[转]JAVA 反射及使用

<%@page contentType="text/html; charset=GBK"%>

<%@page import="java.security.*,java.net.*,java.io.*"%>

<%!

  public static URL getClassLocation(final Class cls) {

    if (cls == null)throw new IllegalArgumentException("null input: cls");

    URL result = null;

    final String clsAsResource = cls.getName().replace('.', '/').concat(".class");

    final ProtectionDomain pd = cls.getProtectionDomain();

    // java.lang.Class contract does not specify if 'pd' can ever be null;

    // it is not the case for Sun's implementations, but guard against null

    // just in case:

    if (pd != null) {

      final CodeSource cs = pd.getCodeSource();

      // 'cs' can be null depending on the classloader behavior:

      if (cs != null) result = cs.getLocation();

      if (result != null) {

        // Convert a code source location into a full class file location

        // for some common cases:

        if ("file".equals(result.getProtocol())) {

          try {

            if (result.toExternalForm().endsWith(".jar") ||

                result.toExternalForm().endsWith(".zip"))

              result = new URL("jar:".concat(result.toExternalForm())

                               .concat("!/").concat(clsAsResource));

            else if (new File(result.getFile()).isDirectory())

              result = new URL(result, clsAsResource);

          }

          catch (MalformedURLException ignore) {}

        }

      }

    }

    if (result == null) {

      // Try to find 'cls' definition as a resource; this is not

      // document．d to be legal, but Sun's implementations seem to         //allow this:

      final ClassLoader clsLoader = cls.getClassLoader();

      result = clsLoader != null ?

          clsLoader.getResource(clsAsResource) :

          ClassLoader.getSystemResource(clsAsResource);

    }

    return result;

  }

%>

<html>

<head>

<title>srcAdd.jar</title>

</head>

<body bgcolor="#ffffff">

  使用方法，className参数为类的全名，不需要.class后缀，如

  srcAdd.jsp?className=java.net.URL

<%

try

{

  String classLocation = null;

  String error = null;

  String className = request.getParameter("className");

  classLocation =  ""+getClassLocation(Class.forName(className));

  if (error == null) {

    out.print("类" + className + "实例的物理文件位于：");

    out.print("<hr>");

    out.print(classLocation);

  }

  else {

    out.print("类" + className + "没有对应的物理文件。<br>");

    out.print("错误：" + error);

  }

}catch(Exception e)

{

  out.print("异常。"+e.getMessage());

}

%>

</body>

</html>

srcAdd.jsp

还有一个类： ClassLocationUtils.java ，在 IDEA 断点调试时，可按 Alt+F8 组合键，弹出 Evaluate Expression 对话框，

在 Expression 处输入 ClassLocationUtils.where(<类名>.class) 即可获知当前类是从哪个 JAR 包中加载的。

package com.smart.utils;

import java.io.File;

import java.net.MalformedURLException;

import java.net.URL;

import java.security.CodeSource;

import java.security.ProtectionDomain;

/**

 * tools to find which jar does the class come from

 * @author : chenxh

 * @date: 16-04-0

 */

public class ClassLocationUtils {

    /**

     * find the location of the class come from

     * @param cls

     * @return

     */

    public static String where(final Class cls) {

        if (cls == null)throw new IllegalArgumentException("null input: cls");

        URL result = null;

        final String clsAsResource = cls.getName().replace('.', '/').concat(".class");

        final ProtectionDomain pd = cls.getProtectionDomain();

        if (pd != null) {

            final CodeSource cs = pd.getCodeSource();

            if (cs != null) result = cs.getLocation();

            if (result != null) {

                if ("file".equals(result.getProtocol())) {

                    try {

                        if (result.toExternalForm().endsWith(".jar") ||

                                result.toExternalForm().endsWith(".zip"))

                            result = new URL("jar:".concat(result.toExternalForm())

                                    .concat("!/").concat(clsAsResource));

                        else if (new File(result.getFile()).isDirectory())

                            result = new URL(result, clsAsResource);

                    }

                    catch (MalformedURLException ignore) {}

                }

            }

        }

        if (result == null) {

            final ClassLoader clsLoader = cls.getClassLoader();

            result = clsLoader != null ?

                    clsLoader.getResource(clsAsResource) :

                    ClassLoader.getSystemResource(clsAsResource);

        }

        return result.toString();

    }

}

ClassLocationUtils.java

-- 本文摘自《精通Spring 4.x 企业应用开发实战》

Constructor 类的构造函数反射类

Method 类方法的反射类 name 为方法名 Class 为方法入参类型列表

Class getReturnType() 获得方法的返回值类型

Class[] getParameterTypes() 获得方法的入参类型数组

Class[] getExceptionTypes() 获得方法的异常类型数组

Annotation[][] getParameterAnnotations() 获得方法的注解信息

Field 类的成员变量的反射类

getDeclaredFields() 获得类的成员变量反射对象数组

getDeclaredField(String name) 获得某个特定名称的成员变量反射对象

set(Object obj,Object value) 操作的目标对象赋值

... 此外，还有包 Package 的反射类

[转]JAVA 反射及使用

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[转]JAVA 反射及使用

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