40、响应处理-【源码分析】-基于请求参数的内容协商原理
上一节内容协商原理的第二步：
获取客户端（PostMan、浏览器）支持接收的内容类型。（获取客户端Accept请求头字段application/xml）
contentNegotiationManager内容协商管理器 默认使用基于请求头的策略HeaderContentNegotiationStrategy确定客户端可以接收的内容类型
//RequestResponseBodyMethodProcessor继承这类
public abstract class AbstractMessageConverterMethodProcessor extends AbstractMessageConverterMethodArgumentResolver
implements HandlerMethodReturnValueHandler {
...
//跟上一节的代码一致
protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
Object body;
Class<?> valueType;
Type targetType;
...
//本节重点
//内容协商（浏览器默认会以请求头(参数Accept)的方式告诉服务器他能接受什么样的内容类型）
MediaType selectedMediaType = null;
MediaType contentType = outputMessage.getHeaders().getContentType();
boolean isContentTypePreset = contentType != null && contentType.isConcrete();
if (isContentTypePreset) {
if (logger.isDebugEnabled()) {
logger.debug("Found 'Content-Type:" + contentType + "' in response");
}
selectedMediaType = contentType;
}
else {
HttpServletRequest request = inputMessage.getServletRequest();
List<MediaType> acceptableTypes = getAcceptableMediaTypes(request);
//服务器最终根据自己自身的能力，决定服务器能生产出什么样内容类型的数据
List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);
...
}
//在AbstractMessageConverterMethodArgumentResolver类内
private List<MediaType> getAcceptableMediaTypes(HttpServletRequest request)
throws HttpMediaTypeNotAcceptableException {
//内容协商管理器 默认使用基于请求头的策略
return this.contentNegotiationManager.resolveMediaTypes(new ServletWebRequest(request));
}
}
public class ContentNegotiationManager implements ContentNegotiationStrategy, MediaTypeFileExtensionResolver {
...
public ContentNegotiationManager() {
this(new HeaderContentNegotiationStrategy());//内容协商管理器 默认使用基于请求头的策略
}
@Override
public List<MediaType> resolveMediaTypes(NativeWebRequest request) throws HttpMediaTypeNotAcceptableException {
for (ContentNegotiationStrategy strategy : this.strategies) {
List<MediaType> mediaTypes = strategy.resolveMediaTypes(request);
if (mediaTypes.equals(MEDIA_TYPE_ALL_LIST)) {
continue;
}
return mediaTypes;
}
return MEDIA_TYPE_ALL_LIST;
}
...
}
//基于请求头的策略
public class HeaderContentNegotiationStrategy implements ContentNegotiationStrategy {
/**
* {@inheritDoc}
* @throws HttpMediaTypeNotAcceptableException if the 'Accept' header cannot be parsed
*/
@Override
public List<MediaType> resolveMediaTypes(NativeWebRequest request)
throws HttpMediaTypeNotAcceptableException {
String[] headerValueArray = request.getHeaderValues(HttpHeaders.ACCEPT);
if (headerValueArray == null) {
return MEDIA_TYPE_ALL_LIST;
}
List<String> headerValues = Arrays.asList(headerValueArray);
try {
List<MediaType> mediaTypes = MediaType.parseMediaTypes(headerValues);
MediaType.sortBySpecificityAndQuality(mediaTypes);
return !CollectionUtils.isEmpty(mediaTypes) ? mediaTypes : MEDIA_TYPE_ALL_LIST;
}
catch (InvalidMediaTypeException ex) {
throw new HttpMediaTypeNotAcceptableException(
"Could not parse 'Accept' header " + headerValues + ": " + ex.getMessage());
}
}
}
开启浏览器参数方式内容协商功能
为了方便内容协商，开启基于请求参数的内容协商功能。
spring:
mvc:
contentnegotiation:
favor-parameter: true #开启请求参数内容协商模式
内容协商管理器，就会多了一个ParameterContentNegotiationStrategy（由Spring容器注入）
public class ParameterContentNegotiationStrategy extends AbstractMappingContentNegotiationStrategy {
private String parameterName = "format";//
/**
* Create an instance with the given map of file extensions and media types.
*/
public ParameterContentNegotiationStrategy(Map<String, MediaType> mediaTypes) {
super(mediaTypes);
}
/**
* Set the name of the parameter to use to determine requested media types.
* <p>By default this is set to {@code "format"}.
*/
public void setParameterName(String parameterName) {
Assert.notNull(parameterName, "'parameterName' is required");
this.parameterName = parameterName;
}
public String getParameterName() {
return this.parameterName;
}
@Override
@Nullable
protected String getMediaTypeKey(NativeWebRequest request) {
return request.getParameter(getParameterName());
}
//---以下方法在AbstractMappingContentNegotiationStrategy类
@Override
public List<MediaType> resolveMediaTypes(NativeWebRequest webRequest)
throws HttpMediaTypeNotAcceptableException {
return resolveMediaTypeKey(webRequest, getMediaTypeKey(webRequest));
}
/**
* An alternative to {@link #resolveMediaTypes(NativeWebRequest)} that accepts
* an already extracted key.
* @since 3.2.16
*/
public List<MediaType> resolveMediaTypeKey(NativeWebRequest webRequest, @Nullable String key)
throws HttpMediaTypeNotAcceptableException {
if (StringUtils.hasText(key)) {
MediaType mediaType = lookupMediaType(key);
if (mediaType != null) {
handleMatch(key, mediaType);
return Collections.singletonList(mediaType);
}
mediaType = handleNoMatch(webRequest, key);
if (mediaType != null) {
addMapping(key, mediaType);
return Collections.singletonList(mediaType);
}
}
return MEDIA_TYPE_ALL_LIST;
}
}
然后，浏览器地址输入带format参数的URL：
http://localhost:8080/test/person?format=json
或
http://localhost:8080/test/person?format=xml
这样，后端会根据参数format的值，返回对应json或xml格式的数据。
41、响应处理-【源码分析】-自定义MessageConverter
实现多协议数据兼容。json、xml、x-guigu（这个是自创的）
@ResponseBody响应数据出去 调用RequestResponseBodyMethodProcessor处理Processor 处理方法返回值。通过
MessageConverter处理所有
MessageConverter合起来可以支持各种媒体类型数据的操作（读、写）内容协商找到最终的
messageConverter
SpringMVC的什么功能，一个入口给容器中添加一个 WebMvcConfigurer
@Configuration(proxyBeanMethods = false)
public class WebConfig {
@Bean
public WebMvcConfigurer webMvcConfigurer(){
return new WebMvcConfigurer() {
@Override
public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(new GuiguMessageConverter());
}
}
}
}
/**
* 自定义的Converter
*/
public class GuiguMessageConverter implements HttpMessageConverter<Person> {
@Override
public boolean canRead(Class<?> clazz, MediaType mediaType) {
return false;
}
@Override
public boolean canWrite(Class<?> clazz, MediaType mediaType) {
return clazz.isAssignableFrom(Person.class);
}
/**
* 服务器要统计所有MessageConverter都能写出哪些内容类型
*
* application/x-guigu
* @return
*/
@Override
public List<MediaType> getSupportedMediaTypes() {
return MediaType.parseMediaTypes("application/x-guigu");
}
@Override
public Person read(Class<? extends Person> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
return null;
}
@Override
public void write(Person person, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
//自定义协议数据的写出
String data = person.getUserName()+";"+person.getAge()+";"+person.getBirth();
//写出去
OutputStream body = outputMessage.getBody();
body.write(data.getBytes());
}
}
import java.util.Date;
@Controller
public class ResponseTestController {
/**
* 1、浏览器发请求直接返回 xml [application/xml] jacksonXmlConverter
* 2、如果是ajax请求 返回 json [application/json] jacksonJsonConverter
* 3、如果硅谷app发请求，返回自定义协议数据 [appliaction/x-guigu] xxxxConverter
* 属性值1;属性值2;
*
* 步骤：
* 1、添加自定义的MessageConverter进系统底层
* 2、系统底层就会统计出所有MessageConverter能操作哪些类型
* 3、客户端内容协商 [guigu--->guigu]
*
* 作业：如何以参数的方式进行内容协商
* @return
*/
@ResponseBody //利用返回值处理器里面的消息转换器进行处理
@GetMapping(value = "/test/person")
public Person getPerson(){
Person person = new Person();
person.setAge(28);
person.setBirth(new Date());
person.setUserName("zhangsan");
return person;
}
}
用Postman发送/test/person（请求头Accept:application/x-guigu)，将返回自定义协议数据的写出。
42、响应处理-【源码分析】-浏览器与PostMan内容协商完全适配
假设你想基于自定义请求参数的自定义内容协商功能。
换句话，在地址栏输入http://localhost:8080/test/person?format=gg返回数据，跟http://localhost:8080/test/person且请求头参数Accept:application/x-guigu的返回自定义协议数据的一致。
@Configuration(proxyBeanMethods = false)
public class WebConfig /*implements WebMvcConfigurer*/ {
//1、WebMvcConfigurer定制化SpringMVC的功能
@Bean
public WebMvcConfigurer webMvcConfigurer(){
return new WebMvcConfigurer() {
/**
* 自定义内容协商策略
* @param configurer
*/
@Override
public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
//Map<String, MediaType> mediaTypes
Map<String, MediaType> mediaTypes = new HashMap<>();
mediaTypes.put("json",MediaType.APPLICATION_JSON);
mediaTypes.put("xml",MediaType.APPLICATION_XML);
//自定义媒体类型
mediaTypes.put("gg",MediaType.parseMediaType("application/x-guigu"));
//指定支持解析哪些参数对应的哪些媒体类型
ParameterContentNegotiationStrategy parameterStrategy = new ParameterContentNegotiationStrategy(mediaTypes);
// parameterStrategy.setParameterName("ff");
//还需添加请求头处理策略，否则accept:application/json、application/xml则会失效
HeaderContentNegotiationStrategy headeStrategy = new HeaderContentNegotiationStrategy();
configurer.strategies(Arrays.asList(parameterStrategy, headeStrategy));
}
}
}
...
}
日后开发要注意，有可能我们添加的自定义的功能会覆盖默认很多功能，导致一些默认的功能失效。
43、视图解析-Thymeleaf初体验
Thymeleaf is a modern server-side Java template engine for both web and standalone environments.
Thymeleaf's main goal is to bring elegant natural templates to your development workflow — HTML that can be correctly displayed in browsers and also work as static prototypes, allowing for stronger collaboration in development teams.
With modules for Spring Framework, a host of integrations with your favourite tools, and the ability to plug in your own functionality, Thymeleaf is ideal for modern-day HTML5 JVM web development — although there is much more it can do.——Link
thymeleaf使用
引入Starter
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
自动配置好了thymeleaf
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(ThymeleafProperties.class)
@ConditionalOnClass({
TemplateMode.class, SpringTemplateEngine.class })
@AutoConfigureAfter({
WebMvcAutoConfiguration.class, WebFluxAutoConfiguration.class })
public class ThymeleafAutoConfiguration {
...
}
自动配好的策略
所有thymeleaf的配置值都在 ThymeleafProperties
配置好了 SpringTemplateEngine
配好了 ThymeleafViewResolver
我们只需要直接开发页面
public static final String DEFAULT_PREFIX = "classpath:/templates/";//模板放置处
public static final String DEFAULT_SUFFIX = ".html";//文件的后缀名
编写一个控制层：
@Controller
public class ViewTestController {
@GetMapping("/hello")
public String hello(Model model){
//model中的数据会被放在请求域中 request.setAttribute("a",aa)
model.addAttribute("msg","一定要大力发展工业文化");
model.addAttribute("link","http://www.baidu.com");
return "success";
}
}
/templates/success.html：
<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<h1 th:text="${msg}">nice</h1>
<h2>
<a href="www.baidu.com" th:href="${link}">去百度</a> <br/>
<a href="www.google.com" th:href="@{/link}">去百度</a>
</h2>
</body>
</html>
server:
servlet:
context-path: /app #设置应用名
这个设置后，URL要插入/app, 如http://localhost:8080/app/hello.html。
基本语法
表达式
| 表达式名字 | 语法 | 用途 |
|---|---|---|
| 变量取值 | ${...} | 获取请求域、session域、对象等值 |
| 选择变量 | *{...} | 获取上下文对象值 |
| 消息 | #{...} | 获取国际化等值 |
| 链接 | @{...} | 生成链接 |
| 片段表达式 | ~{...} | jsp:include 作用，引入公共页面片段 |
字面量
- 文本值: 'one text' , 'Another one!' ,…
- 数字: 0 , 34 , 3.0 , 12.3 ,…
- 布尔值: true , false
- 空值: null
- 变量： one，two，.... 变量不能有空格
文本操作
- 字符串拼接: +
- 变量替换: |The name is ${name}|
数学运算
- 运算符: + , - , * , / , %
布尔运算
- 运算符: and , or
- 一元运算: ! , not
比较运算
- 比较: > , < , >= , <= ( gt , lt , ge , le )
- 等式: == , != ( eq , ne )
条件运算
- If-then: (if) ? (then)
- If-then-else: (if) ? (then) : (else)
- Default: (value) ?: (defaultvalue)
特殊操作
- 无操作： _
设置属性值-th:attr
- 设置单个值
<form action="subscribe.html" th:attr="action=@{/subscribe}">
<fieldset>
<input type="text" name="email" />
<input type="submit" value="Subscribe!" th:attr="value=#{subscribe.submit}"/>
</fieldset>
</form>
- 设置多个值
<img src="../../images/gtvglogo.png"
th:attr="src=@{/images/gtvglogo.png},title=#{logo},alt=#{logo}" />
官方文档 - 5 Setting Attribute Values
迭代
<tr th:each="prod : ${prods}">
<td th:text="${prod.name}">Onions</td>
<td th:text="${prod.price}">2.41</td>
<td th:text="${prod.inStock}? #{true} : #{false}">yes</td>
</tr>
<tr th:each="prod,iterStat : ${prods}" th:class="${iterStat.odd}? 'odd'">
<td th:text="${prod.name}">Onions</td>
<td th:text="${prod.price}">2.41</td>
<td th:text="${prod.inStock}? #{true} : #{false}">yes</td>
</tr>
条件运算
<a href="comments.html"
th:href="@{/product/comments(prodId=${prod.id})}"
th:if="${not #lists.isEmpty(prod.comments)}">view</a>
<div th:switch="${user.role}">
<p th:case="'admin'">User is an administrator</p>
<p th:case="#{roles.manager}">User is a manager</p>
<p th:case="*">User is some other thing</p>
</div>
属性优先级
| Order | Feature | Attributes |
|---|---|---|
| 1 | Fragment inclusion | th:insert th:replace |
| 2 | Fragment iteration | th:each |
| 3 | Conditional evaluation | th:if th:unless th:switch th:case |
| 4 | Local variable definition | th:object th:with |
| 5 | General attribute modification | th:attr th:attrprepend th:attrappend |
| 6 | Specific attribute modification | th:value th:href th:src ... |
| 7 | Text (tag body modification) | th:text th:utext |
| 8 | Fragment specification | th:fragment |
| 9 | Fragment removal | th:remove |
官方文档 - 10 Attribute Precedence
44、web实验-后台管理系统基本功能
项目创建
使用IDEA的Spring Initializr。
- thymeleaf、
- web-starter、
- devtools、
- lombok
登陆页面
/static放置 css，js等静态资源/templates/login.html登录页
<html lang="en" xmlns:th="http://www.thymeleaf.org"><!-- 要加这玩意thymeleaf才能用 -->
<form class="form-signin" action="index.html" method="post" th:action="@{/login}">
...
<!-- 消息提醒 -->
<label style="color: red" th:text="${msg}"></label>
<input type="text" name="userName" class="form-control" placeholder="User ID" autofocus>
<input type="password" name="password" class="form-control" placeholder="Password">
<button class="btn btn-lg btn-login btn-block" type="submit">
<i class="fa fa-check"></i>
</button>
...
</form>
/templates/main.html主页
thymeleaf内联写法：
<p>Hello, [[${session.user.name}]]!</p>
登录控制层
@Controller
public class IndexController {
/**
* 来登录页
* @return
*/
@GetMapping(value = {
"/","/login"})
public String loginPage(){
return "login";
}
@PostMapping("/login")
public String main(User user, HttpSession session, Model model){
//RedirectAttributes
if(StringUtils.hasLength(user.getUserName()) && "123456".equals(user.getPassword())){
//把登陆成功的用户保存起来
session.setAttribute("loginUser",user);
//登录成功重定向到main.html; 重定向防止表单重复提交
return "redirect:/main.html";
}else {
model.addAttribute("msg","账号密码错误");
//回到登录页面
return "login";
}
}
/**
* 去main页面
* @return
*/
@GetMapping("/main.html")
public String mainPage(HttpSession session, Model model){
//最好用拦截器,过滤器
Object loginUser = session.getAttribute("loginUser");
if(loginUser != null){
return "main";
}else {
//session过期，没有登陆过
//回到登录页面
model.addAttribute("msg","请重新登录");
return "login";
}
}
}
模型
@AllArgsConstructor
@NoArgsConstructor
@Data
public class User {
private String userName;
private String password;
}
