【探索Spring底层】14.谈谈参数解析器

拼搏现实的明天。 2024-03-30 11:46 29阅读 0赞

#### 文章目录 ####

*  1. 参数解析器概述
 *  2. 常见参数的解析

## 1. 参数解析器概述 ##

参数解析器是Spring-Web包提供的组件，并且SpringMVC中提供了很多参数解析器。

常见的参数解析器如下

*  `org.springframework.web.method.annotation.RequestParamMethodArgumentResolver@abbc908`
 *  `org.springframework.web.method.annotation.RequestParamMapMethodArgumentResolver@44afefd5`
 *  `org.springframework.web.servlet.mvc.method.annotation.PathVariableMethodArgumentResolver@9a7a808`
 *  `org.springframework.web.servlet.mvc.method.annotation.PathVariableMapMethodArgumentResolver@72209d93`
 *  `org.springframework.web.servlet.mvc.method.annotation.MatrixVariableMethodArgumentResolver@2687f956`
 *  `org.springframework.web.servlet.mvc.method.annotation.MatrixVariableMapMethodArgumentResolver@1ded7b14`
 *  `org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor@29be7749`
 *  `org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor@5f84abe8`
 *  `org.springframework.web.servlet.mvc.method.annotation.RequestPartMethodArgumentResolver@4650a407`
 *  `org.springframework.web.method.annotation.RequestHeaderMethodArgumentResolver@30135202`
 *  `org.springframework.web.method.annotation.RequestHeaderMapMethodArgumentResolver@6a4d7f76`
 *  `org.springframework.web.servlet.mvc.method.annotation.ServletCookieValueMethodArgumentResolver@10ec523c`
 *  `org.springframework.web.method.annotation.ExpressionValueMethodArgumentResolver@53dfacba`
 *  `org.springframework.web.servlet.mvc.method.annotation.SessionAttributeMethodArgumentResolver@79767781`
 *  `org.springframework.web.servlet.mvc.method.annotation.RequestAttributeMethodArgumentResolver@78411116`
 *  `org.springframework.web.servlet.mvc.method.annotation.ServletRequestMethodArgumentResolver@aced190`
 *  `org.springframework.web.servlet.mvc.method.annotation.ServletResponseMethodArgumentResolver@245a060f`
 *  `org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor@6edaa77a`
 *  `org.springframework.web.servlet.mvc.method.annotation.RedirectAttributesMethodArgumentResolver@1e63d216`
 *  `org.springframework.web.method.annotation.ModelMethodProcessor@62ddd21b`
 *  `org.springframework.web.method.annotation.MapMethodProcessor@16c3ca31`
 *  `org.springframework.web.method.annotation.ErrorsMethodArgumentResolve`

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## 2. 常见参数的解析 ##

我们在开发中，常用的参数如下

*  @RequestParam
 *  省略 @RequestParam
 *  @RequestParam(defaultValue)
 *  MultipartFile
 *  @PathVariable
 *  @RequestHeader
 *  @CookieValue
 *  @Value
 *  HttpServletRequest 等
 *  @ModelAttribute
 *  省略 @ModelAttribute
 *  @RequestBody

那么这些参数Spring到底是怎么解析的呢？

下面就来模拟一下吧

首先准备controller

static class Controller {
        
        public void test(
            @RequestParam("name1") String name1, // name1=张三
            String name2,                        // name2=李四
            @RequestParam("age") int age,        // age=18
            @RequestParam(name = "home", defaultValue = "${JAVA_HOME}") String home1, // spring 获取数据
            @RequestParam("file") MultipartFile file, // 上传文件
            @PathVariable("id") int id,               //  /test/124   /test/{id}
            @RequestHeader("Content-Type") String header,
            @CookieValue("token") String token,
            @Value("${JAVA_HOME}") String home2, // spring 获取数据  ${} #{}
            HttpServletRequest request,          // request, response, session ...
            @ModelAttribute("abc") User user1,          // name=zhang&age=18
            User user2,                          // name=zhang&age=18
            @RequestBody User user3              // json
        ) {
        
        }
    }

接着准备模拟请求

private static HttpServletRequest mockRequest() {
        
        MockHttpServletRequest request = new MockHttpServletRequest();
        request.setParameter("name1", "zhangsan");
        request.setParameter("name2", "lisi");
        request.addPart(new MockPart("file", "abc", "hello".getBytes(StandardCharsets.UTF_8)));
        Map<String, String> map = new AntPathMatcher().extractUriTemplateVariables("/test/{id}", "/test/123");
        System.out.println(map);
        request.setAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, map);
        request.setContentType("application/json");
        request.setCookies(new Cookie("token", "123456"));
        request.setParameter("name", "张三");
        request.setParameter("age", "18");
        request.setContent("""
                           {
                               "name":"李四",
                               "age":20
                           }
                           """.getBytes(StandardCharsets.UTF_8));
    
                           return new StandardServletMultipartResolver().resolveMultipart(request);
                           }

首先准备一个容器

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(WebConfig.class);

接着准备Request

HttpServletRequest request = mockRequest();

接着将controller类的方法封装成`HandlerMethod`

HandlerMethod handlerMethod = new HandlerMethod(new Controller(), Controller.class.getMethod("test", String.class, String.class, int.class, String.class, MultipartFile.class, int.class, String.class, String.class, String.class, HttpServletRequest.class, User.class, User.class, User.class));

接着准备对象绑定与类型转换

ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, null);

准备 ModelAndViewContainer 用来存储中间 Model 结果

ModelAndViewContainer container = new ModelAndViewContainer();

最后解析每个参数值

遍历`handlerMethod.getMethodParameters()`的`MethodParameter`

首先准备一个多解析器组合

HandlerMethodArgumentResolverComposite composite = new HandlerMethodArgumentResolverComposite();
    composite.addResolvers(
        //                                          false 表示必须有 @RequestParam
        new RequestParamMethodArgumentResolver(beanFactory, false),
        new PathVariableMethodArgumentResolver(),
        new RequestHeaderMethodArgumentResolver(beanFactory),
        new ServletCookieValueMethodArgumentResolver(beanFactory),
        new ExpressionValueMethodArgumentResolver(beanFactory),
        new ServletRequestMethodArgumentResolver(),
        new ServletModelAttributeMethodProcessor(false), // 必须有 @ModelAttribute
        new RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())),
        new ServletModelAttributeMethodProcessor(true), // 省略了 @ModelAttribute
        new RequestParamMethodArgumentResolver(beanFactory, true) // 省略 @RequestParam
    );

最后判断是否支持该参数，如果支持则进一步解析

String annotations = Arrays.stream(parameter.getParameterAnnotations()).map(a -> a.annotationType().getSimpleName()).collect(Collectors.joining());
    String str = annotations.length() > 0 ? " @" + annotations + " " : " ";
    //设置参数名发现者
    parameter.initParameterNameDiscovery(new DefaultParameterNameDiscoverer());
    
    if (composite.supportsParameter(parameter)) {
        
        // 支持此参数
        //解析出请求的结果
        Object v = composite.resolveArgument(parameter, container, new ServletWebRequest(request), factory);
        //                System.out.println(v.getClass());
        System.out.println("[" + parameter.getParameterIndex() + "] " + str + parameter.getParameterType().getSimpleName() + " " + parameter.getParameterName() + "->" + v);
        System.out.println("模型数据为：" + container.getModel());
    } else {
        
        System.out.println("[" + parameter.getParameterIndex() + "] " + str + parameter.getParameterType().getSimpleName() + " " + parameter.getParameterName());
    }

全部代码

public static void main(String[] args) throws Exception {
        
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(WebConfig.class);
        DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();
        // 准备测试 Request
        HttpServletRequest request = mockRequest();
    
        // 要点1. 控制器方法被封装为 HandlerMethod
        HandlerMethod handlerMethod = new HandlerMethod(new Controller(), Controller.class.getMethod("test", String.class, String.class, int.class, String.class, MultipartFile.class, int.class, String.class, String.class, String.class, HttpServletRequest.class, User.class, User.class, User.class));
    
        // 要点2. 准备对象绑定与类型转换
        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, null);
    
        // 要点3. 准备 ModelAndViewContainer 用来存储中间 Model 结果
        ModelAndViewContainer container = new ModelAndViewContainer();
    
        // 要点4. 解析每个参数值
        for (MethodParameter parameter : handlerMethod.getMethodParameters()) {
        
            // 多个解析器组合
            HandlerMethodArgumentResolverComposite composite = new HandlerMethodArgumentResolverComposite();
            composite.addResolvers(
                //                                          false 表示必须有 @RequestParam
                new RequestParamMethodArgumentResolver(beanFactory, false),
                new PathVariableMethodArgumentResolver(),
                new RequestHeaderMethodArgumentResolver(beanFactory),
                new ServletCookieValueMethodArgumentResolver(beanFactory),
                new ExpressionValueMethodArgumentResolver(beanFactory),
                new ServletRequestMethodArgumentResolver(),
                new ServletModelAttributeMethodProcessor(false), // 必须有 @ModelAttribute
                new RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())),
                new ServletModelAttributeMethodProcessor(true), // 省略了 @ModelAttribute
                new RequestParamMethodArgumentResolver(beanFactory, true) // 省略 @RequestParam
            );
    
            String annotations = Arrays.stream(parameter.getParameterAnnotations()).map(a -> a.annotationType().getSimpleName()).collect(Collectors.joining());
            String str = annotations.length() > 0 ? " @" + annotations + " " : " ";
            parameter.initParameterNameDiscovery(new DefaultParameterNameDiscoverer());
    
            if (composite.supportsParameter(parameter)) {
        
                // 支持此参数
                Object v = composite.resolveArgument(parameter, container, new ServletWebRequest(request), factory);
                //                System.out.println(v.getClass());
                System.out.println("[" + parameter.getParameterIndex() + "] " + str + parameter.getParameterType().getSimpleName() + " " + parameter.getParameterName() + "->" + v);
                System.out.println("模型数据为：" + container.getModel());
            } else {
        
                System.out.println("[" + parameter.getParameterIndex() + "] " + str + parameter.getParameterType().getSimpleName() + " " + parameter.getParameterName());
            }
        }
    
    }

![image-20221223213830065][]

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[image-20221223213830065]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/5f7b25a1519d401892d0304705c4821b.png