Spring 50例常见错误（十八）

文章整理来源：Spring编程常见错误50例_spring_spring编程_bean_AOP_SpringCloud_SpringWeb_测试_事务_Data-极客时间

        定义一个接口，然后使用 RestTemplate 向这个接口发送请求，并在请求中定义一个 Map 做请求参数表单。

@RestController
public class HelloWorldController {
    @RequestMapping(path = "hi", method = RequestMethod.POST)
    public String hi(@RequestParam("para1") String para1, @RequestParam("para2") String para2){
        return "helloworld:" + para1 + "," + para2;
    };
}

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RestTemplate template = new RestTemplate();
Map paramMap = new HashMap();
paramMap.put("para1", "001");
paramMap.put("para2", "002");

String url = "http://localhost:8080/hi";
String result = template.postForObject(url, paramMap, String.class);
System.out.println(result);

        测试返回提示 400 错误，即请求中缺少 para1 表单参数

        解析：发送请求的时候，会根据当前提交的 Body 内容，遍历当前支持的所有编码解码器，找到适合的进行 Body 内容的序列化。

public void doWithRequest(ClientHttpRequest httpRequest) throws IOException {
   super.doWithRequest(httpRequest);
   Object requestBody = this.requestEntity.getBody();
   if (requestBody == null) {
       //省略其他非关键代码
   }
   else {
      Class requestBodyClass = requestBody.getClass();
      Type requestBodyType = (this.requestEntity instanceof RequestEntity ?
            ((RequestEntity)this.requestEntity).getType() : requestBodyClass);
      HttpHeaders httpHeaders = httpRequest.getHeaders();
      HttpHeaders requestHeaders = this.requestEntity.getHeaders();
      MediaType requestContentType = requestHeaders.getContentType();
      for (HttpMessageConverter messageConverter : getMessageConverters()) {
         if (messageConverter instanceof GenericHttpMessageConverter) {
            GenericHttpMessageConverter