004 关于Java如何扫描指定package下所有的类

q前言：

　　在工作中看到这个知识点，就顺便参考了百度的一些资料，整理一下，希望以后用的到。

一：理论部分

1.使用场景

　　写一个MVC框架，需要从包中扫描出组件并注册到容器中，而JDK没有提供现成的从方法，只能自己实现

2.需求

　　给定一个包名，编程得到该包(和其所有子包)下所有的类文件

3.思路

　　有的web server在部署运行时会解压jar包，因此class文件会在普通的文件目录下。

　　如果web server不解压jar包，则class文件会直接存在于Jar包中。

　　对于前者，只需定位到class文件所在目录，然后将class文件名读取出即可；

　　对于后者，则需先定位到jar包所在目录，然后使用JarInputStream读取Jar包，得到class类名。

二：程序实现

1.程序目录

　　

2.ClasspathPackageScanner.java

 package com.scan;

 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.jar.JarEntry;
 import java.util.jar.JarInputStream;

 public class ClasspathPackageScanner implements PackageScanner{
     private Logger logger = LoggerFactory.getLogger(ClasspathPackageScanner.class);
     private String basePackage;
     private ClassLoader cl;

     /**
      * 初始化
      * @param basePackage
      */
     public ClasspathPackageScanner(String basePackage) {
         this.basePackage = basePackage;
         this.cl = getClass().getClassLoader();
     }
     public ClasspathPackageScanner(String basePackage, ClassLoader cl) {
         this.basePackage = basePackage;
         this.cl = cl;
     }
     /**
      *获取指定包下的所有字节码文件的全类名
      */
     public List<String> getFullyQualifiedClassNameList() throws IOException {
         logger.info("开始扫描包{}下的所有类", basePackage);
         return doScan(basePackage, new ArrayList<String>());
     }

     /**
      *doScan函数
      * @param basePackage
      * @param nameList
      * @return
      * @throws IOException
      */
     private List<String> doScan(String basePackage, List<String> nameList) throws IOException {
         String splashPath = StringUtil.dotToSplash(basePackage);
         URL url = cl.getResource(splashPath);   //file:/D:/WorkSpace/java/ScanTest/target/classes/com/scan
         String filePath = StringUtil.getRootPath(url);
         List<String> names = null; // contains the name of the class file. e.g., Apple.class will be stored as "Apple"
         if (isJarFile(filePath)) {// 先判断是否是jar包，如果是jar包，通过JarInputStream产生的JarEntity去递归查询所有类
             if (logger.isDebugEnabled()) {
                 logger.debug("{} 是一个JAR包", filePath);
             }
             names = readFromJarFile(filePath, splashPath);
         } else {
             if (logger.isDebugEnabled()) {
                 logger.debug("{} 是一个目录", filePath);
             }
             names = readFromDirectory(filePath);
         }
         for (String name : names) {
             if (isClassFile(name)) {
                 nameList.add(toFullyQualifiedName(name, basePackage));
             } else {
                 doScan(basePackage + "." + name, nameList);
             }
         }
         if (logger.isDebugEnabled()) {
             for (String n : nameList) {
                 logger.debug("找到{}", n);
             }
         }
         return nameList;
     }

     private String toFullyQualifiedName(String shortName, String basePackage) {
         StringBuilder sb = new StringBuilder(basePackage);
         sb.append('.');
         sb.append(StringUtil.trimExtension(shortName));
         //打印出结果
         System.out.println(sb.toString());
         return sb.toString();
     }

     private List<String> readFromJarFile(String jarPath, String splashedPackageName) throws IOException {
         if (logger.isDebugEnabled()) {
             logger.debug("从JAR包中读取类: {}", jarPath);
         }
         JarInputStream jarIn = new JarInputStream(new FileInputStream(jarPath));
         JarEntry entry = jarIn.getNextJarEntry();
         List<String> nameList = new ArrayList<String>();
         while (null != entry) {
             String name = entry.getName();
             if (name.startsWith(splashedPackageName) && isClassFile(name)) {
                 nameList.add(name);
             }

             entry = jarIn.getNextJarEntry();
         }

         return nameList;
     }

     private List<String> readFromDirectory(String path) {
         File file = new File(path);
         String[] names = file.list();

         if (null == names) {
             return null;
         }

         return Arrays.asList(names);
     }

     private boolean isClassFile(String name) {
         return name.endsWith(".class");
     }

     private boolean isJarFile(String name) {
         return name.endsWith(".jar");
     }

     /**
      * For test purpose.
      */
     public static void main(String[] args) throws Exception {
         PackageScanner scan = new ClasspathPackageScanner("com.scan");
         scan.getFullyQualifiedClassNameList();
     }
 }

3.PackageScanner接口

 package com.scan;
 import java.io.IOException;
 import java.util.List;
 public interface PackageScanner {
     public List<String> getFullyQualifiedClassNameList() throws IOException;
 }

4.StringUtil.java

 package com.scan;

 import java.net.URL;

 public class StringUtil {
     private StringUtil() {

     }
     /**
      * "file:/home/whf/cn/fh" -> "/home/whf/cn/fh"
      * "jar:file:/home/whf/foo.jar!cn/fh" -> "/home/whf/foo.jar"
      */
     public static String getRootPath(URL url) {
         String fileUrl = url.getFile();
         int pos = fileUrl.indexOf('!');

         if (-1 == pos) {
             return fileUrl;
         }

         return fileUrl.substring(5, pos);
     }

     /**
      * "cn.fh.lightning" -> "cn/fh/lightning"
      * @param name
      * @return
      */
     public static String dotToSplash(String name) {
         return name.replaceAll("\\.", "/");
     }

     /**
      * "Apple.class" -> "Apple"
      */
     public static String trimExtension(String name) {
         int pos = name.indexOf('.');
         if (-1 != pos) {
             return name.substring(0, pos);
         }

         return name;
     }

     /**
      * /application/home -> /home
      * @param uri
      * @return
      */
     public static String trimURI(String uri) {
         String trimmed = uri.substring(1);
         int splashIndex = trimmed.indexOf('/');

         return trimmed.substring(splashIndex);
     }
 }

5.结果