03 HandlerMapping拦截器

上一节的内容稍多，所以本小节的内容设置相对简单，主要来实现SmartMVC中的拦截器部分，首先我还是来看下本小节涉及到的类图，以及这些类需要提供的方法

4.1 开发步骤讲解

本节源码所在分支： handlerMapping-interceptor

HandlerInterceptor

首先我们来定义HandlerInterceptor接口，提供了三个方法：

preHandle: 在执行Handler之前被调用，如果返回的是false，那么Handler就不会在执行
postHandle: 在Handler执行完成之后被调用，可以获取Handler返回的结果ModelAndView
afterCompletion: 该方法是无论什么情况下都会被调用，比如：preHandle返回false，Handler执行过程中抛出异常，Handler正常执行完成

public interface HandlerInterceptor {

    default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        return true;
    }

    default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                            @Nullable ModelAndView modelAndView) throws Exception {
    }

    default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
                                 @Nullable Exception ex) throws Exception {
    }
}

MappedInterceptor

我们都知道通常拦截器是需要设置对哪些URL生效的，但是从上面的拦截器接口定义我们没看到类设置，为了达到配置与业务的分离，所以我们又建立MappedInterceptor。MappedInterceptor所需要完成的功能：

作为真正HandlerInterceptor的代理类，所以需要继承于HandlerInterceptor，实现HandlerInterceptor的三个接口，并且内部需要包含真正HandlerInterceptor的实例
管理interceptor对哪些URL生效，排除哪些URL
提供match功能，调用方传入path，判断当前HandlerInterceptor是否支持本次请求。该功能简单实现，只支持path的完整匹配，需要了解更复杂的匹配请查看SpringMVC中的MappedInterceptor

完整代码如下：

public class MappedInterceptor implements HandlerInterceptor {
    private List<String> includePatterns = new ArrayList<>();
    private List<String> excludePatterns = new ArrayList<>();

    private HandlerInterceptor interceptor;

    public MappedInterceptor(HandlerInterceptor interceptor) {
        this.interceptor = interceptor;
    }

    /**
     * 添加支持的path
     *
     * @param patterns
     * @return
     */
    public MappedInterceptor addIncludePatterns(String... patterns) {
        this.includePatterns.addAll(Arrays.asList(patterns));
        return this;
    }

    /**
     * 添加排除的path
     *
     * @param patterns
     * @return
     */
    public MappedInterceptor addExcludePatterns(String... patterns) {
        this.excludePatterns.addAll(Arrays.asList(patterns));
        return this;
    }


    /**
     * 根据传入的path, 判断当前的interceptor是否支持
     *
     * @param lookupPath
     * @return
     */
    public boolean matches(String lookupPath) {
        if (!CollectionUtils.isEmpty(this.excludePatterns)) {
            if (excludePatterns.contains(lookupPath)) {
                return false;
            }
        }
        if (ObjectUtils.isEmpty(this.includePatterns)) {
            return true;
        }
        if (includePatterns.contains(lookupPath)) {
            return true;
        }
        return false;
    }


    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        return this.interceptor.preHandle(request, response, handler);
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           @Nullable ModelAndView modelAndView) throws Exception {
        this.interceptor.postHandle(request, response, handler, modelAndView);
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
                                @Nullable Exception ex) throws Exception {
        this.interceptor.afterCompletion(request, response, handler, ex);
    }
}

InterceptorRegistry

现在我们已经开发完了处理拦截业务逻辑的接口HandlerInterceptor，管理HandlerInterceptor与请求路径的映射关联类MappedInterceptor，我们还缺少一个拦截器的注册中心管理所有的拦截器，试想下如果没有这个，那么当需要获取项目中所有拦截器的时候就会很难受，所以我们还需要建了一个InterceptorRegistry

public class InterceptorRegistry {
    private List<MappedInterceptor> mappedInterceptors = new ArrayList<>();

    /**
     * 注册一个拦截器到Registry
     * @param interceptor
     * @return
     */
    public MappedInterceptor addInterceptor(HandlerInterceptor interceptor) {
        MappedInterceptor mappedInterceptor = new MappedInterceptor(interceptor);
        mappedInterceptors.add(mappedInterceptor);
        return mappedInterceptor;
    }

    public List<MappedInterceptor> getMappedInterceptors() {
        return mappedInterceptors;
    }
}

4.2 单元测试

到此我们拦截器的功能都开发完，虽然简单，但是我们还是需要做一些单元测试，测试用例：

创建一个拦截器的实现，能够正常的注册到InterceptorRegistry
能够为注册的拦截器设置支持URL和排除的URL
测试拦截器的match方法是否正确

拦截器的实现类TestHandlerInterceptor

public class TestHandlerInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("TestHandlerInterceptor => preHandle");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("TestHandlerInterceptor => postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("TestHandlerInterceptor => afterCompletion");
    }
}

根据刚才写的单元测试用例编写单元测试：

public class HandlerInterceptorTest {

    private InterceptorRegistry interceptorRegistry = new InterceptorRegistry();

    @Test
    public void test() throws Exception {
        TestHandlerInterceptor interceptor = new TestHandlerInterceptor();

        interceptorRegistry.addInterceptor(interceptor)
                .addExcludePatterns("/ex_test")
                .addIncludePatterns("/in_test");

        List<MappedInterceptor> interceptors = interceptorRegistry.getMappedInterceptors();

        Assert.assertEquals(interceptors.size(), 1);

        MappedInterceptor mappedInterceptor = interceptors.get(0);

        Assert.assertTrue(mappedInterceptor.matches("/in_test"));
        Assert.assertFalse(mappedInterceptor.matches("/ex_test"));

        mappedInterceptor.preHandle(null, null, null);
        mappedInterceptor.postHandle(null, null, null, null);
        mappedInterceptor.afterCompletion(null, null, null, null);
    }

}

运行的结果：

4.3 本节小结

本节我们完成了拦截器相关逻辑的开发，如果有面试官问HandlerInterceptor中的afterCompletion方法在哪些情况下会执行，我们应该能回答了

4.4 延展

本节实现的拦截器和SpringMVC提供的拦截器有些许差别，功能也不如SpringMVC的强大，大家可以对比着看看，加深对SpringMVC拦截器的理解

03 Middleware

04 Algorithms

4.1 开发步骤讲解

HandlerInterceptor

MappedInterceptor

InterceptorRegistry

4.2 单元测试

4.3 本节小结

4.4 延展

4.1 开发步骤讲解 ​

HandlerInterceptor ​

MappedInterceptor ​

InterceptorRegistry ​

4.2 单元测试 ​

4.3 本节小结 ​

4.4 延展 ​

4.1 开发步骤讲解

HandlerInterceptor

MappedInterceptor

InterceptorRegistry

4.2 单元测试

4.3 本节小结

4.4 延展