Springboot学习03-SpringMVC自动配置

• Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.
• Support for serving static resources, including support for WebJars (covered later in this document)).
• Automatic registration of Converter, GenericConverter, and Formatter beans.
• Support for HttpMessageConverters (covered later in this document).
• Automatic registration of MessageCodesResolver (covered later in this document).
• Static index.html support.
• Custom Favicon support (covered later in this document).
• Automatic use of a ConfigurableWebBindingInitializer bean (covered later in this document).

public class WebMvcAutoConfiguration {
//-在Springboot启动初始化时，自动装载WebMvcAutoConfiguration类，
//其中包括WebMvcAutoConfiguration内部类WebMvcAutoConfigurationAdapter下的ContentNegotiatingViewResolver viewResolver（）方法
public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ResourceLoaderAware { @Bean
@ConditionalOnBean({ViewResolver.class})
@ConditionalOnMissingBean(
name = {"viewResolver"},
value = {ContentNegotiatingViewResolver.class}
)
public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
resolver.setContentNegotiationManager((ContentNegotiationManager)beanFactory.getBean(ContentNegotiationManager.class));
resolver.setOrder(-2147483648);
return resolver;
} }
}

public class ContentNegotiatingViewResolver extends WebApplicationObjectSupport implements ViewResolver, Ordered, InitializingBean {
//2-ContentNegotiatingViewResolver 执行其内部initServletContext()初始化方法，从BeanFactoryUtils中获取全部ViewResolver
protected void initServletContext(ServletContext servletContext) {
Collection<ViewResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(this.obtainApplicationContext(), ViewResolver.class).values();
ViewResolver viewResolver;
if (this.viewResolvers == null) { Iterator var3 = matchingBeans.iterator();
while(var3.hasNext()) {
viewResolver = (ViewResolver)var3.next();
if (this != viewResolver) {
this.viewResolvers.add(viewResolver);
}
}
}
…………………………省略
} //2-当一个请求进来时，调用ContentNegotiatingViewResolver 下的View resolveViewName()方法，，并返回bestView，主要包括beanName参数，即对应渲染的(比如：html)文件名称
@Nullable
public View resolveViewName(String viewName, Locale locale) throws Exception {
//ContentNegotiatingViewResolver 根据文件名和请求头类型来决定返回什么样的View。而mediaTypes这个属性存储了 你请求后缀名 或者 参数 所对应 的mediaType
RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
List<MediaType> requestedMediaTypes = this.getMediaTypes(((ServletRequestAttributes)attrs).getRequest());
if (requestedMediaTypes != null) {
//获取候选视图对象
List<View> candidateViews = this.getCandidateViews(viewName, locale, requestedMediaTypes);
//选择一个最适合的视图对象
View bestView = this.getBestView(candidateViews, requestedMediaTypes, attrs);
if (bestView != null) {
//返回视图对象
return bestView;
}
}
……………省略
} //2-1-获取候选视图对象
private List<View> getCandidateViews(String viewName, Locale locale, List<MediaType> requestedMediaTypes) throws Exception {
List<View> candidateViews = new ArrayList();
if (this.viewResolvers != null) {
//获取全部视图解析器
Iterator var5 = this.viewResolvers.iterator();
//筛选出候选View
while(var5.hasNext()) {
…………………………省略
while(var11.hasNext()) {
String extension = (String)var11.next();
String viewNameWithExtension = viewName + '.' + extension;
view = viewResolver.resolveViewName(viewNameWithExtension, locale);
if (view != null) {
candidateViews.add(view);//获取view
}
}
} }
return candidateViews;
}
}

@SpringBootApplication
public class SpringbootdemoApplication { public static void main(String[] args) {
SpringApplication.run(SpringbootdemoApplication.class, args);
} //在Springboot启动时，加载自定义的MyViewResolver类
@Bean
public ViewResolver myViewResolver(){
return new MyViewResolver();
} //(这里为了方便，在启动类下写了一个内部类)
//MyViewResolver实现接口类ViewResolver
private static class MyViewResolver implements ViewResolver{ @Override
public View resolveViewName(String s, Locale locale) throws Exception {
return null;
}
}}

//1-controller层
@Controller
public class DemoController {
Logger log = LoggerFactory.getLogger(DemoController.class); @RequestMapping(value="get/student")
public String getStudent(Student student,Model model){
log.debug("student: " + student);
model.addAttribute("student",student);
return "student";
}}
//2-自定义converter
@Configuration
public class StringToStudentConverrter implements Converter<String,Student> {
@Override
public Student convert(String s) {
//student=tyj-18
String[] split = s.split("-");
Student student = new Student(split[0],Integer.parseInt(split[1]));
return student;
}
}

//3-html示例
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div th:text="${student.name}"></div>
<div th:text="${student.age}"></div>
<strong>success!</strong>
</body>
</html>

//1-自定义HttpMessageConverters
public class MyMessageConveter extends AbstractHttpMessageConverter<Student>{ public MyMessageConveter() {
//Content-Type= application/xxx-tyj
super(new MediaType("application", "xxx-tyj", Charset.forName("UTF-8")));
} @Override
protected boolean supports(Class<?> aClass) {
// 表明只处理UserEntity类型的参数。
return Student.class.isAssignableFrom(aClass);
} //重写readlntenal 方法，处理请求的数据。代码表明我们处理由“-”隔开的数据，并转成 Student类型的对象。
@Override
protected Student readInternal(Class<? extends Student> aClass, HttpInputMessage httpInputMessage)
throws IOException, HttpMessageNotReadableException {
String content = StreamUtils.copyToString(httpInputMessage.getBody(), Charset.forName("UTF-8"));
String[] split = content.split("-");
return new Student(split[0],Integer.parseInt(split[1]));
} //重写writeInternal ，处理如何输出数据到response。
@Override
protected void writeInternal(Student student, HttpOutputMessage httpOutputMessage)
throws IOException, HttpMessageNotWritableException {
String out = "hello: " +student.getName() + " ,你今年" + student.getAge() + "了么？";
httpOutputMessage.getBody().write(out.getBytes());
}
}

//2-加载自定义的MyMessageConveter
@Configuration
public class MySpringBootConfig {
@Bean
public MyMessageConveter MyMessageConveter (){
return new MyMessageConveter();
}
}

//3-controller
@Controller
public class DemoController { @RequestMapping(value="hello/student",method = POST)
@ResponseBody
public Student helloStudent(@RequestBody Student student){
return student;
}}

接口测试
URL：POST localhost:8080/hello/student
header: Content-Type = application/xxx-tyj
body: tyj-21返回值：hello: tyj ,你今年21了么？

@Configuration
public class MyWebMvcConfigurerAdapter extends WebMvcConfigurerAdapter {
// 添加converter的第一种方式，代码很简单，也是推荐的方式
// 这样做springboot会把我们自定义的converter放在顺序上的最高优先级（List的头部）
// 即有多个converter都满足Accpet/ContentType/MediaType的规则时，优先使用我们这个
@Bean
public MyMessageConveter MyMessageConveter (){
return new MyMessageConveter();
}
// 添加converter的第二种方式
// 通常在只有一个自定义WebMvcConfigurerAdapter时，会把这个方法里面添加的converter(s)依次放在最高优先级（List的头部）
// 虽然第一种方式的代码先执行，但是bean的添加比这种方式晚，所以方式二的优先级 大于 方式一
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
// add方法可以指定顺序，有多个自定义的WebMvcConfigurerAdapter时，可以改变相互之间的顺序
// 但是都在springmvc内置的converter前面
converters.add(new MyMessageConveter());
} // 添加converter的第三种方式
// 同一个WebMvcConfigurerAdapter中的configureMessageConverters方法先于extendMessageConverters方法执行
// 可以理解为是三种方式中最后执行的一种，不过这里可以通过add指定顺序来调整优先级，也可以使用remove/clear来删除converter，功能强大
// 使用converters.add(xxx)会放在最低优先级（List的尾部）
// 使用converters.add(0,xxx)会放在最高优先级（List的头部）
@Override
public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(new MyMessageConveter());
}
}