SpringMVC如何处理controller的各种返回类型

Question

本人小白，求教一下各位大神，springMVC的controller的返回值都可以是什么类型？
然后springMVC对于各种返回类型是怎么处理的。
比如，我知道，如果controller返回string类型的值，那么springMVC会根据视图解析器拼接得到url，从而知道目标视图。
那么，当controlloer返回Map类型、void类型、ModelAndView（有些ModelAndView设置了viewName，有些又没设置），对于这些类型，springMVC框架都是如何处理。

Answer 1

对于springMVC处理方法支持支持一系列的返回方式：
1.ModelAndView
2.Model
3.ModelMap
4.Map
5.View
6.String
7.ResponseEntity

---

一.ModelAndView
@RequestMapping("/test")public ModelAndView list(@ModelAttribute("id") String id,HttpServletRequest request) { ModelAndView mv = new ModelAndView(); //ModelAndView mv = new ModelAndView("test"); mv.addObject("name", "test"); mv.setViewName("test");//如用上面注释的可去掉这句 return mv;}
ModelAndView构造函数可以指定返回页面的名称，也可以通过setViewName方法来设置所需要跳转的页面，并且返回的是一个包含模型和视图的ModelAndView对象；
二.Model
Model是一个借口，并不能直接返回，作用是作为一个模型对象包含了封装好的Model和modelMap,以及java.util.Map，当没有视图返回的时候视图名称将由requestToViewNameTranslator决定；
本人水平有限，可能描述的不够到位，附上spring里这个类的源码
/* * Copyright 2002-2012 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. /package org.springframework.ui;import java.util.Collection;import java.util.Map;/* * Java-5-specific interface that defines a holder for model attributes. * Primarily designed for adding attributes to the model. * Allows for accessing the overall model as a {@code java.util.Map}. * * @author Juergen Hoeller * @since 2.5.1 /public interface Model { /* * Add the supplied attribute under the supplied name. * @param attributeName the name of the model attribute (never {@code null}) * @param attributeValue the model attribute value (can be {@code null}) / Model addAttribute(String attributeName, Object attributeValue); /* * Add the supplied attribute to this {@code Map} using a * {@link org.springframework.core.Conventions#getVariableName generated name}. *
Note: Empty {@link java.util.Collection Collections} are not added to * the model when using this method because we cannot correctly determine * the true convention name. View code should check for {@code null} rather * than for empty collections as is already done by JSTL tags. * @param attributeValue the model attribute value (never {@code null}) / Model addAttribute(Object attributeValue); /* * Copy all attributes in the supplied {@code Collection} into this * {@code Map}, using attribute name generation for each element. * @see #addAttribute(Object) / Model addAllAttributes(Collection attributeValues); /* * Copy all attributes in the supplied {@code Map} into this {@code Map}. * @see #addAttribute(String, Object) / Model addAllAttributes(Map attributes); /* * Copy all attributes in the supplied {@code Map} into this {@code Map}, * with existing objects of the same name taking precedence (i.e. not getting * replaced). / Model mergeAttributes(Map attributes); /* * Does this model contain an attribute of the given name? * @param attributeName the name of the model attribute (never {@code null}) * @return whether this model contains a corresponding attribute / boolean containsAttribute(String attributeName); /* * Return the current set of model attributes as a Map. / Map asMap();}

三.ModelMap
在spring mvc中可以通过ModelMap对象传递模型参数到视图进行处理。在Controller方法中声明一个ModelMap参数，spring会创建一个ModelMap对象，并传入方法，方法处理完成后自动传递到视图进行处理。
ModelMap对象主要用于传递控制方法处理数据到结果页面，也就是说我们把结果页面上需要的数据放到ModelMap对象中即可，他的作用类似于request对象的setAttribute方法的作用，用来在一个请求过程中传递处理的数据。
@RequestMapping("/test") public String testmethod(String someparam,ModelMap model) { model.addAttribute("test","test"); // 返回跳转地址 return "path:handleok"; }
PS：建议使用ModelAndView
四.Map
这个个人感觉没什么可以介绍的，直接上代码
@RequestMapping(value = "/test") public Map index() { Map map = new HashMap(); map.put("test", "test"); // map.put相当于request.setAttribute方法 return map; }
五.View
View同Model一样也是一个接口，了解不多，上源码，欢迎补充
/ * Copyright 2002-2012 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. /package org.springframework.web.servlet;import java.util.Map;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.springframework.http.MediaType;/* * MVC View for a web interaction. Implementations are responsible for rendering * content, and exposing the model. A single view exposes multiple model attributes. * *
This class and the MVC approach associated with it is discussed in Chapter 12 of * Expert One-On-One J2EE Design and Development * by Rod Johnson (Wrox, 2002). * *
View implementations may differ widely. An obvious implementation would be * JSP-based. Other implementations might be XSLT-based, or use an HTML generation library. * This interface is designed to avoid restricting the range of possible implementations. * *
Views should be beans. They are likely to be instantiated as beans by a ViewResolver. * As this interface is stateless, view implementations should be thread-safe. * * @author Rod Johnson * @author Arjen Poutsma * @see org.springframework.web.servlet.view.AbstractView * @see org.springframework.web.servlet.view.InternalResourceView /public interface View { /* * Name of the {@link HttpServletRequest} attribute that contains the response status code. *
Note: This attribute is not required to be supported by all View implementations. / String RESPONSE_STATUS_ATTRIBUTE = View.class.getName() + ".responseStatus"; /* * Name of the {@link HttpServletRequest} attribute that contains a Map with path variables. * The map consists of String-based URI template variable names as keys and their corresponding * Object-based values -- extracted from segments of the URL and type converted. * *
Note: This attribute is not required to be supported by all View implementations. / String PATH_VARIABLES = View.class.getName() + ".pathVariables"; /* * The {@link MediaType} selected during content negotiation, which may be * more specific than the one the View is configured with. For example: * "application/vnd.example-v1+xml" vs "application/*+xml". / String SELECTED_CONTENT_TYPE = View.class.getName() + ".selectedContentType"; /* * Return the content type of the view, if predetermined. *
Can be used to check the content type upfront, * before the actual rendering process. * @return the content type String (optionally including a character set), * or {@code null} if not predetermined. / String getContentType(); /* * Render the view given the specified model. *
The first step will be preparing the request: In the JSP case, * this would mean setting model objects as request attributes. * The second step will be the actual rendering of the view, * for example including the JSP via a RequestDispatcher. * @param model Map with name Strings as keys and corresponding model * objects as values (Map can also be {@code null} in case of empty model) * @param request current HTTP request * @param response HTTP response we are building * @throws Exception if rendering failed */ void render(Map model, HttpServletRequest request, HttpServletResponse response) throws Exception;}

六.String
有2种返回方式：
String 指定返回的视图页面名称，结合设置的返回地址路径加上页面名称后缀即可访问到。
@RequestMapping("/test") public String welcomeHandler() { return "index"; }
简单粗暴，对应的逻辑视图名为“index”，URL= prefix前缀+视图名称 +suffix后缀。
第2种返回字符串
@RequestMapping(value = "/test") @ResponseBody public String lista(HttpServletRequest request) { return "test"; }
七.ResponseEntity
ResponseEntity作用比较强大,可以返回文件，字符串等
字符串的demo：
@RequestMapping(value = "/test", method = RequestMethod.POST, produces = "text/plain;charset=UTF-8;") public ResponseEntity test(HttpServletResponse response) { return new ResponseEntity("这是测试", HttpStatus.OK); }
文件的demo：
@RequestMapping("download") public ResponseEntity download(String filepath) throws IOException { HttpHeaders headers = new HttpHeaders(); headers.setContentType(MediaType.APPLICATION_OCTET_STREAM); headers.setContentDispositionFormData("attachment", "filename.suffix"); File file = new File(filepath); return new ResponseEntity(FileUtils.readFileToByteArray(file), headers, HttpStatus.CREATED); }
PS:使用ResponseEntity需要正确配置AnnotationMethodHandlerAdapter，messageConverters中的list是有顺序的，这点很重要！