springboot源码解析之Model和Map参数解析

标签:源码:springboot

测试代码

@Controller
public class HelloController {

    @RequestMapping("/helloModelAndMap")
    public String helloModelAndMap(HttpServletRequest request, Model model, Map<String, Object> map) {
        System.out.println(model.getClass().getSimpleName());
        System.out.println(map.getClass().getSimpleName());
        System.out.println(model == map);
        request.setAttribute("message", "Hello World!");
        model.addAttribute("name", "张三");
        map.put("age", 18);
        // 这里拿不到Model和Map中的值,转发后能拿到 在视图渲染阶段才会放到请求域中
        System.out.println("helloMapAndModel:" + request.getAttribute("name"));
        System.out.println("helloMapAndModel:" + request.getAttribute("age"));
        return "forward:/success";
    }

    @RequestMapping("/success")
    @ResponseBody
    public Object success(ServletRequest request) {
        Map<String, Object> result = new HashMap<>();
        result.put("message", request.getAttribute("message"));
        result.put("name", request.getAttribute("name"));
        result.put("age", request.getAttribute("age"));
        return result;
    }

}

控制台输出

BindingAwareModelMap
BindingAwareModelMap
true
helloMapAndModel:null
helloMapAndModel:null

请求响应

{"name":"张三","message":"Hello World!","age":18}

结果分析

通过输出可以看到,这里传入的Model对象和Map对象都是BindingAwareModelMap类型,并且指向同一个对象,BindingAwareModelMap既是Model也是Map

ModelAndViewContainer

public class ModelAndViewContainer {

   // ...

   private final ModelMap defaultModel = new BindingAwareModelMap();

  
   public ModelMap getModel() {
      if (useDefaultModel()) {
         return this.defaultModel;
      }
      else {
         if (this.redirectModel == null) {
            this.redirectModel = new ModelMap();
         }
         return this.redirectModel;
      }
   }

   // ... 

}

MapMethodProcessor

Map是由MapMethodProcessor参数处理器处理的

public class MapMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

   @Override
   public boolean supportsParameter(MethodParameter parameter) {
       // 参数类型为Map,并且没有啥注解(所以如果想要用map接受前段传递的请求体里的参数,一定要不要忘记加上@RequestBody注解)
      return Map.class.isAssignableFrom(parameter.getParameterType()) &&
            parameter.getParameterAnnotations().length == 0;
   }

   @Override
   @Nullable
   public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
         NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

      Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
       // 解析参数 这里拿到了ModelAndViewContainer 里面的Model 也就是 BindingAwareModelMap
      return mavContainer.getModel();
   }

   @Override
   public boolean supportsReturnType(MethodParameter returnType) {
      return Map.class.isAssignableFrom(returnType.getParameterType());
   }

   @Override
   @SuppressWarnings({"rawtypes", "unchecked"})
   public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
         ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

      if (returnValue instanceof Map){
         mavContainer.addAllAttributes((Map) returnValue);
      }
      else if (returnValue != null) {
         // should not happen
         throw new UnsupportedOperationException("Unexpected return type: " +
               returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
      }
   }

}

ModelMethodProcessor

Model参数是由ModelMethodProcessor解析的

public class ModelMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
        // 参数类型是model
		return Model.class.isAssignableFrom(parameter.getParameterType());
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
        // 解析参数 和 MapMethodProcessor 一样,拿到了同一个 BindingAwareModelMap 对象,这也就是为什么测试方法里面model 和 map指向同一个对象的原因
		return mavContainer.getModel();
	}

	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
		return Model.class.isAssignableFrom(returnType.getParameterType());
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

		if (returnValue == null) {
			return;
		}
		else if (returnValue instanceof Model) {
			mavContainer.addAllAttributes(((Model) returnValue).asMap());
		}
		else {
			// should not happen
			throw new UnsupportedOperationException("Unexpected return type: " +
					returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
		}
	}

}

参数解析过程中只是拿到了 BindingAwareModelMap 对象,执行目标方法的时候只是将key和value设置到了 BindingAwareModelMap 对象里面,那么具体是在哪里将 BindingAwareModelMap 中的key和value设置到请求域中的呢?

AbstractView

org.springframework.web.servlet.view.AbstractView#exposeModelAsRequestAttributes

protected void exposeModelAsRequestAttributes(Map<String, Object> model,
                                              HttpServletRequest request) throws Exception {

    model.forEach((name, value) -> {
        if (value != null) {
            // 这样就是为什么给model 和 map中方数据和给request放数据一样的原因
            request.setAttribute(name, value);
        }
        else {
            request.removeAttribute(name);
        }
    });
}