springboot 如何扫描程序中带有指定注解的类和方法

使用springboot的人基本都知道swagger，那么swagger是如何生成swagger-ui.html页面的呢？相信大家都能猜到，就是扫描程序中带有指定注解的类(带有@RestController和 @Controller)和方法(@RequestMapping等)，然后又根据方法上的@ApiOperation和@ApiImplicitParams去生成页面上要显示的一些元素。
实际项目中我们也会有类似需求，例如权限校验，我们需要先扫描程序中有哪些接口(就是找有哪些类有@RestController注解)，然后在根据自定义的一些注解，扫描是否这些controller的方法需要配置权限校验。那么如何来实现？

第一步，

根据basePackage，开始遍历所有的类，然后测试该类是否添加了@RestController注解。
需要注意的是，当我们的类是在jar文件中时，不需要递归，但是在普通的文件中(目录存放文件)需要递归循环。

private List<Class<?>> getClassesWithAnnotationFromPackage(String packageName, Class<? extends Annotation> annotation) {
        List<Class<?>> classList = new ArrayList<Class<?>>();
        String packageDirName = packageName.replace('.', '/');
        Enumeration<URL> dirs = null;

        try {
            dirs = Thread.currentThread().getContextClassLoader().getResources(packageDirName);
        }
        catch (IOException e) {
            log.error("Failed to get resource", e);
            return null;
        }

        while (dirs.hasMoreElements()) {
            URL url = dirs.nextElement();//file:/D:/E/workspaceGitub/springboot/JSONDemo/target/classes/com/yq/controller
            String protocol = url.getProtocol();//file

            //https://docs.oracle.com/javase/7/docs/api/java/net/URL.html
            //http, https, ftp, file, and jar
            //本文只需要处理file和jar
            if ("file".equals(protocol) ) {
                String filePath = null;
                try {
                    filePath = URLDecoder.decode(url.getFile(), "UTF-8");///D:/E/workspaceGitub/springboot/JSONDemo/target/classes/com/yq/controller
                }
                catch (UnsupportedEncodingException e) {
                    log.error("Failed to decode class file", e);
                }

                filePath = filePath.substring(1);
                getClassesWithAnnotationFromFilePath(packageName, filePath, classList, annotation);
            } else if ("jar".equals(protocol)) {
                JarFile jar = null;
                try {
                    jar = ((JarURLConnection) url.openConnection()).getJarFile();
                    //扫描jar包文件 并添加到集合中
                }
                catch (Exception e) {
                    log.error("Failed to decode class jar", e);
                }

                List<Class<?>> alClassList = new ArrayList<Class<?>>();
                findClassesByJar(packageName, jar, alClassList);
                getClassesWithAnnotationFromAllClasses(alClassList, annotation, classList);
            }
            else {
                log.warn("can't process the protocol={}", protocol);
            }
        }

        return classList;
    }

private static void findClassesByJar(String pkgName, JarFile jar, List<Class<?>> classes) {
        String pkgDir = pkgName.replace(".", "/");
        Enumeration<JarEntry> entry = jar.entries();

        while (entry.hasMoreElements()) {
            // 获取jar里的一个实体 可以是目录 和一些jar包里的其他文件 如META-INF等文
            JarEntry jarEntry = entry.nextElement();
            String name = jarEntry.getName();
            // 如果是以/开头的
            if (name.charAt(0) == '/') {
                // 获取后面的字符串
                name = name.substring(1);
            }

            if (jarEntry.isDirectory() || !name.startsWith(pkgDir) || !name.endsWith(".class")) {
                continue;
            }
            //如果是一个.class文件 而且不是目录
            // 去掉后面的".class" 获取真正的类名
            String className = name.substring(0, name.length() - 6);
            Class<?> tempClass = loadClass(className.replace("/", "."));
            // 添加到集合中去
            if (tempClass != null) {
                classes.add(tempClass);
            }
        }
    }

    /**
     * 加载类
     * @param fullClsName 类全名
     * @return
     */
    private static Class<?> loadClass(String fullClsName ) {
        try {
            return Thread.currentThread().getContextClassLoader().loadClass(fullClsName );
        } catch (ClassNotFoundException e) {
            log.error("PkgClsPath loadClass", e);
        }
        return null;
    }


    //filePath is like this 'D:/E/workspaceGitub/springboot/JSONDemo/target/classes/com/yq/controller'
    private void getClassesWithAnnotationFromFilePath(String packageName, String filePath, List<Class<?>> classList,
                                           Class<? extends Annotation> annotation) {
        Path dir = Paths.get(filePath);//D:\E\workspaceGitub\springboot\JSONDemo\target\classes\com\yq\controller

        try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
            for(Path path : stream) {
                String fileName = String.valueOf(path.getFileName()); // for current dir , it is 'helloworld'
                //如果path是目录的话， 此处需要递归，
                boolean isDir = Files.isDirectory(path);
                if(isDir) {
                    getClassesWithAnnotationFromFilePath(packageName + "." + fileName , path.toString(), classList, annotation);
                }
                else  {
                    String className = fileName.substring(0, fileName.length() - 6);

                    Class<?> classes = null;
                    String fullClassPath = packageName + "." + className;
                    try {
                        log.info("fullClassPath={}", fullClassPath);
                        classes = Thread.currentThread().getContextClassLoader().loadClass(fullClassPath);
                    }
                    catch (ClassNotFoundException e) {
                        log.error("Failed to find class={}", fullClassPath, e);
                    }

                    if (null != classes && null != classes.getAnnotation(annotation)) {
                        classList.add(classes);
                    }
                }
            }
        }
        catch (IOException e) {
            log.error("Failed to read class file", e);
        }
    }

    private void getClassesWithAnnotationFromAllClasses(List<Class<?>> inClassList,
                                                      Class<? extends Annotation> annotation, List<Class<?>> outClassList) {
        for(Class<?> myClasss : inClassList) {
            if (null != myClasss && null != myClasss.getAnnotation(annotation)) {
                outClassList.add(myClasss);
            }
        }
    }

第二步

根据第一步提供的controller，遍历该类的所有方法，检查该方法是否添加MyChecker注解(MyChecker为自定义的注解)

 private void geMethodWithAnnotationFromFilePath(String fullClassPath, Map<String, String> checkIdMethodMap,
                                                             Class<? extends Annotation> methodAnnotation) {
        Class<?> classes = null;
        try {
            log.info("fullClassPath={}", fullClassPath);
            classes = Thread.currentThread().getContextClassLoader().loadClass(fullClassPath);

            Method[] methods = classes.getDeclaredMethods();

            for (Method method : methods) {
                MyChecker myAnnotation = method.getAnnotation(MyChecker.class);
                if (null != myAnnotation) {
                    checkIdMethodMap.put (myAnnotation.id(), method.getName() );
                }
            }
        }
        catch (ClassNotFoundException e) {
            log.error("Failed to find class={}", fullClassPath, e);
        }

效果截图

http://dl2.iteye.com/upload/attachment/0132/0836/2c30583b-ee70-368b-b4b7-3cb38e5b1dba.png