手写web框架之开发一个类加载器

 ackage io.renren.common;

 import lombok.extern.slf4j.Slf4j;
 import org.apache.commons.lang3.StringUtils;

 import java.io.File;
 import java.io.FileFilter;
 import java.io.IOException;
 import java.net.JarURLConnection;
 import java.net.URL;
 import java.util.Enumeration;
 import java.util.HashSet;
 import java.util.Set;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;

 @Slf4j
 public class ClassUtil {

     /**
      * 获取类加载器
      * 获取加载器类的实现比较简单，只需获取当前线程的ClassLoader
      */
     public static ClassLoader getClassLoader() {
         return Thread.currentThread().getContextClassLoader();
     }

     /**
      * **
      * 加载类
      * 加载类需要提供类名与是否初始化的标志，这里提到的初始化指是否执行类的静态代码块;
      * 为了提高加载类的性能，可以将loadClass方法的isInitialized参数设置false
      */
     public static Class<?> loadClass(String className, boolean isInitialized) {
         Class<?> cls = null;
         try {
            cls= Class.forName(className, isInitialized, getClassLoader());
         } catch (ClassNotFoundException e) {
             log.error("load class failure.", e);
             throw new RuntimeException(e);
         }
         return cls;
     }

     /**
      * 获取指定包名下的所有类
      */
     public static Set<Class<?>> getClassSet(String packageName) {
         Set<Class<?>> classSet = new HashSet<Class<?>>();
         try {
             Enumeration<URL> urls = getClassLoader().getResources(packageName.replace(".", "/"));
             while (urls.hasMoreElements()) {
                 URL url = urls.nextElement();
                 if (url != null) {
                     String protocol = url.getProtocol();
                     if ("file".equals(protocol)) {
                         String packagePath = url.getPath().replace("%20", "");
                         addClass(classSet, packagePath, packageName);
                     } else if ("jar".equals(protocol)) {
                         JarURLConnection jarURLConnection = (JarURLConnection) url.openConnection();
                         if (jarURLConnection != null) {
                             JarFile jarFile = jarURLConnection.getJarFile();
                             if (jarFile != null) {
                                 Enumeration<JarEntry> jarEntries = jarFile.entries();
                                 while (jarEntries.hasMoreElements()) {
                                     JarEntry jarEntry = jarEntries.nextElement();
                                     String jarEntryName = jarEntry.getName();
                                     if (jarEntryName.endsWith(".class")) {
                                         String className = jarEntryName.substring(0, jarEntryName.lastIndexOf("."))
                                                 .replaceAll("/", ".");
                                         doAddClass(classSet, className);
                                     }
                                 }
                             }
                         }
                     }
                 }
             }
         } catch (IOException e) {
             log.error("get class set failure.", e);
             throw new RuntimeException(e);
         }
         return classSet;
     }

     private static void addClass(Set<Class<?>> classSet, String packagePath, String packageName) {
         File[] files = new File(packagePath).listFiles(new FileFilter() {
             public boolean accept(File file) {
                 return (file.isFile() && file.getName().endsWith(".class")) || file.isDirectory();
             }
         });
         for (File file : files) {
             String fileName = file.getName();
             if (file.isFile()) {
                 String className = fileName.substring(0, fileName.lastIndexOf("."));
                 if (StringUtils.isNotEmpty(packageName)) {
                     className = packageName + "." + className;
                 }
                 doAddClass(classSet, className);
             } else {
                 String subPackagePath = fileName;
                 if (StringUtils.isNotEmpty(packageName)) {
                     subPackagePath = packagePath + "/" + subPackagePath;
                 }
                 String subPackageName = fileName;
                 if (StringUtils.isNotEmpty(packageName)) {
                     subPackageName = packageName + "." + subPackageName;
                 }
                 addClass(classSet, subPackagePath, subPackageName);
             }
         }
     }

     private static void doAddClass(Set<Class<?>> classSet, String className) {
         Class<?> cls = loadClass(className, true);
         classSet.add(cls);
     }

实现扫描包路径下类的功能