前言

主要介绍RestTemplate的原理以及使用等

1. 简介

常见的http客户端请求工具：

• jdk HttpURLConnection
• Apache HttpClient 比较常用
• OkHttp 比较常用

RestTemplate是一个同步的web http客户端请求模板工具
是基于spring框架的底层的一个知识点

具体常用的方法如官网所示
RestTemplate官方文档

部分常用方法截图如下：

具体的构造方法如下：

RestTemplate默认是使用HttpURLConnection，可以通过构造方法替换底层的执行引擎，常见的引擎又HttpClient、Netty、OkHttp
如果要想替换直接如构造方法所示即可

//底层执行引擎
RestTemplate template=new RestTemplate();

//底层执行引擎ClientHttp
RestTemplate template=new RestTemplate(ClientHttpRequestFactory requestFactory);

2. http状态码

1. 消息

▪ ==100 Continue== 通知继续
▪ 101 Switching Protocols
▪ 102 Processing

1. 成功

▪ ==200 OK==
▪ 201 Created
▪ 202 Accepted
▪ 203 Non-Authoritative Information
▪ 204 No Content
▪ 205 Reset Content
▪ 206 Partial Content
▪ 207 Multi-Status

1. 重定向

▪ 300 Multiple Choices
▪ ==301 Moved Permanently== 永久迁移
▪ ==302 Move Temporarily== 临时迁移
▪ 303 See Other
▪ 304 Not Modified
▪ 305 Use Proxy
▪ 306 Switch Proxy
▪ 307 Temporary Redirect

1. 请求错误 (客户端异常)

▪ 400 Bad Request
▪ 401 Unauthorized
▪ 402 Payment Required
▪ 403 Forbidden
▪ ==404 Not Found==
▪ 405 Method Not Allowed
▪ 406 Not Acceptable
▪ 407 Proxy Authentication Required
▪ 408 Request Timeout
▪ 409 Conflict
▪ 410 Gone
▪ 411 Length Required
▪ 412 Precondition Failed
▪ 413 Request Entity Too Large
▪ 414 Request-URI Too Long
▪ 415 Unsupported Media Type
▪ 416 Requested Range Not Satisfiable
▪ 417 Expectation Failed
▪ 418 I'm a teapot
▪ 421Misdirected Request
▪ 422 Unprocessable Entity
▪ 423 Locked
▪ 424 Failed Dependency
▪ 425 Too Early
▪ 426 Upgrade Required
▪ 449 Retry With
▪ 451 Unavailable For Legal Reasons

1. 服务器错误

▪ 500 Internal Server Error
▪ 501 Not Implemented
▪ 502 Bad Gateway
▪ 503 Service Unavailable
▪ 504 Gateway Timeout
▪ 505 HTTP Version Not Supported
▪ 506 Variant Also Negotiates
▪ 507 Insufficient Storage
▪ 509 Bandwidth Limit Exceeded
▪ 510 Not Extended
▪ 600 Unparseable Response Headers

3. get请求

其业务逻辑层面如下所示

@RestController

public class UserController {
    
    @GetMapping("/addUser/{#userId}/{userName}")
    public UserDTO addUser(@PathVariable("userId") Long userId,
                            @PathVariable("userName") Long userName){
        UserDTO userDTO =new UserDTO();
        userDTO.setUserId(userId);
        userDTO.setUserName(userName);
        return UserDTO;
    }
}

• getForObject()：返回对象为响应体中数据转化成的对象，基本上可以理解为Json

public class RestController {

    @Resource
    RestTemplate restTemplate;
    
    private static final String url = "http://localhost:8080/addUser/8888/码农研究僧";

    @GetMapping("/getForObject")
    public Object getForObject(){
        Map<String ,Long >paramMap =new HashMap<>();
        UserDTO result ==restTemplate.getForObject(url,UserDTO.class,paramMap);
        //Map<String ,Long > result =restTemplate.getForObject(url,Map.class,paramMap);
        return result;
    }
}

之后访问页面http://localhost:8080/getForObject即可显示其信息

• getForEntity()：返回对象为ResponseEntity对象，包含了响应中的一些重要信息，比如响应头、响应状态码、响应体等

具体代码模块如下

 @GetMapping("/getForEntity")
  public Object getForEntity(){
    Map<String ,Long >paramMap =new HashMap<>();
    
    //ResponseEntity包装返回结果
    ResponseEntity <HashMap> responseEntity =restTemplate.getForEntity(url,HashMap.class,paramMap);
    
    //返回状态码包装类
    HttpStatus statusCode =responseEntity.getStatusCode();
    
    //返回状态码
    int StatusCodeValue=responseEntity.getStatusCodeValue();
    
    //http返回头
    HttpHeaders headers=responseEntity.getHeaders();
    
    //返回对应请求结果
    return responseEntity.getBody();

4. post请求

post与get的区别在于post的方法传参map必须是MultiValueMap

基本类型传参和实体类型传参

//http://localhost:8080/postFor0bject1
@GetMapping("/postForObject1")
public UserDT0 postForObject1 ( ) {
    //远程访问的Url UserDTO
    String url = "http://localhost:8080/addUser1";
    // Post方法必须使用MultiValueMap传参。//使用UserDTO传参也可以
    
    MultiValueMap<String，0bject> paramMap = new LinkedMultiValueMap<>();
    paramMap.add ("userId", 1008L);
    paramMap.add ("userName "，"巧克力");
    UserDT0 userDTO = restTemplate.postForObject(url,paramMap，UserDT0.class);
    return userDTO;
}

如果使用到@RequestMapping,用httpentity

@RequestMapping( value = "/addUser3" )
public UserDT0 addUser3(@RequestBody UserDT0 userDTO) {
    userDTo.setUserName(userDTo.getUserName() + " from RequestBody" );
    return userDTO;
}

//http://localhost:8888/postForObject2
@GetMapping("/postForObject2")
public UserDT0 postForObject2( ) {
    //申明一个请求头
    HttpHeaders headers = new HttpHeaders();
    //application/json
    headers.setContentType( MediaType .APPLICATION_JSON);//远程访问的Url UserDTO
    string url = "http://localhost:8080/addUser3";
    /**
        此处使用MultiValueMap会报错
        MultiValueMap<String，0bject> paramMap = new LinkedMultiValueMap<>( );
        paramMap.add("userId",100OL) ;
        paramMap.add("userName","fencaibc");*/
    //此处可以使用HashMap代替，但是会有警告
    
    UserDT0 userDTO = new UserDTO( );
    userDTO.setUserId( 1088L);
    userDT0.setUserName("课程");
    HttpEntity<UserDTO> entityParam new HttpEntity<UserDTO>(userDTO，headers) ;
    UserDT0 result = restTemplate.postFor0bject(url, entityParam，UserDTO.class);
    return result ;
}

其他类似

//http://localhost:8088/ postForEntity1@GetMapping( " / postForEntity1")
public UserDT0 postForEntity1( ) {
    string url = "http://localhost:8080/addUser1" ;
    
    MultiValueMap<String，object> paramMap = new LinkedMultiValueMap<>( );
    
    paramMap.add("userId", 100);
    paramMap.add("userName" ，"课程");
    
    ResponseEntity<UserDT0> userDTOResponseEntity =restTemplate.postForEntity(url,paramMap，UserDTO.class) ;
    
    HttpStatus statusCode = userDTOResponseEntity.getStatusCode( );
    
    int statusCodeValue = userDTOResponseEntity.getStatusCodeValue( );
    
    HttpHeaders headers = userDTOResponseEntity. getHeaders( );
    
    return userDTOResponseEntity. getBody( );
}

5. Exchange

可以用get也可以用post

// http://localhost:8088/exchange@GetMapping("/ exchange" )
public UserDT0 exchange( ) {
    //访问的远程地址UserDTO
    String url= "http:// localhost:8080 addUser1" ;
    //传参使用MultiValueMap
    MultiValueMap<String，0bject> paramMap = new LinkedMultiValueMap<>();
    paramMap.add("userId",100);
    paramMap.add("userName "，"exchange" );
    //HttpEntity包装了传参
    HttpEntity<MultiValueMap> requestEntity = new HttpEntity<>(paramMap ) ;
    ResponseEntity<UserDTO> response =
    restTemplate.exchange(url，HttpMethod.POST，requestEntity，UserDT0.class) ;
    return response.getBody ( );
}