前言

之前写过一篇文章聊聊如何实现热插拔AOP,今天我们继续整一个类似的话题，聊聊如何实现spring拦截器的动态加载

实现核心思路

groovy热加载java + 事件监听变更拦截器

实现步骤

1、在项目的pom引入groovy GAV

 <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy</artifactId>
        </dependency>

2、编写groovy编译插件

public class GroovyCompiler implements DynamicCodeCompiler {

    private static final Logger LOG = LoggerFactory.getLogger(GroovyCompiler.class);

    /**
     * Compiles Groovy code and returns the Class of the compiles code.
     *
     */
    @Override
    public Class<?> compile(String sCode, String sName) {
        GroovyClassLoader loader = getGroovyClassLoader();
        LOG.info("Compiling filter: " + sName);
        Class<?> groovyClass = loader.parseClass(sCode, sName);
        return groovyClass;
    }

    /**
     * @return a new GroovyClassLoader
     */
    GroovyClassLoader getGroovyClassLoader() {
        return new GroovyClassLoader();
    }

    /**
     * Compiles groovy class from a file
     *
     */
    @Override
    public Class<?> compile(File file) throws IOException {
        GroovyClassLoader loader = getGroovyClassLoader();
        Class<?> groovyClass = loader.parseClass(file);
        return groovyClass;
    }
}

3、编写groovy加载java类

@Slf4j
public final class SpringGroovyLoader<T> implements GroovyLoader<T>, ApplicationContextAware {

    private final  ConcurrentMap<String, Long> groovyClassLastModified = new ConcurrentHashMap<>();

    private final DynamicCodeCompiler compiler;

    private final DefaultListableBeanFactory beanFactory;

    private ApplicationContext applicationContext;

    public SpringGroovyLoader(DynamicCodeCompiler compiler, DefaultListableBeanFactory beanFactory) {
        this.compiler = compiler;
        this.beanFactory = beanFactory;
    }

    @Override
    public boolean putObject(File file) {
        try {
            removeCurBeanIfFileChange(file);
            return registerGroovyBean(file);
        } catch (Exception e) {
            log.error(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Error loading object! Continuing. file=" + file, e);
        }

        return false;
    }

    private void removeCurBeanIfFileChange(File file) {
        String sName = file.getAbsolutePath();
        if (groovyClassLastModified.get(sName) != null
                && (file.lastModified() != groovyClassLastModified.get(sName))) {
            log.info(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> Reloading object " + sName);
            if(beanFactory.containsBean(sName)){
                beanFactory.removeBeanDefinition(sName);
                beanFactory.destroySingleton(sName);
            }
        }
    }

    private boolean registerGroovyBean(File file) throws Exception {
        String sName = file.getAbsolutePath();
        boolean containsBean = beanFactory.containsBean(sName);
        if(!containsBean){
            Class<?> clazz = compiler.compile(file);
            if (!Modifier.isAbstract(clazz.getModifiers())) {
                return registerBean(sName,clazz, file.lastModified());
            }
        }
        return false;
    }

    private boolean registerBean(String beanName, Class beanClz,long lastModified) {
        try {
            BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
            AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();
            beanDefinition.setBeanClass(beanClz);
            beanDefinition.setSource("groovyCompile");
            beanFactory.registerBeanDefinition(beanName,beanDefinition);
            BeanNameGenerator beanNameGenerator = new AnnotationBeanNameGenerator();
            String aliasBeanName = beanNameGenerator.generateBeanName(beanDefinition, beanFactory);
            beanFactory.registerAlias(beanName,aliasBeanName);
            groovyClassLastModified.put(beanName, lastModified);

            GroovyBeanRegisterEvent groovyBeanRegisterEvent = GroovyBeanRegisterEvent.builder()
                            .beanClz(beanClz).beanName(beanName).aliasBeanName(aliasBeanName).build();
            applicationContext.publishEvent(groovyBeanRegisterEvent);
            return true;
        } catch (BeanDefinitionStoreException e) {
           log.error(">>>>>>>>>>>>>>>>>>>>>>registerBean fail,cause:" + e.getMessage(),e);
        }
        return false;
    }



    @Override
    public List<T> putObjectsForClasses(String[] classNames) throws Exception {
        List<T> newObjects = new ArrayList<>();
        for (String className : classNames) {
            newObjects.add(putObjectForClassName(className));
        }
        return Collections.unmodifiableList(newObjects);
    }

    @Override
    public T putObjectForClassName(String className) throws Exception {
        Class<?> clazz = Class.forName(className);
        registerBean(className, clazz, System.currentTimeMillis());
        return (T) beanFactory.getBean(className);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

4、编写管理groovy文件变化的类

public class GroovyFileMonitorManager<T> {

    private static final Logger LOG = LoggerFactory.getLogger(GroovyFileMonitorManager.class);


    private final GroovyLoader<T> groovyLoader;
    private final GroovyProperties groovyProperties;

    public GroovyFileMonitorManager(GroovyProperties groovyProperties, GroovyLoader<T> groovyLoader) {
        this.groovyLoader = groovyLoader;
        this.groovyProperties = groovyProperties;
    }

    /**
     * Initialized the GroovyFileManager.
     *
     * @throws Exception
     */
    public void init() throws Exception {
        long startTime = System.currentTimeMillis();
        manageFiles();
        directoryChangeMonitor();
        LOG.info("Finished loading all classes. Duration = " + (System.currentTimeMillis() - startTime) + " ms.");
    }


    /**
     * Returns the directory File for a path. A Runtime Exception is thrown if the directory is in valid
     *
     * @param sPath
     * @return a File representing the directory path
     */
    public File getDirectory(String sPath) {
       return DirectoryUtil.getDirectory(sPath);
    }


    /**
     * Returns a List<File> of all Files from all polled directories
     *
     * @return
     */
    public List<File> getFiles() {
        List<File> list = new ArrayList<File>();
        if(groovyProperties.getDirectories() == null && groovyProperties.getDirectories().length == 0){
            return list;
        }
        for (String sDirectory : groovyProperties.getDirectories()) {
            if (sDirectory != null) {
                File directory = getDirectory(sDirectory);
                File[] aFiles = directory.listFiles(groovyProperties.getFilenameFilter());
                if (aFiles != null) {
                    list.addAll(Arrays.asList(aFiles));
                }
            }
        }
        return list;
    }

    @SneakyThrows
    void directoryChangeMonitor(){
          for (String sDirectory : groovyProperties.getDirectories()) {
            File directory = getDirectory(sDirectory);
            //创建文件观察器
            FileAlterationObserver observer = new FileAlterationObserver(
                    directory, FileFilterUtils.and(
                    FileFilterUtils.fileFileFilter(),
                    FileFilterUtils.suffixFileFilter(".groovy")));
            //轮询间隔时间
            long interval = TimeUnit.SECONDS.toSeconds(groovyProperties.getPollingIntervalSeconds());
            //创建文件观察器
            observer.addListener(new GroovyFileAlterationListener(this));
            //创建文件变化监听器
            FileAlterationMonitor monitor = new FileAlterationMonitor(interval, observer);
            //开始监听
            monitor.start();
        }
    }


    public void manageFiles() {
        List<File> aFiles = getFiles();
        for (File file : aFiles) {
            try {
                groovyLoader.putObject(file);
            }
            catch(Exception e) {
                LOG.error("Error init loading groovy files from disk by sync! file = " + file, e);
            }
        }

    }


    public GroovyLoader<T> getGroovyLoader() {
        return groovyLoader;
    }

    public GroovyProperties getGroovyProperties() {
        return groovyProperties;
    }
}

5、编写事件监听，变更处理拦截器

注： 核心点是利用MappedInterceptor bean能被AbstractHandlerMapping自动探测

@Component
public class InterceptorRegisterListener  {

    @Autowired
    private RequestMappingHandlerMapping requestMappingHandlerMapping;

    @Autowired
    private DefaultListableBeanFactory defaultListableBeanFactory;

    @EventListener
    public void listener(GroovyBeanRegisterEvent event){
   
        if(BaseMappedInterceptor.class.isAssignableFrom(event.getBeanClz())){
            BaseMappedInterceptor interceptor = (BaseMappedInterceptor) defaultListableBeanFactory.getBean(event.getBeanName());
            MappedInterceptor mappedInterceptor = build(interceptor);
            registerInterceptor(mappedInterceptor,event.getAliasBeanName() + "_mappedInterceptor");
        }


    }


    public MappedInterceptor build(BaseMappedInterceptor interceptor){
        return new MappedInterceptor(interceptor.getIncludePatterns(),interceptor.getExcludePatterns(),interceptor);
    }

    /**
     * @see org.springframework.web.servlet.handler.AbstractHandlerMapping#initApplicationContext()
     * @See org.springframework.web.servlet.handler.AbstractHandlerMapping#detectMappedInterceptors(java.util.List)
     * @param mappedInterceptor
     * @param beanName
     */
    @SneakyThrows
    public void registerInterceptor(MappedInterceptor mappedInterceptor, String beanName){
        if(defaultListableBeanFactory.containsBean(beanName)){
            unRegisterInterceptor(beanName);
            defaultListableBeanFactory.destroySingleton(beanName);
        }
        //将mappedInterceptor先注册成bean，利用AbstractHandlerMapping#detectMappedInterceptors从spring容器
        //自动检测Interceptor,并加入到当前的拦截器集合中
        defaultListableBeanFactory.registerSingleton(beanName,mappedInterceptor);
        Method method = AbstractHandlerMapping.class.getDeclaredMethod("initApplicationContext");
        method.setAccessible(true);
        method.invoke(requestMappingHandlerMapping);
    }

    @SneakyThrows
    public void unRegisterInterceptor(String beanName){
        MappedInterceptor mappedInterceptor = defaultListableBeanFactory.getBean(beanName,MappedInterceptor.class);
        Field field = AbstractHandlerMapping.class.getDeclaredField("adaptedInterceptors");
        field.setAccessible(true);
        List<HandlerInterceptor> handlerInterceptors = (List<HandlerInterceptor>) field.get(requestMappingHandlerMapping);
        handlerInterceptors.remove(mappedInterceptor);

    }



}

示例验证

1、编写测试服务类

public class HelloServiceImpl implements HelloService {
    @Override
    public String say(String username) {
        println ("hello:" + username)
        return "hello:" + username;
    }
}

2、编写测试控制器

@RestController
@RequestMapping("hello")
@RequiredArgsConstructor
public class HelloController {

    private final ApplicationContext applicationContext;

    @GetMapping("{username}")
    public String sayHello(@PathVariable("username")String username){
        HelloService helloService = applicationContext.getBean(HelloService.class);
        return helloService.say(username);
    }
}

浏览器访问http://localhost:8080/hello/lisi。观察控制台打印

3、在classpath目录下新增/META-INF/groovydir文件夹，并在底下放一个拦截器

@Component
public class HelloHandlerInterceptor extends BaseMappedInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("uri:" + request.getRequestURI());
       return true;

    }

    @Override
    public String[] getIncludePatterns() {
        return ["/**"];
    }

    @Override
    public String[] getExcludePatterns() {
        return new String[0];
    }
}

注： 原来的spring拦截器是没getIncludePatterns()和getExcludePatterns() ，这边是对原有拦截器稍微做了一下扩展

添加后，观察控制台

此时再次访问http://localhost:8080/hello/lisi，并观察控制台

会发现拦截器生效。接着我们将拦截器的拦截路径由/**调整成如下

Component
public class HelloHandlerInterceptor extends BaseMappedInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("uri:" + request.getRequestURI());
       return true;

    }

    @Override
    public String[] getIncludePatterns() {
        return ["/test"];
    }

    @Override
    public String[] getExcludePatterns() {
        return new String[0];
    }
}

观察控制台，会发现有如下内容输出

此时再访问http://localhost:8080/hello/lisi，观察控制台

此时说明拦截器已经发生变更

总结

动态变更java的方式有很多种，比如利用ASM、ByteBuddy等操作java字节码来实现java变更，而本文则是采用groovy脚本来变更，主要是因为groovy的学习门槛很低，只要会java基本上等于会groovy。对groovy感兴趣的同学可以通过如下链接进行学习
https://www.w3cschool.cn/groovy/

不过在使用groovy时，要特别注意因为groovy每次都是新创建class，如果没注意很容易出现OOM，其次因为groovy比较易用，很容易被拿来做成攻击的脚本，因而容易造成安全隐患。因此在扩展性和性能以及安全性之间要做个取舍

另外本文的实现其实是借鉴了zuul动态更新filter的源码，感兴趣的朋友，可以通过下载zuul源码进行学习。不过也可以看xxl-job的groovy脚本实现，这个更简单点