1. AOP存在的问题

获取参数复杂
AOP的规则相对简单

2. 拦截器

2.1. 应用(以登录为例)

2.1.1. 自定义拦截器

新建interceptor文件夹

import org.springframework.web.servlet.HandlerInterceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@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
            return true;
        }else {
            //没登录
            response.setStatus(401);
            return false;
        }
    }
}

2.1.2. 将自定义拦截器加入到系统配置

新建config文件夹

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import springaop.interceptor.LoginInterceptor;

@Configuration
public class AppConfig implements WebMvcConfigurer {

    @Autowired
    private LoginInterceptor loginInterceptor;
    @Override
    public void addInterceptors(InterceptorRegistry registry) {

        registry.addInterceptor(loginInterceptor)
                .addPathPatterns("/**")         //"/**"表示拦截所有
                .excludePathPatterns("/user/login")  //除了登录
                .excludePathPatterns("/user/reg");    //除了注册
    }
}

2.1.3. 业务代码

import lombok.extern.slf4j.Slf4j;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

@Slf4j
@RequestMapping("/user")
@RestController
public class UserController {
    //获取用户信息
    @RequestMapping("/getInfo")
    public String getInfo(){
        log.info("log.getInfo");
        return "get info...";
    }

    //注册
    @RequestMapping("/reg")
    public String reg(){
        log.info("log.reg");
        return "reg...";
    }

    //登录
    @RequestMapping("/login")
    public boolean login(HttpServletRequest request,String username,String password){
        log.info("log.login");
        //判断username和password是否为空
//        if (username!=null && username.equals("") && password!=null && password.equals("")){
//            //
//        }
        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;
    }
}

2.2. 排除所有静态资源方法

方法1

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

方法2

private final List<String> excludePaths = 
    //注意List的这种方式的初始化赋值不允许再追加元素
    Arrays.asList("/**/*.html",
                  "blog-editormd",
                  "/css/**",
                  "/js/**",
                  "/pic/**",
                  "/user/login",
                  "/user/res");
	
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(loginInterceptor)
                .addPathPatterns("/**")
                .excludePathPatterns(excludePaths);
    }

2.3. 实现原理

2.3.1. 总体思路

2.3.2. 部分源码分析

拦截器是基于AOP实现的

(AOP基于动态代理(JDK|CGLIB))

3. 统一功能处理

3.1. 统一登录处理

参考上一节拦截器的应用

3.2. 统一异常处理

对于下面的异常, 我们在访问页面的时候,不希望让用户看到

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

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

    //空指针异常
    @RequestMapping("/test2")
    public boolean test2(){
        String str = null;
        System.out.println(str.length());
        return true;
    }

    //手动异常
    @RequestMapping("/test3")
    public boolean test3(){
        throw new RuntimeException("手动异常");
    }
}

可能出现的问题:

类上面的@RequestMapping("/ex")访问的时候会有未知的问题,改成@RequestMapping("/exception")比较好

3.2.1. 配置ErrorHandler

针对不同的异常,进行不同的操作

import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;

import java.util.HashMap;

@Slf4j
@ControllerAdvice
@ResponseBody
public class ErrorHandler {
    
    @ExceptionHandler
    public Object error(Exception e){
        HashMap<String,Object> result = new HashMap<>();
        log.info("内部异常:",e);
        result.put("success",0);
        result.put("code",-1);
        result.put("msg","内部异常");
        return result;
    }

    @ExceptionHandler
    public Object error(ArithmeticException e){
        HashMap<String,Object> result = new HashMap<>();
        log.info("算数异常:",e);
        result.put("success",0);
        result.put("code",-2);
        result.put("msg","算术异常");
        return result;
    }

    @ExceptionHandler
    public Object error(NullPointerException e){
        HashMap<String,Object> result = new HashMap<>();
        log.info("空指针异常:",e);
        result.put("success",0);
        result.put("code",-3);
        result.put("msg","空指针异常");
        return result;
    }
}

3.2.1.1. 可能会遇到的问题

①写完代码访问的时候,会是错误404, 而且异常是返回的不是一个视图, 需要添加@ResponseBody注解,让程序意识到返回的就是数据, 而不是视图

②分辨不出来异常

之前在切面的@Around环绕通知里有一段代码

要是遇到了异常都会抛出RuntimeException, 从而掩盖了真正的异常, 需要改成下面的样子, 抛出真正的异常

3.3. 统一数据返回格式

3.3.1. 好处

统一数据返回格式的优点有很多. 比如以下几个:

方便前端程序员更好的接收和解析后端数据接口返回的数据
降低前端程序员和后端程序员的沟通成本，按照某个格式实现就行了，因为所有接口都是这样返回的
有利于项目统一数据的维护和修改
有利于后端技术部门的统一规范的标准制定，不会出现稀奇古怪的返回内容

3.3.2. 代码

新建ResponseHandler

import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

import java.util.HashMap;

@ControllerAdvice
public class ResponseHandler implements ResponseBodyAdvice {
    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        return true;    //一定要改成true
    }

    @SneakyThrows
    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
        HashMap<String,Object> result = new HashMap<>();
        result.put("success",1);
        result.put("data",body);
        result.put("errMsg","");
        //对字符串进行特殊处理
        if (body instanceof String){
            ObjectMapper mapper = new ObjectMapper();
            return mapper.writeValueAsString(result);
        }
        return result;
    }
}

添加这段代码之前, 访问成功了,得到的是true, 加上这段代码就变成了{"data":true,"success":1,"errMsg":""}