在Java的反射中，Class.forName和ClassLoader的区别

装载：通过累的全限定名获取二进制字节流，将二进制字节流转换成方法区中的运行时数据结构，在内存中生成Java.lang.class对象； 
链接：执行下面的校验、准备和解析步骤，其中解析步骤是可以选择的； 
　　校验：检查导入类或接口的二进制数据的正确性；（文件格式验证，元数据验证，字节码验证，符号引用验证） 
　　准备：给类的静态变量分配并初始化存储空间； 
　　解析：将常量池中的符号引用转成直接引用； 
初始化：激活类的静态变量的初始化Java代码和静态Java代码块，并初始化程序员设置的变量值。

@CallerSensitive
 public static Class<?> forName(String className)
 throws ClassNotFoundException {
 Class<?> caller = Reflection.getCallerClass();
 return forName0(className, true, ClassLoader.getClassLoader(caller), caller);
 }
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/* @param name fully qualified name of the desired class
 * @param initialize if {@code true} the class will be initialized.
 * See Section 12.4 of <em>The Java Language Specification</em>.
 * @param loader class loader from which the class must be loaded
 * @return class object representing the desired class
 *
 * @exception LinkageError if the linkage fails
 * @exception ExceptionInInitializerError if the initialization provoked
 * by this method fails
 * @exception ClassNotFoundException if the class cannot be located by
 * the specified class loader
 *
 * @see java.lang.Class#forName(String)
 * @see java.lang.ClassLoader
 * @since 1.2
 */
 @CallerSensitive
 public static Class<?> forName(String name, boolean initialize,
 ClassLoader loader)
 throws ClassNotFoundException
 {
 Class<?> caller = null;
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 // Reflective call to get caller class is only needed if a security manager
 // is present. Avoid the overhead of making this call otherwise.
 caller = Reflection.getCallerClass();
 if (sun.misc.VM.isSystemDomainLoader(loader)) {
 ClassLoader ccl = ClassLoader.getClassLoader(caller);
 if (!sun.misc.VM.isSystemDomainLoader(ccl)) {
 sm.checkPermission(
 SecurityConstants.GET_CLASSLOADER_PERMISSION);
 }
 }
 }
 return forName0(name, initialize, loader, caller);
 }
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public class ClassForName {
 //静态代码块
 static {
 System.out.println("执行了静态代码块");
 }
 //静态变量
 private static String staticFiled = staticMethod();
 //赋值静态变量的静态方法
 public static String staticMethod(){
 System.out.println("执行了静态方法");
 return "给静态字段赋值了";
 }
}
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public class MyTest {
 @Test
 public void test44(){
 try {
 Class.forName("com.test.mytest.ClassForName");
 System.out.println("#########分割符(上面是Class.forName的加载过程，下面是ClassLoader的加载过程)##########");
 ClassLoader.getSystemClassLoader().loadClass("com.test.mytest.ClassForName");
 } catch (ClassNotFoundException e) {
 e.printStackTrace();
 }
 }
}
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执行了静态代码块
执行了静态方法
#########分割符(上面是Class.forName的加载过程，下面是ClassLoader的加载过程)##########
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public class Driver extends NonRegisteringDriver implements java.sql.Driver { 
 // ~ Static fields/initializers 
 // --------------------------------------------- 
 
 // 
 // Register ourselves with the DriverManager 
 // 
 static { 
 try { 
 java.sql.DriverManager.registerDriver(new Driver()); 
 } catch (SQLException E) { 
 throw new RuntimeException("Can't register driver!"); 
 } 
 } 
 
 // ~ Constructors 
 // ----------------------------------------------------------- 
 
 /** 
 * Construct a new driver and register it with DriverManager 
 * 
 * @throws SQLException 
 * if a database error occurs. 
 */ 
 public Driver() throws SQLException { 
 // Required for Class.forName().newInstance() 
 } 
}
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