@PathVariable @RequestParam @RequestBody @ModelAttribute的区别及RestTemplate调用方式

@PathVariable

• 能匹配url模板中的占位符对应参数
• 支持get和post请求
• Controller声明：

//get-uri: localhost:8080/test/pathVariable/123
@GetMapping(value = "pathVariable/{param}")
public String getPathVariable(@PathVariable("param") String id) {
    return id;
}

//post-uri: localhost:8080/test/pathVariable/123
@PostMapping(value = "pathVariable/{param}")
public String postPathVariable(@PathVariable("param") String id) {
    return id;
}
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• RestTemplate访问：

public static void pathVariable() {
    Map<String, String> map = new HashMap<>();
    map.put("paramName", "name1");
    RestTemplate restTemplate = new RestTemplate();
    //get调用使用getForEntity
    ResponseEntity<String> responseEntity = restTemplate.getForEntity(host+"/test/pathVariable/{paramName}", String.class, map);
    //post须要用postForEntity方法调用
    //ResponseEntity<String> responseEntity = restTemplate.postForEntity(host+"/test/pathVariable/{paramName}", null, String.class, map);
    System.out.println("getPathVariable2: " + responseEntity.getBody());//输出“name1”
}
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@RequestParam

• 与PathVariable相似，RequestParam只能用于url参数传值，可传入简单类型、指定映射参数名、指定是否必填、设置默认值等
• 支持get和post请求
• Controller声明：

//get-uri: localhost:8080/test/requestParam?param=xxx
@GetMapping(value = "test/requestParam")
public String getRequestParam(@RequestParam(defaultValue = "ssss") String param) {
//当请求url为localhost:8080/test/requestParam时，param为默认值ssss
    
//post-uri: localhost:8080/test/requestParam?param=xxx
@PostMapping(value = "test/requestParam")
public String getRequestParam(@RequestParam(name = "aa", required = false) String param) {
//指定参数为“aa”，即当url为localhost:8080/test/requestParam?aa=p1时，param为p1
//当url为localhost:8080/test/requestParam时，param为null

//post-uri: localhost:8080/test/requestParam
@PostMapping(value = "test/requestParam")
public String postRequestParam(@RequestParam(required = false) int param) {
// int是基本类型，即便设置required=false，由于int没法设置为null仍然会报错，能够将int替换为Integer
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• RestTemplate访问：

public static void requestParam() {
    RestTemplate restTemplate = new RestTemplate();
    ResponseEntity<String> responseEntity = restTemplate.getForEntity(host+"/test/requestParam",
            String.class);
    System.out.println("getRequestParam: " + responseEntity.getBody());//url未指定，默认值为ssss
    
    Map<String, String> map = new HashMap<>();
    map.put("param", "name3");
    responseEntity = restTemplate.getForEntity(host+"/test/requestParam?param={param}", String.class);
    System.out.println("getRequestParam: " + responseEntity.getBody());//输出name3
}

public static void requestParam2() {
    RestTemplate restTemplate = new RestTemplate();
    ResponseEntity<String> responseEntity = restTemplate.postForEntity(host+"/test/requestParam",
            String.class);
    System.out.println("postRequestParam: " + responseEntity.getBody());//未指定aa，输出结果为null
}
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@RequestBody

• RequestBody主要经过请求体body传值，经常使用来处理content-type=application/json请求，同时支持get和post请求，能获取到body中的数据并转化为对象
• 支持get和post请求
• Controller声明：

//get-uri: localhost:8080/test/requestBody
@GetMapping(value = "test/requestBody")
public BaseParam getRequestBody(@RequestBody BaseParam param) {
    return param;
}

//post-uri: localhost:8080/test/requestBody
@PostMapping(value = "test/requestBody")
public BaseParam postRequestBody(@RequestBody BaseParam param) {
    return param;
}
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• RestTemplate访问：

//get请求
//RestTemplate的get请求不支持设置body，因此使用restTemplate没法调用get请求的@RequestBody注解，但使用PostMan等工具是能够发送带body的get请求的

//post请求
public static void postRequestBody() {
    HttpHeaders requestHeaders = new HttpHeaders();
    //注意设置content-type
    requestHeaders.add("Content-type", MediaType.APPLICATION_JSON_VALUE);
    BaseParam param = new BaseParam();
    param.setParamName("name4");
    HttpEntity<BaseParam> requestEntity = new HttpEntity<>(param, requestHeaders);
    RestTemplate restTemplate = new RestTemplate();
    ResponseEntity<BaseParam> responseEntity = restTemplate.postForEntity(host+"/test/requestBody",
            requestEntity, BaseParam.class);
    System.out.println("postRequestBody: " + responseEntity.getBody().getParamName());//输出name4
}

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@ModelAttribute

• ModelAttribute注解参数时，发送请求的content-type须要为"x-www-form-urlencoded"
• 仅支持post请求且content-type=x-www-form-urlencoded能接收到数据；若是是post请求且content-type=application/json、get请求且content-type=x-www-form-urlencoded、get请求且content-type=application/json均不会报错但没法接收到数据
• Controller声明：

@PostMapping(value = "test/modelAttribute")
public String postModelAttribute(@ModelAttribute BaseParam param) {
    return param.getParamName();
}
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• RestTemplate访问：

public static void postModelAttribute() {
    HttpHeaders requestHeaders = new HttpHeaders();
    requestHeaders.add("Content-type", MediaType.APPLICATION_FORM_URLENCODED_VALUE);
    MultiValueMap<String, String> params= new LinkedMultiValueMap<String, String>();
    params.add("account", "用户名");
    params.add("paramName", "123456");
    HttpEntity<MultiValueMap<String, String>> requestEntity = new HttpEntity<>(params, requestHeaders);
    RestTemplate restTemplate = new RestTemplate();
    //须要提供自定义convert
    restTemplate.getMessageConverters().add(new TestMappingJackson2HttpMessageConverter());
    ResponseEntity<String> responseEntity = restTemplate.postForEntity(host+"/test/modelAttribute",
            requestEntity, String.class);
    System.out.println("postModelAttribute: " + responseEntity.getBody());//输出123456
}
    
//自定义convert
public class TestMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {
    public TestMappingJackson2HttpMessageConverter() {
        List<MediaType> mediaTypes = new ArrayList<>();
        mediaTypes.add(MediaType.TEXT_PLAIN);
        //添加form-urlencoded类型转换
        mediaTypes.add(MediaType.APPLICATION_FORM_URLENCODED);
        setSupportedMediaTypes(mediaTypes);
    }
}
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以上对@PathVariable、@RequestParam、@RequestBody、@ModelAttribute的使用方式及RestTemplate如何调用相应注解接口作了总结，若有不对欢迎指出，谢谢！

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