Java】JSON踩坑02 -- RestTemplate使用总结

日常工作中肯定会遇到服务之间的调用，尤其是现在都是微服务的架构，所以总结一下restTemplate的最常用的用法以及自己踩过的坑。

restTemplate的使用

restTemplate底层调用的是Execute方法，而Execute底层调用的是doExecute，它是基于http协议的，底层还是httpClient 的使用。

/**
     * Execute the given method on the provided URI.
     * <p>The {@link ClientHttpRequest} is processed using the {@link RequestCallback};
     * the response with the {@link ResponseExtractor}.
     * @param url the fully-expanded URL to connect to
     * @param method the HTTP method to execute (GET, POST, etc.)
     * @param requestCallback object that prepares the request (can be {@code null})
     * @param responseExtractor object that extracts the return value from the response (can be {@code null})
     * @return an arbitrary object, as returned by the {@link ResponseExtractor}
     */
    @Nullable
    protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback,
            @Nullable ResponseExtractor<T> responseExtractor) throws RestClientException {
 
        Assert.notNull(url, "URI is required");
        Assert.notNull(method, "HttpMethod is required");
        ClientHttpResponse response = null;
        try {
            ClientHttpRequest request = createRequest(url, method);
            if (requestCallback != null) {
                requestCallback.doWithRequest(request);
            }
            response = request.execute();
            handleResponse(url, method, response);
            return (responseExtractor != null ? responseExtractor.extractData(response) : null);
        }
        catch (IOException ex) {
            String resource = url.toString();
            String query = url.getRawQuery();
            resource = (query != null ? resource.substring(0, resource.indexOf('?')) : resource);
            throw new ResourceAccessException("I/O error on " + method.name() +
                    " request for \"" + resource + "\": " + ex.getMessage(), ex);
        }
        finally {
            if (response != null) {
                response.close();
            }
        }
    }

我们一般都是用的restTepmlate的exchange方法，这个方法比较灵活，可以接受可变参数，重载方法也有很多。当然 restTemplate还有其他很多方法，而且遵循restFul风格，像PUT POST GET PATCH DELETE 等都有对应的方法，按需使用。这里就不贴源码了。

然后就贴一个使用案例代码上来：

public YourResponse sampleRestTepmlate (YourRequest request) throws Exception {
    UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(this.serviceUrl);
    builder.path("urlpath");
    log.info("url : {}, request : {}", builder.toUriString(), JsonUtils.toJson(request));
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);
    headers.set("headername","headervalue");
    headers.add("anotherway", "value");
    HttpEntity<YourRequest> requestEntity = new HttpEntity<>(request, headers);
    ResponseEntity<YourResponse> responseEntity = null;
    try {
        responseEntity = restTemplate.exchange(builder.toUriString(), HttpMethod.POST, requestEntity,
                    YourResponse.class);
        return responseEntity.getBody();
    } catch (Exception e) {
        log.error("exception:{}",e.getMessage());
    }
}

踩坑大道

这里就要说一下我遇到的坑了。在使用restTemplate的时候，当你的call没有成功返回200的时候，比如返回400 500之类的，restTemplate里面有一个DefaultResponseErrorHandler，他会自动拦截住这些httpstatus 为400 500的response然后给你抛出一个异常。这就意味着，当你也想拿到带有错误信息的response的时候，他不会给你！它会给你抛出exception并且只是给你返回一个简单的类似500 Internal error! WTF！

贴上这段坑爹的代码：

/**
     * Handle the error in the given response with the given resolved status code.
     * <p>This default implementation throws a {@link HttpClientErrorException} if the response status code
     * is {@link org.springframework.http.HttpStatus.Series#CLIENT_ERROR}, a {@link HttpServerErrorException}
     * if it is {@link org.springframework.http.HttpStatus.Series#SERVER_ERROR},
     * and a {@link RestClientException} in other cases.
     * @since 5.0
     */
    protected void handleError(ClientHttpResponse response, HttpStatus statusCode) throws IOException {
        switch (statusCode.series()) {
            case CLIENT_ERROR:
                throw new HttpClientErrorException(statusCode, response.getStatusText(),
                        response.getHeaders(), getResponseBody(response), getCharset(response));
            case SERVER_ERROR:
                throw new HttpServerErrorException(statusCode, response.getStatusText(),
                        response.getHeaders(), getResponseBody(response), getCharset(response));
            default:
                throw new UnknownHttpStatusCodeException(statusCode.value(), response.getStatusText(),
                        response.getHeaders(), getResponseBody(response), getCharset(response));
        }
    }

脱坑之计

遇到了坑就不要害怕，这个问题可以这么解决：

1.不用restTemplate去请求，可以采用httpClient底层去实现

2.重写handleError方法，自定义ErrorHandle继承DefaultResponseErrorHandler

在已经写完实现之后，我选择方式2 : )

@Builder
@Slf4j
public class MyErrorHandle extends DefaultResponseErrorHandler {
 
    @Override
    public void handleError(ClientHttpResponse response, HttpStatus statusCode) throws IOException {
        int status = statusCode.value();
        if (status == 200 || status == 400 || status == 500) {
            //do what u want to do
        } else {
            super.handleError(response,statusCode);
        }
    }
}

然后在初始化restTemplate的时候调用setErrorHandle方法就可以了。

1	`restTemplate.setErrorHandler(YourErrorHandle).`

至于方式一这里不提了。

导入证书

有的时候当我们调用对方的server时，基于https 的协议是需要导入证书的，那我们该怎么把证书融入到restTemplate中呢？（又一个坑）

@Bean
    public RestTemplate buildRestTemplateWithinSSl(@Value("${service.connectTimeout}") int connectTimeout,
      @Value("${service.readTimeout}") int readTimeout,
      @Value("${service.sslFilePath}") String filePath,
      @Value("${service.sslpassword}") String sslPassword) throws Exception{
       
    RestTemplate template = restTemplateBuilder.setConnectTimeout(connectTimeout).setReadTimeout(readTimeout).build();
    String workingDirectory = BeanUtility.getWorkingDirectory();
    SSLContext sslContext = new SSLContextBuilder().loadTrustMaterial(new File(workingDirectory + "/" + filePath), sslPassword.toCharArray()).build();
    SSLConnectionSocketFactory socketFactory = new SSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE);
    CloseableHttpClient httpClient = HttpClients.custom().setSSLSocketFactory(socketFactory).build();
    HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory(httpClient);
    template.setRequestFactory(factory);
    return template;
    }

相当于重新给RequestFactory值，构造一个已经带有ssl证书的factory给他。

这里注意两个地方：

1	`SSLConnectionSocketFactory socketFactory =` `new` `SSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE);`

这里有个参数是NoopHostnameVerifier.INSTANCE，这里是可以无视ip的，也就是ip或者域名形式都可以。 (适用于对方给我提供证书和 ip地址，试了半天死活不通的情况。。)

第二个就是一个工具类的使用，我相信很多时候new file的时候很容易被路径绕晕。

1	`String workingDirectory = BeanUtility.getWorkingDirectory();`

这个工具类获得的路径不用你去担心，只要你的jks文件和你的jar包同级就行。管他什么环境什么路径，很方便。

贴上地址： github.com/AnsonCong/A…

本地调试证书导入jdk就行。

记录下导入证书的方法：

1	`keytool -import` `-alias {别名} -file {路径\证书名}.cer -keystore` `"{jdk路径\jre\lib\security\cacerts}"` `-storepass {password} -trustcacerts`

删除证书：