RestTemplate获取HTTP状态码

背景

• 使用RestTemplate请求特定接口，并根据获取的HTTP状态码进行具体业务操作。

@RestController
public class RestfulController {
    private RestTemplate restTemplate = new RestTemplate();

    @GetMapping("/test1")
    public void test1(HttpServletResponse response) {
        response.setStatus(403);
    }

    @GetMapping("/test2")
    public void test2() {
        ResponseEntity responseEntity = restTemplate.exchange("http://127.0.0.1:8080/test1", HttpMethod.GET, new HttpEntity(null, new HttpHeaders()), String.class);
        int code = responseEntity.getStatusCodeValue();
        // 具体业务操作...
    }
}

报错

org.springframework.web.client.HttpClientErrorException$Forbidden: 403 null

解决

• 如果想要使用responseEntity.getStatusCodeValue()等，需要先为RestTemplate对象设置ResponseErrorHandler。
• 需要注意代码并不符合平常的开发规范，只是为了实现效果。

@RestController
public class RestfulController {
    private RestTemplate restTemplate = new RestTemplate();

    @GetMapping("/test1")
    public void test1(HttpServletResponse response) {
        response.setStatus(403);
    }

    @GetMapping("/test2")
    public void test2() {
        restTemplate.setErrorHandler(new RestfulController.ErrorHandler());
        ResponseEntity responseEntity = restTemplate.exchange("http://127.0.0.1:8080/test1", HttpMethod.GET, new HttpEntity(null, new HttpHeaders()), String.class);
        int code = responseEntity.getStatusCodeValue();
        // 业务处理...
    }

    static class ErrorHandler implements ResponseErrorHandler {

        @Override
        public boolean hasError(ClientHttpResponse clientHttpResponse) throws IOException {
            if (200 == clientHttpResponse.getRawStatusCode()) {
                return false;
            }
            return true;
        }

        @Override
        public void handleError(ClientHttpResponse clientHttpResponse) throws IOException {
            // 处理Error...
        }
    }
}

原因

• RestTemplate

public class RestTemplate extends InterceptingHttpAccessor implements RestOperations {
	...
    private ResponseErrorHandler errorHandler;
    ...

    public RestTemplate() {
        ...
        // 默认的ResponseErrorHandler
        this.errorHandler = new DefaultResponseErrorHandler();
        ...
    }

	...

	@Nullable
    protected  T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback, @Nullable ResponseExtractor responseExtractor) throws RestClientException {
        Assert.notNull(url, "URI is required");
        Assert.notNull(method, "HttpMethod is required");
        ClientHttpResponse response = null;

        Object var14;
        try {
            ClientHttpRequest request = this.createRequest(url, method);
            if (requestCallback != null) {
                requestCallback.doWithRequest(request);
            }

            response = request.execute();
            
            // 处理Response, 这里如果抛出异常，就不会返回ResponseEntity对象
            this.handleResponse(url, method, response);
            
            var14 = responseExtractor != null ? responseExtractor.extractData(response) : null;
        } catch (IOException var12) {
            String resource = url.toString();
            String query = url.getRawQuery();
            resource = query != null ? resource.substring(0, resource.indexOf(63)) : resource;
            throw new ResourceAccessException("I/O error on " + method.name() + " request for \"" + resource + "\": " + var12.getMessage(), var12);
        } finally {
            if (response != null) {
                response.close();
            }

        }

        return var14;
    }

	protected void handleResponse(URI url, HttpMethod method, ClientHttpResponse response) throws IOException {
        ResponseErrorHandler errorHandler = this.getErrorHandler();
        boolean hasError = errorHandler.hasError(response);
        if (this.logger.isDebugEnabled()) {
            try {
                int code = response.getRawStatusCode();
                HttpStatus status = HttpStatus.resolve(code);
                this.logger.debug("Response " + (status != null ? status : code));
            } catch (IOException var8) {
            }
        }

        if (hasError) {
        	// 处理Http错误码
            errorHandler.handleError(url, method, response);
        }

    }

	...
}

• DefaultResponseErrorHandler

public class DefaultResponseErrorHandler implements ResponseErrorHandler {
    public DefaultResponseErrorHandler() {
    }

    public boolean hasError(ClientHttpResponse response) throws IOException {
        int rawStatusCode = response.getRawStatusCode();
        HttpStatus statusCode = HttpStatus.resolve(rawStatusCode);
        return statusCode != null ? this.hasError(statusCode) : this.hasError(rawStatusCode);
    }

    protected boolean hasError(HttpStatus statusCode) {
        return statusCode.isError();
    }

    protected boolean hasError(int unknownStatusCode) {
        Series series = Series.resolve(unknownStatusCode);
        return series == Series.CLIENT_ERROR || series == Series.SERVER_ERROR;
    }

    public void handleError(ClientHttpResponse response) throws IOException {
        HttpStatus statusCode = HttpStatus.resolve(response.getRawStatusCode());
        if (statusCode == null) {
            throw new UnknownHttpStatusCodeException(response.getRawStatusCode(), response.getStatusText(), response.getHeaders(), this.getResponseBody(response), this.getCharset(response));
        } else {
            this.handleError(response, statusCode);
        }
    }

    protected void handleError(ClientHttpResponse response, HttpStatus statusCode) throws IOException {
        String statusText = response.getStatusText();
        HttpHeaders headers = response.getHeaders();
        byte[] body = this.getResponseBody(response);
        Charset charset = this.getCharset(response);
        switch(statusCode.series()) {
        case CLIENT_ERROR:
            throw HttpClientErrorException.create(statusCode, statusText, headers, body, charset);
        case SERVER_ERROR:
            throw HttpServerErrorException.create(statusCode, statusText, headers, body, charset);
        default:
            throw new UnknownHttpStatusCodeException(statusCode.value(), statusText, headers, body, charset);
        }
    }
    
    ...
}

• RestTemplate中的getForEntity(…)、 getForObject(…)、exchange(…)和delete(…)等方法最终都是调用doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback, @Nullable ResponseExtractor responseExtractor)方法。
• 从源代码可以看出来默认的处理器DefaultResponseErrorHandler，最后会抛出三种异常：HttpClientErrorException、HttpServerErrorException、UnknownHttpStatusCodeException。所以在得到ResponseEntity返回值之前，就有异常抛出。
• 可以自定义错误处理器，自定义的处理器并没有抛出异常，所以也就可以返回ResponseEntity对象，并通过该对象的getStatusCodeValue()方法获取HTTP状态码。