Resttemplate请求失败如何获取返回的json

参考：https://blog.csdn.net/u011974797/article/details/82424004

https://www.cnblogs.com/liumz0323/p/10633785.html

问题描述：后台用Resttemplate请求失败的话只会在后台报错400，不会返回json错误原因
解决方法：使用HttpClientErrorException异常捕捉

try {
    // resttemplate call api
} catch (HttpClientErrorException e) {
    //捕捉HTTP异常
    e.getResponseBodyAsString();
} catch (Exception e) {
    //捕捉所有异常
    e.printStackTrace();
}

描述：使用RestTemplate请求url，由于Token等验证信息参数失效，报出 401 HttpClientErrorException异常。
并且获取不到body消息体的错误信息。然而postman工具，是可以返回错误信息的。

原因：RestTemplate 有自己的默认错误处理。在默认的处理里，判断接收到401状态码则抛出
HttpClientErrorException异常，并执行了response.getBody()，这就导致我们后续获取不到body消息体了。

　　全局异常处理

@ControllerAdvice
public class ExceptionHandlerController {
    
    @ExceptionHandler(HttpClientErrorException.class)
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    public void HttpClientErrorExceptionHandler(HttpClientErrorException ex, HttpServletResponse res) {
        UtilFunctions.log.error("HttpClientErrorExceptionHandler, msg: {}, exception: {}", ex.toString(), ex);
        UtilFunctions.reportError("HttpClientErrorExceptionHandler: " + ex.toString(), ex, null);
        JSONObject response = new JSONObject();
        response.put("message", ex.getResponseBodyAsString());
        res.setContentType("application/json;charset=utf-8");
        try {
            res.getWriter().append(response.toString());
        } catch (IOException e) {
            UtilFunctions.log.error("IOException, exception: {}", e.getMessage(), e);
        }
    }
}

/*
 * 因为Content-Type=application/x-www-form-urlencoded, 所以post请求body中的参数格式也是 a=xxx&b=xxx;
 * params可以为null
 * 
 */
private static HttpEntity<String> requestEntityRequireAuth(HttpServletRequest request, String params) {
    HttpHeaders requestHeaders = new HttpHeaders();
    requestHeaders.add("Authorization", getAuthorization(request));
    requestHeaders.add("accept", "*/*");
    requestHeaders.add("connection", "Keep-Alive");
    requestHeaders.add("Content-Type", "application/x-www-form-urlencoded");
    requestHeaders.add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0");
    HttpEntity<String> requestEntity = new HttpEntity<String>(params, requestHeaders);
    return requestEntity;
}

private static HttpEntity<String> requestEntityNotRequireAuth(HttpServletRequest request, String params) {
    HttpHeaders requestHeaders = new HttpHeaders();
    requestHeaders.add("accept", "*/*");
    requestHeaders.add("connection", "Keep-Alive");
    requestHeaders.add("Content-Type", "application/x-www-form-urlencoded");
    requestHeaders.add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0");
    HttpEntity<String> requestEntity = new HttpEntity<String>(params, requestHeaders);
    return requestEntity;
}

private static JSONObject returnResult(ResponseEntity<Object> result, HttpServletResponse response) {
    int status = result.getStatusCodeValue();
    JSONObject obj = new JSONObject();
    if (status == 200) {
        obj.put("data", result.getBody());
    } else {
        response.setStatus(status);
        obj.put("message", result.getBody());
    }
    
    return obj;
}

private static JSONObject exceptionReturnResult(HttpClientErrorException e, HttpServletResponse response) {
    int statusCode = e.getStatusCode().value();
    JSONObject obj = new JSONObject();
    response.setStatus(statusCode);
    obj.put("message", e.getResponseBodyAsString());
    return obj;
}

/**
 * GET请求，需要认证，返回结果中data为JSONObject
 */
public static Object getForObjectRequireAuth(HttpServletRequest request, HttpServletResponse response, String uri) throws Exception {
    // 通过ContextProvider从spring容器获取RestTemplate实例
    RestTemplate restTemplate = ContextProvider.getBean(RestTemplate.class);
    ResponseEntity<Object> result = null;
    try {
        result = restTemplate.exchange(Config.BASE_SITE + uri, HttpMethod.GET, requestEntityRequireAuth(request, null), Object.class);
    } catch (HttpClientErrorException  e) {
        return exceptionReturnResult(e, response);
    }
    return returnResult(result, response);
}