SpringBoot 统⼀功能处理

⽤户登录权限效验

⽤户登录权限的发展从之前每个⽅法中⾃⼰验证⽤户登录权限，到现在统⼀的⽤户登录验证处理，它是⼀个逐渐完善和逐渐优化的过程。
Spring 中提供了具体的实现拦截器：HandlerInterceptor，拦截器的实现分为以下两个步骤：

1. 创建⾃定义拦截器，实现 HandlerInterceptor 接⼝的 preHandle（执⾏具体⽅法之前的预处理）⽅法。
2. 将⾃定义拦截器加⼊ WebMvcConfigurer 的 addInterceptors ⽅法中.

步骤:

controller层

@Slf4j
@RequestMapping("/user")
@RestController
public class UserController {
    //获取用户信息
    @RequestMapping("/getInfo")
    public String getInfo(){
        log.info("get info...");
        return "get info....";
    }
    //注册
    @RequestMapping("/reg")
    public String reg(){
        log.info("reg....");
//        int a = 10/0;
        return "reg....";
    }
    //login
    @RequestMapping("/login")
    public boolean login(HttpServletRequest request,String username,String password){
        log.info("login...");
        //判断username&password是否为空
//        if (username!=null && "".equals(username) && password!=null && "".equals(password)){
//
//        }
        if (!StringUtils.hasLength(username) || !StringUtils.hasLength(password)){
            return false;
        }
        if (!"admin".equals(username) || !"admin".equals(password)){
            return false;
        }
        HttpSession session = request.getSession(true);
        session.setAttribute("username", username);
        return true;
    }

}

⾃定义拦截器:

@Component
public class LoginInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //判断是否登录
        HttpSession session = request.getSession(false);
        if (session!=null && session.getAttribute("username")!=null){
            //通过,不进行拦截
            return true;
        }
        response.setStatus(401);
        return false;
    }
}

将⾃定义拦截器加⼊到系统配置:

@Configuration
public class AppConfig implements WebMvcConfigurer {
    @Autowired
    private LoginInterceptor loginInterceptor;
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(loginInterceptor)
                .addPathPatterns("/**")// 拦截所有url
                .excludePathPatterns("/user/login")
                .excludePathPatterns("/user/reg");
    }
}

其中：
addPathPatterns：表示需要拦截的 URL，“**”表示拦截任意⽅法（也就是所有⽅法）。
excludePathPatterns：表示需要排除的 URL。
说明：以上拦截规则可以拦截此项⽬中的使⽤ URL，包括静态⽂件（图⽚⽂件、JS 和 CSS 等⽂件）

排除所有的静态资源:

@Override
public void addInterceptors(InterceptorRegistry registry) {
 registry.addInterceptor(new LoginInterceptor())
 .addPathPatterns("/**") // 拦截所有接⼝
 .excludePathPatterns("/**/*.js")
 .excludePathPatterns("/**/*.css")
 .excludePathPatterns("/**/*.jpg")
 .excludePathPatterns("/login.html")
 .excludePathPatterns("/**/login"); // 排除接⼝
}

拦截器实现原理

正常情况下的调⽤顺序

然⽽有了拦截器之后，会在调⽤ Controller 之前进⾏相应的业务处理，执⾏的流程如下图所示

实现原理源码分析

所有的 Controller 执⾏都会通过⼀个调度器 DispatcherServlet 来实现，这⼀点可以从 Spring Boot 控
制台的打印信息看出，如下图所示

⽽所有⽅法都会执⾏ DispatcherServlet 中的 doDispatch 调度⽅法，doDispatch 源码如下

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            try {
                ModelAndView mv = null;
                Exception dispatchException = null;

                try {
                    processedRequest = this.checkMultipart(request);
                    multipartRequestParsed = processedRequest != request;
                    mappedHandler = this.getHandler(processedRequest);
                    if (mappedHandler == null) {
                        this.noHandlerFound(processedRequest, response);
                        return;
                    }

                    HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
                    String method = request.getMethod();
                    boolean isGet = HttpMethod.GET.matches(method);
                    if (isGet || HttpMethod.HEAD.matches(method)) {
                        long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                        if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
                            return;
                        }
                    }
                	// 预处理拦截器
                    if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                        return;
                    }
                	// 执行controller代码
                    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                    if (asyncManager.isConcurrentHandlingStarted()) {
                        return;
                    }

                    this.applyDefaultViewName(processedRequest, mv);
                    mappedHandler.applyPostHandle(processedRequest, response, mv);
                } catch (Exception var20) {
                    dispatchException = var20;
                } catch (Throwable var21) {
                    dispatchException = new NestedServletException("Handler dispatch failed", var21);
                }

                this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
            } catch (Exception var22) {
                this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
            } catch (Throwable var23) {
                this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
            }

        } finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            } else if (multipartRequestParsed) {
                this.cleanupMultipart(processedRequest);
            }

        }
    }

从上述源码可以看出在开始执⾏ Controller 之前，会先调⽤ 预处理⽅法 applyPreHandle，⽽
applyPreHandle ⽅法的实现源码如下：

 boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
        for(int i = 0; i < this.interceptorList.size(); this.interceptorIndex = i++) {
            HandlerInterceptor interceptor = (HandlerInterceptor)this.interceptorList.get(i);
            if (!interceptor.preHandle(request, response, this.handler)) {
                this.triggerAfterCompletion(request, response, (Exception)null);
                return false;
            }
        }

        return true;
    }

从上述源码可以看出，在 applyPreHandle 中会获取所有的拦截器 HandlerInterceptor 并执⾏拦截器中
的 preHandle ⽅法，这样就会前⾯定义的拦截器对应上了.
此时⽤户登录权限的验证⽅法就会执⾏，这就是拦截器的实现原理.

小结:

Spring 中的拦截器也是通过动态代理和环绕通知的思想实现的:

扩展：统⼀访问前缀添加:

// 所有的接⼝添加 api 前缀
    @Override
    public void configurePathMatch(PathMatchConfigurer configurer) {
        configurer.addPathPrefix("api", c -> true);
    }

统⼀异常处理

统⼀异常处理使⽤的是 @ControllerAdvice + @ExceptionHandler 来实现的，@ControllerAdvice 表
示控制器通知类，@ExceptionHandler 是异常处理器，两个结合表示当出现异常的时候执⾏某个通知，也就是执⾏某个⽅法事件.
config层:

@Slf4j
@ResponseBody
@ControllerAdvice
public class ErrorHandler {
//⽅法名和返回值可以⾃定义，其中最重要的是 @ExceptionHandler(Exception.class) 注解
//    @ResponseBody
    @ExceptionHandler
    public Object error(Exception e){
        HashMap<String,Object> result = new HashMap<>();
        result.put("success",0);
        result.put("code",-1);
        result.put("msg","内部异常");
        log.info("Exception: ",e);
        return result;
    }
}

在 controller层中设置⼀个异常，实现代码如下

@RequestMapping("/ex")
@RestController
public class ExceptionController {
    @RequestMapping("/test1")
    public boolean test1(){
        int a = 10/0;
        return true;
    }
}