2019独角兽企业重金招聘Python工程师标准>>> 
1、思考
面向服务编程中，我们经常需要通过HttpClient请求服务器获取对应的数据服务，如果你使用RestTemplate，肯定会在会他的 上传、下载，因为一般的Json数据请求都比较简单。下面就分享一下如何使用 RestTemplate 进行文件下载。
2、组件封装
package com.hnust.common.controller;
import com.hnust.common.rest.client.RestClient;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.http.*;
import org.springframework.http.client.ClientHttpRequestExecution;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.http.client.support.HttpRequestWrapper;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.RestController;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* Created by Heweipo on 2016/5/26.
*
* 资源下载通用控制器
*/
@RestController
public class DownloadController extends BaseController {
/**
* 发送/获取 服务端数据
* 注意 URL 、HttpMethod 都与当前请求保持一致
*
* @return 返回结果(响应体)
*/
protected ResponseEntity export() {
return export(null, null);
}
/**
* 主要是 GET、DELETE 请求不能发在body体
*
* @param uri 相对路径
* @return 返回结果(响应体)
*/
protected ResponseEntity export(String uri) {
return export(uri, null);
}
/**
* 添加参数
*
* @param params 请求body体
* @return 返回结果(响应体)
*/
protected ResponseEntity export(Map params) {
return export(null, params);
}
/**
* 下载通用方法
*
* @param params 请求参数
* @return 下载流
*/
protected ResponseEntity export(String uri, Map params) {
// RestClient.getServiceServerUrl() 服务器的URL ： http://localhost:8080/service
String url = RestClient.getServiceServerUrl() + request.getRequestURI();
if (!StringUtils.isEmpty(uri)) {
url = RestClient.getServiceServerUrl() + uri;
}
HttpMethod httpMethod = getMethod();
if(params == null) params = new HashMap<>();
url = processParams(url,httpMethod,params);
return export(url, httpMethod, params);
}
/**
* 下载通用方法
* @param url 地址
* @param method 方法
* @param params 参数
* @return 下载流
*/
protected ResponseEntity export(String url, HttpMethod method, Map params) {
ClientHttpRequestInterceptor interceptor = new DownloadInterceptor();
List list = new ArrayList<>();
list.add(interceptor);
restTemplate.setInterceptors(list);
// 请求头
HttpHeaders headers = new HttpHeaders();
ObjectMapper mapper = new ObjectMapper();
String str = null;
try {
if (params != null) {
str = mapper.writeValueAsString(params);
}
} catch (JsonProcessingException e) { // 这个异常不处理
e.printStackTrace();
}
// 发送请求
HttpEntity entity = new HttpEntity<>(str, headers);
ResponseEntity obj = restTemplate.exchange(url, method, entity, byte[].class);
return obj;
}
/**
* Spring RestTemplate 下载组件
*/
public static class DownloadInterceptor implements ClientHttpRequestInterceptor{
/**
* 媒体类型,给个默认值
*/
private MediaType headerValue = MediaType.ALL;
/**
* 获取媒体类型
* @return 媒体类型
*/
public MediaType getHeaderValue() {
return headerValue;
}
/**
* 设置媒体类型
* @param headerValue 媒体类型
*/
public void setHeaderValue(MediaType headerValue) {
this.headerValue = headerValue;
}
/**
* Intercept the given request, and return a response. The given {@link ClientHttpRequestExecution} allows
* the interceptor to pass on the request and response to the next entity in the chain.
*
*
A typical implementation of this method would follow the following pattern:
*
* - Examine the {@linkplain HttpRequest request} and body
* - Optionally {@linkplain HttpRequestWrapper wrap} the request to filter HTTP attributes.
* - Optionally modify the body of the request.
* - Either
*
* - execute the request using {@link ClientHttpRequestExecution#execute(HttpRequest, byte[])},
* or
* - do not execute the request to block the execution altogether.
*
* - Optionally wrap the response to filter HTTP attributes.
*
*
* @param request the request, containing method, URI, and headers
* @param body the body of the request
* @param execution the request execution
* @return the response
* @throws IOException in case of I/O errors
*/
@Override
public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
HttpRequestWrapper requestWrapper = new HttpRequestWrapper(request);
List list = new ArrayList<>();
list.add(headerValue);
requestWrapper.getHeaders().setAccept(list);
return execution.execute(requestWrapper, body);
}
}
}
3、组件调用
package com.hnust.workbench.common.questionbank.paper.controller;
import com.hnust.common.controller.DownloadController;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import java.util.Map;
/**
*
* Created by Heweipo on 2016/2/26.
*/
@RestController
public class ClientController extends DownloadController {
/**
* 下载
*
*/
@RequestMapping(value = "/download", method = RequestMethod.GET)
public ResponseEntity getBatchAnswer(){
return export();
}
}
4、注意
1）RestTemplate 在这里只是做了一下转发，因为真正的文件是从另一个服务URL那里获取
2）RestTemplate 还有就是上传以及文本数据获取，项目中使用一般都会进行封装，方便调用