RestTemplate分析

RestTemplate

示例

服务端

@RequestMapping("test")
    public String test(@RequestParam("uid") int uid) {
        logger.info("uid = {}", uid);
        return "test";
    }

客户端

代码一

public void send() {
        Map params = new HashMap();
        params.put("uid", 123);
        restTemplate.postForObject("http://localhost:8080/test", params, String.class, new HashMap());
    }

代码二

public void send() {
        MultiValueMap params = new LinkedMultiValueMap();
        params.add("uid", 123);
        restTemplate.postForObject("http://localhost:8080/test", params, String.class, new HashMap());
    }

经过测试发现代码二的请求能被服务端正常处理，而代码一则提示uid参数未能提供。

分析

客户端

public  T postForObject(String url, Object request, Class responseType, Map uriVariables)
            throws RestClientException {

        RequestCallback requestCallback = httpEntityCallback(request, responseType);
        HttpMessageConverterExtractor responseExtractor =
                new HttpMessageConverterExtractor(responseType, getMessageConverters(), logger);
        return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
    }

可以看到request和responseType被封装成了一个HttpEntityRequestCallback对象，继续跟HttpEntityRequestCallback源码

private HttpEntityRequestCallback(Object requestBody, Type responseType) {
            super(responseType);
            if (requestBody instanceof HttpEntity) {
                this.requestEntity = (HttpEntity) requestBody;
            }
            else if (requestBody != null) {
                this.requestEntity = new HttpEntity