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