SpringMVC_08_报文消息转换器HttpMessageConverter

HttpMessageConverter

HttpMessageConverter，报文信息转换器，将请求报文转换为Java对象，或将Java对象转换为响应报文

HttpMessageConverter提供了两个注解和两个类型：@RequestBody，@ResponseBody，RequestEntity，ResponseEntity

@RequestBody

@RequestBody可以获取请求体，需要在控制器方法设置一个形参，使用@RequestBody进行标识，当前请求的请求体就会为当前注解所标识的形参赋值

<form th:action="@{/testRequestBody}" method="post">
    用户名：<input type="text" name="username"><br>
    密码：<input type="password" name="password"><br>
    <input type="submit">
</form>

@RequestMapping("/testRequestBody")
public String testRequestBody(@RequestBody String requestBody){
    System.out.println("requestBody:"+requestBody);
    return "success";
}

输出结果：requestBody:username=admin&password=123456

RequestEntity

RequestEntity封装请求报文的一种类型，需要在控制器方法的形参中设置该类型的形参，当前请求的请求报文就会赋值给该形参，可以通过getHeaders()获取请求头信息，通过getBody()获取请求体信息

@RequestMapping("/testRequestEntity")
public String testRequestEntity(RequestEntity<String> requestEntity){
    System.out.println("requestHeader:"+requestEntity.getHeaders());
    System.out.println("requestBody:"+requestEntity.getBody());
    return "success";
}

输出结果： requestHeader:[host:"localhost:8080", connection:"keep-alive", content-length:"27", cache-control:"max-age=0", sec-ch-ua:"" Not A;Brand";v="99", "Chromium";v="90", "Google Chrome";v="90"", sec-ch-ua-mobile:"?0", upgrade-insecure-requests:"1", origin:"http://localhost:8080", user-agent:"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.93 Safari/537.36"] requestBody:username=admin&password=123

@ResponseBody

@ResponseBody用于标识一个控制器方法，可以将该方法的返回值直接作为响应报文的响应体响应到浏览器

@RequestMapping("/testResponseBody")
@ResponseBody
public String testResponseBody(){
    return "success";
}

结果：浏览器页面显示success

SpringMVC处理json

@ResponseBody处理json的步骤：

a>导入jackson的依赖

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.12.1</version>
</dependency>

b>在SpringMVC的核心配置文件中开启mvc的注解驱动，此时在HandlerAdaptor中会自动装配一个消息转换器：MappingJackson2HttpMessageConverter，可以将响应到浏览器的Java对象转换为Json格式的字符串

<mvc:annotation-driven />

c>在处理器方法上使用@ResponseBody注解进行标识

d>将Java对象直接作为控制器方法的返回值返回，就会自动转换为Json格式的字符串

@RequestMapping("/testResponseUser")
@ResponseBody
public User testResponseUser(){
    return new User(1001,"admin","123456",23,"男");
}

浏览器的页面中展示的结果：

{"id":1001,"username":"admin","password":"123456","age":23,"sex":"男"}

SpringMVC处理ajax

a>请求超链接：

<div id="app">
	<a th:href="@{/testAjax}" @click="testAjax">testAjax</a><br>
</div>

b>通过vue和axios处理点击事件：

<script type="text/javascript" th:src="@{/static/js/vue.js}"></script>
<script type="text/javascript" th:src="@{/static/js/axios.min.js}"></script>
<script type="text/javascript">
    var vue = new Vue({
        el:"#app",
        methods:{
            testAjax:function (event) {
                axios({
                    method:"post",
                    url:event.target.href,
                    params:{
                        username:"admin",
                        password:"123456"
                    }
                }).then(function (response) {
                    alert(response.data);
                });
                event.preventDefault();
            }
        }
    });
</script>

c>控制器方法：

@RequestMapping("/testAjax")
@ResponseBody
public String testAjax(String username, String password){
    System.out.println("username:"+username+",password:"+password);
    return "hello,ajax";
}

@RestController注解

@RestController注解是springMVC提供的一个复合注解，标识在控制器的类上，就相当于为类添加了@Controller注解，并且为其中的每个方法添加了@ResponseBody注解

ResponseEntity

ResponseEntity用于控制器方法的返回值类型，该控制器方法的返回值就是响应到浏览器的响应报文

完整代码

@Controller
public class HttpController {

    @RequestMapping("/testRequestBody")
    public String testRequestBody(@RequestBody String requestBody){
        System.out.println("requestBody"+requestBody);
        return "success";

    }

    @RequestMapping("/testRequestEntity")
    public String testRequestEntity(RequestEntity<String> requestEntity){
        //当前requestEntity表示整个请求报文的信息
        System.out.println("请求头:"+requestEntity.getHeaders());
        System.out.println("请求体:"+requestEntity.getBody());

        return "success";
    }

    @RequestMapping("/testResponse")
    public void testResponse(HttpServletResponse response) throws Exception{
        response.getWriter().print("hello,response");
    }

    @RequestMapping("/testResponseBody")
    @ResponseBody
    public String testResponseBody(){
        return "success";
    }

    @RequestMapping("/testResponseUser")
    @ResponseBody
    public User testResponseUser(){
        return new User(1001,"admin","123456",20,"男");
    }

    @RequestMapping("/testAxios")
    @ResponseBody
    public String testAxios(String username,String password){
        System.out.println(username+","+password);
        return "hello,axios";

    }
}

public class User {
    private Integer id;

    private String username;

    private String password;

    private Integer age;

    private String sex;

    public User(Integer id, String username, String password, Integer age, String sex) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
        this.sex = sex;
    }

    public User() {
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

}

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>success</h1>
</body>
</html>

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>首页</title>
</head>
<body>
<h1>首页</h1>
<form th:action="@{/testRequestBody}" method="post">
    <input type="text" name="username">
    <input type="text" name="password">
    <input type="submit" name="测试@RequestBody">
</form>
<form th:action="@{/testRequestEntity}" method="post">
<input type="text" name="username">
<input type="text" name="password">
<input type="submit" name="测试RequestEntity">
</form>

<a th:href="@{/testResponse}">通过servletAPI的response对象响应浏览器数据</a>
<a th:href="@{/testResponseBody}">通过@ResquestBody响应浏览器数据</a>
<a th:href="@{/testResponseUser}">通过@ResquestUser响应浏览器User对象</a>
<div id="app">
    <a @Click="textAxios" th:href="@{/testAxios}">Spring处理ajax</a>
</div>
<script type="text/javascript" th:src="@{/static/js/vue.js}"></script>
<script type="text/javascript" th:src="@{/static/js/axios.min.js}"></script>
<script type="text/javascript" >
    new Vue({
        el:"#app",
        methods:{
            testAxios:function (event){
                axios({
                    method: "post",
                    url:event.target.href,
                    params:{
                        username:"admin",
                        password:"123456"
                    }
                }).then(function (response) {
                    alert(response.data);
                });
                event.preventDefault();

            }
        }
    });
</script>
</body>
</html>

参考：https://frxcat.fun/

拓展mvc框架的消息转换器

@Slf4j
@Configuration
public class WebMvcConfig extends WebMvcConfigurationSupport {
    /**
     * 设置静态资源映射
     * @param registry
     */
    @Override
    protected void addResourceHandlers(ResourceHandlerRegistry registry) {
        log.info("开始进行静态资源映射");
        // 对所有/backend/**开头的请求，添加映射到resources下的backend文件夹下
        registry.addResourceHandler("/backend/**").addResourceLocations("classpath:/backend/");
        registry.addResourceHandler("/front/**").addResourceLocations("classpath:/front/");
    }

    /**
     * 拓展mvc框架的消息转换器（实现json转换为java对象）
     * @param converters
     */
    @Override
    protected void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
        log.info("拓展消息转换器...");
        //创建消息转换器对象
        MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();
        //设置对象转换器，底层使用Jaskson将java对象转为json
        messageConverter.setObjectMapper(new JacksonObjectMapper());
        //将上面的消息转换器对象追加到mvc框架的转换器集合中
        converters.add(0,messageConverter);//0表示放在最前面，最优先使用
        super.extendMessageConverters(converters);
    }
}