rest

REST

HTTP状态码

• org.springframework.http.HttpStatus

  public enum HttpStatus {
  	OK(200, "OK"),
  	NOT_FOUND(404, "Not Found"),
  	BAD_REQUEST(400, "Bad Request"),
  	...
  
  }
  

响应

• 响应头

  • 元信息 org.springframework.http.HttpHeaders

    public class HttpHeaders implements MultiValueMap<String, String>, Serializable {
    	public static final String ACCEPT = "Accept";
    	public static final String ACCEPT_CHARSET = "Accept-Charset";
    	public static final String ACCEPT_ENCODING = "Accept-Encoding";
    	...
    }

    • 下列是一个响应头部分信息

    accept-ranges: bytes
    access-control-allow-methods: GET
    access-control-allow-origin: *
    access-control-max-age: 3600
    age: 3058
    content-encoding: gzip
    content-length: 88320
    

• 响应体

  • 业务信息
  • Http实体 org.springframework.http.HttpEntity

@RestController
public class Controller {

    @GetMapping("/")
    public ResponseEntity<String> helloWorld() {
        return ResponseEntity.ok("hello");
    }

}

URI & URL

• URI—Uniform Resource Identifier通用资源标志符 Web上可用的每种资源如HTML文档、图像、视频片段、程序等都是一个来URI来定位的 URI一般由三部组成

  1. 访问资源的命名机制
  2. 存放资源的主机名
  3. 资源自身的名称，由路径表示，着重强调于资源。

• URL—Uniform Resource Location统一资源定位符

  URL是Internet上用来描述信息资源的字符串，主要用在各种WWW客户程序和服务器程序上，特别是著名的Mosaic。采用URL可以用一种统一的格式来描述各种信息资源，包括文件、服务器的地址和目录等。URL一般由三部组成

  1. 协议(或称为服务方式)
  2. 存有该资源的主机IP地址(有时也包括端口号)
  3. 主机资源的具体地址。如目录和文件名等

@RequestMapping

• @RequestMapping

  • @GetMapping

    @RequestMapping(method = RequestMethod.GET)
    public @interface GetMapping {
       	@AliasFor(annotation = RequestMapping.class)
    	String name() default "";
        ...
    }

  • @PutMapping

    @RequestMapping(method = RequestMethod.PUT)
    public @interface PutMapping {
        @AliasFor(annotation = RequestMapping.class)
    	String name() default "";
    }

  • @PostMapping

    @RequestMapping(method = RequestMethod.POST)
    public @interface PostMapping {
        @AliasFor(annotation = RequestMapping.class)
    	String name() default "";
    }

  • @DeleteMapping

    @RequestMapping(method = RequestMethod.DELETE)
    public @interface DeleteMapping {
        @AliasFor(annotation = RequestMapping.class)
    	String name() default "";
    }

• spring 4.2 以后开始引入 语义强的 几个Mapping 如上所示。从源码查看上来说 这几个注解都覆盖了原始的@RequestMapping 注解 。

• ~~@AliasFor 别名语义，委派到具体的注解中 ，在@GetMapping中 将传入name值发送给 @RequestMapping的name~~

• @AliasFor

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.TYPE})
@Documented
public @interface F1 {

    String value() default "";
    String method() default "";
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@F1(method = "GET")
public @interface F2 {

    @AliasFor(annotation = F1.class)
    String value() default "";


}

public class T {

    @F2(value = "李四")
    private static void method2() {

    }

}

public class Run {

    public static void main(String[] args) throws Exception {
        Class<T> tClass = T.class;
        Method method2 = tClass.getDeclaredMethod("method2");
        F2 annotation = method2.getAnnotation(F2.class);

        Consumer<F2> logic = new Consumer<F2>() {
            @Override
            public void accept(F2 f2a) {
                String value = f2a.value();
                System.out.println(value);
            }
        };

        F2 af2 = AnnotationUtils
                .findAnnotation(method2, F2.class);
        logic.accept(af2);

    }

}

• 在af2变量中它存放了 @F1#method的数据

---

RestTemplate

• org.springframework.web.client.RestTemplate

public RestTemplate() {
   this.messageConverters.add(new ByteArrayHttpMessageConverter());
   this.messageConverters.add(new StringHttpMessageConverter());
   this.messageConverters.add(new ResourceHttpMessageConverter(false));
//...
}

构造方法中加入了很多 HttpMessageConverter实现类

• HttpMessageConverter

public interface HttpMessageConverter<T> {

  boolean canRead(Class<?> clazz, @Nullable MediaType mediaType);

  boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType);

    List<MediaType> getSupportedMediaTypes();

  T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
         throws IOException, HttpMessageNotReadableException;

  void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage)
         throws IOException, HttpMessageNotWritableException;

}

流程

请求发送 -> canRead: 发送一个请求
canRead -> read: 经过判断是否能够继续操作，通过HttpInputMessage获取
read -> java对象: 转换成java对象
java对象 -> write: 经过canwrite判断，通过HttpOutputMessage返回

• 以String 为例，相关转换器 org.springframework.http.converter.StringHttpMessageConverter

  

@PostMapping(value="/string")
public String readString(@RequestBody String string) {
    return "测试数据" + string + "'";
}

• 发送http://localhost:3919/string 参数为

  {
    "value": [
      "Z"
    ],
    "hash": 1,
    "serialVersionUID": 1
  }

  1. org.springframework.http.converter.AbstractHttpMessageConverter#read这个步骤还没有到return 返回

     @Override
     public final T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
           throws IOException, HttpMessageNotReadableException {
     
        return readInternal(clazz, inputMessage);
     }
     
     // org.springframework.http.converter.StringHttpMessageConverter#readInternal
     	@Override
     	protected String readInternal(Class<? extends String> clazz, HttpInputMessage inputMessage) throws IOException {
     		Charset charset = getContentTypeCharset(inputMessage.getHeaders().getContentType());
     		return StreamUtils.copyToString(inputMessage.getBody(), charset);
     	}

     

  2. 将body赋值

     @Override
     public InputStream getBody() {
        return (this.body != null ? this.body : StreamUtils.emptyInput());
     }

  3. 执行到return 后 进入org.springframework.http.converter.AbstractHttpMessageConverter#write