@PathVariable @RequestParam @RequestBody @ModelAttribute的區別及RestTemplate調用方式

@PathVariable

• 能匹配url模板中的佔位符對應參數
• 支持get和post請求
• Controller聲明：

//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訪問：

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

• 與PathVariable相似，RequestParam只能用於url參數傳值，可傳入簡單類型、指定映射參數名、指定是否必填、設置默認值等
• 支持get和post請求
• Controller聲明：

//get-uri: localhost:8080/test/requestParam?param=xxx
@GetMapping(value = "test/requestParam")
public String getRequestParam(@RequestParam(defaultValue = "ssss") String param) {
//當請求url爲localhost:8080/test/requestParam時，param爲默認值ssss
    
//post-uri: localhost:8080/test/requestParam?param=xxx
@PostMapping(value = "test/requestParam")
public String getRequestParam(@RequestParam(name = "aa", required = false) String param) {
//指定參數爲「aa」，即當url爲localhost:8080/test/requestParam?aa=p1時，param爲p1
//當url爲localhost:8080/test/requestParam時，param爲null

//post-uri: localhost:8080/test/requestParam
@PostMapping(value = "test/requestParam")
public String postRequestParam(@RequestParam(required = false) int param) {
// int是基本類型，即便設置required=false，由於int沒法設置爲null仍然會報錯，能夠將int替換爲Integer
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• RestTemplate訪問：

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，默認值爲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());//輸出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，輸出結果爲null
}
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@RequestBody

• RequestBody主要經過請求體body傳值，經常使用來處理content-type=application/json請求，同時支持get和post請求，能獲取到body中的數據並轉化爲對象
• 支持get和post請求
• Controller聲明：

//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訪問：

//get請求
//RestTemplate的get請求不支持設置body，因此使用restTemplate沒法調用get請求的@RequestBody註解，但使用PostMan等工具是能夠發送帶body的get請求的

//post請求
public static void postRequestBody() {
    HttpHeaders requestHeaders = new HttpHeaders();
    //注意設置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());//輸出name4
}

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@ModelAttribute

• ModelAttribute註解參數時，發送請求的content-type須要爲"x-www-form-urlencoded"
• 僅支持post請求且content-type=x-www-form-urlencoded能接收到數據；若是是post請求且content-type=application/json、get請求且content-type=x-www-form-urlencoded、get請求且content-type=application/json均不會報錯但沒法接收到數據
• Controller聲明：

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

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", "用戶名");
    params.add("paramName", "123456");
    HttpEntity<MultiValueMap<String, String>> requestEntity = new HttpEntity<>(params, requestHeaders);
    RestTemplate restTemplate = new RestTemplate();
    //須要提供自定義convert
    restTemplate.getMessageConverters().add(new TestMappingJackson2HttpMessageConverter());
    ResponseEntity<String> responseEntity = restTemplate.postForEntity(host+"/test/modelAttribute",
            requestEntity, String.class);
    System.out.println("postModelAttribute: " + responseEntity.getBody());//輸出123456
}
    
//自定義convert
public class TestMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {
    public TestMappingJackson2HttpMessageConverter() {
        List<MediaType> mediaTypes = new ArrayList<>();
        mediaTypes.add(MediaType.TEXT_PLAIN);
        //添加form-urlencoded類型轉換
        mediaTypes.add(MediaType.APPLICATION_FORM_URLENCODED);
        setSupportedMediaTypes(mediaTypes);
    }
}
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以上對@PathVariable、@RequestParam、@RequestBody、@ModelAttribute的使用方式及RestTemplate如何調用相應註解接口作了總結，若有不對歡迎指出，謝謝！

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