its process() method   
  6.  if  (log.isDebugEnabled())  
  7.      log.debug("Loading startup class" );  
  8.  Class<?> startupClass =  
  9.      catalinaLoader.loadClass  
  10.      ("org.apache.catalina.startup.Catalina" );  
  11.  Object startupInstance = startupClass.newInstance();          
  12.  // Set the shared extensions class loader   
  13.  if  (log.isDebugEnabled())  
  14.      log.debug("Setting startup class properties" );  
  15.  String methodName = "setParentClassLoader" ;  
  16.  Class<?> paramTypes[] = new  Class[ 1 ];  
  17.  paramTypes[0 ] = Class.forName( "java.lang.ClassLoader" );  
  18.  Object paramValues[] = new  Object[ 1 ];  
  19.  paramValues[0 ] = sharedLoader;  
  20.  Method method =  
  21.      startupInstance.getClass().getMethod(methodName, paramTypes);  
  22.  method.invoke(startupInstance, paramValues);  
  23.  catalinaDaemon = startupInstance;   
       Thread.currentThread().setContextClassLoader(catalinaLoader);

        SecurityClassLoad.securityClassLoad(catalinaLoader);

        // Load our startup class and call its process() method
        if (log.isDebugEnabled())
            log.debug("Loading startup class");
        Class<?> startupClass =
            catalinaLoader.loadClass
            ("org.apache.catalina.startup.Catalina");
        Object startupInstance = startupClass.newInstance();        
        // Set the shared extensions class loader
        if (log.isDebugEnabled())
            log.debug("Setting startup class properties");
        String methodName = "setParentClassLoader";
        Class<?> paramTypes[] = new Class[1];
        paramTypes[0] = Class.forName("java.lang.ClassLoader");
        Object paramValues[] = new Object[1];
        paramValues[0] = sharedLoader;
        Method method =
            startupInstance.getClass().getMethod(methodName, paramTypes);
        method.invoke(startupInstance, paramValues);
        catalinaDaemon = startupInstance;

 这里要说的是

 

Class.forName()和ClassLoader.loadClass()的区别？

这两个方法由给类名作为参数，动态的定位并且加载类。然而，两者行为的区别在于用哪个加载器(java.lang.ClassLoader)去加载和加载完后的类是否就已经初始化。

对于Class.forName()最常见的形式就是用一个单独的String为参数，使用当前调用者的类加载器。这个类加载器加载代码执行 forName()方法。比较ClassLoader.loadClass()，它是一个实例方法，需要你去选择确定的classloader。这个类加 载器可以是也可以不是当前加载器。如果选择一个特定的类加载器对你的设计尤为重要，你可以使用ClassLoader.loadClass()或者三个参 数的forName()。

更进一步，Class.forName()的常见形式会初始化加载的类。这样做的就是执行了类的静态初始化方法，也就是byte代码对应的所有静态 初始化表达式。这和ClassLoader.loadClass()是不同的，ClassLoader.loadClass()直到类第一次使用的时候才 初始化。

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