HTTP/REST JAVA实现

一、REST

REST(Representational State Transfer)表现层状态转化，它是一种web架构风格、设计风格，提供一些约束条件和原则。REST原则如下：

1. 资源由URI来指定
2. 显示使用HTTP方式(GET/POST/PUT/DELETE，查/增/改/删)
3. 无状态

基于这个风格设计的软件可以更简介，更有层次，更易于实现缓存等机制。

二、JAVA访问

访问HTTP/REST服务目前主要就是使用不同的方法访问http服务。
这里主要提供三种访问示例：

1. 使用jdk自带的HttpURLConnection访问

   package com.yihengliu.http;
   
   import java.io.BufferedReader;
   import java.io.InputStreamReader;
   import java.net.HttpURLConnection;
   import java.net.URL;
   
   /**
   * HttpURLConnection测试
   *
   * @author liucheng
   * @version 0.1
   * @since 0.1 2018-01-08 上午9:18
   **/
   public class HttpURLConnectionTest {
     public static void main(String[] args) throws Exception {
         URL url = new URL("http://IP:8080/info/runningStatus");
         HttpURLConnection conn = (HttpURLConnection) url.openConnection();
   
         // 设置提交模式，访问认证
         conn.setRequestMethod("GET");
         conn.setRequestProperty("Authorization", "YY");
   
         // 设置提交格式
         conn.setRequestProperty("Content-Type", "application/json");
         conn.setConnectTimeout(15000);
         conn.setReadTimeout(15000);
   
         // 第一种获取返回值的方式
   //        byte[] bytes = new byte[1024];
   //        InputStream inStream = conn.getInputStream();
   //        inStream.read(bytes, 0, inStream.available());
   //        System.out.println(new String(bytes, "utf-8"));
   
         // 第二种获取返回值的方式
         BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
         StringBuffer stringBuffer = new StringBuffer();
         String line;
         while ((line = br.readLine()) != null) {
             stringBuffer.append(line);
             stringBuffer.append("
   ");
         }
         br.close();
         System.out.println(stringBuffer);
     }
   }
   

2. 使用apache提供的HttpClient访问

   package com.yihengliu.http;
   
   import org.apache.http.Header;
   import org.apache.http.HttpEntity;
   import org.apache.http.HttpResponse;
   import org.apache.http.NameValuePair;
   import org.apache.http.client.HttpClient;
   import org.apache.http.client.entity.UrlEncodedFormEntity;
   import org.apache.http.client.methods.HttpGet;
   import org.apache.http.client.methods.HttpPost;
   import org.apache.http.entity.StringEntity;
   import org.apache.http.impl.client.DefaultHttpClient;
   import org.apache.http.message.BasicNameValuePair;
   import org.apache.http.util.EntityUtils;
   
   import java.util.ArrayList;
   import java.util.List;
   
   /**
   * httpclient测试
   *
   * @author liucheng
   * @version 0.1
   * @since 0.1 2018-01-06 下午1:37
   **/
   public class HttpClientTest {
     /**
      * HttpClient 客户端访问
      */
     private static void httpClientVisit() {
         String clientResponse = "";
         String url = "http://IP:8080/info/runningStatus";
         try {
             HttpClient client = new DefaultHttpClient();
             HttpPost request = new HttpPost(url);
   
             StringEntity entity = new StringEntity("", "UTF-8");
             entity.setContentType("text/xml");
             request.setEntity(entity);
   
             HttpResponse response = client.execute(request);
             org.apache.http.HttpEntity httpEntity = response.getEntity();
             if (httpEntity != null) {
                 clientResponse = EntityUtils.toString(httpEntity, "UTF-8");
             }
   
             if (clientResponse == null || "".equals(clientResponse)) {
                 System.err.println("clientResponse is null or empty");
             }
   
             System.out.println(clientResponse);
   
         } catch (Exception e) {
             e.printStackTrace();
         }
     }
   
     /**
      * post 方式提交表单
      */
     public static void postForm() {
        String url ="http://IP:8080/userLoginController/userLogin";
   
         HttpClient client = new DefaultHttpClient();
         HttpPost httpPost = new HttpPost(url);
   
         List<NameValuePair> formParams = new ArrayList<NameValuePair>();
         formParams.add(new BasicNameValuePair("userAccount", "admin"));
         formParams.add(new BasicNameValuePair("userPassword", "123456"));
         UrlEncodedFormEntity uefEntity;
         try {
             uefEntity = new UrlEncodedFormEntity(formParams, "UTF-8");
             httpPost.setEntity(uefEntity);
             System.out.printf("executing request " + httpPost.getURI());
             HttpResponse response = client.execute(httpPost);
             Header[] headers = response.getAllHeaders();
             for (int i = 0; i < headers.length; i++) {
                 System.out.println(headers[i].getName());
             }
   
             try {
                 HttpEntity entity = response.getEntity();
                 if (entity != null) {
                     System.out.printf("Response content: " + EntityUtils.toString(entity, "UTF-8"));
                 }
             } catch (Exception e) {
                 e.printStackTrace();
             }
         } catch (Exception e) {
             e.printStackTrace();
         }
     }
   
     /**
      * get 请求
      */
     public static void getRequest() {
         try {
             HttpClient client = new DefaultHttpClient();
   
             HttpGet httpGet = new HttpGet("http://www.baidu.com");
             System.out.println("executing request " + httpGet.getURI());
             HttpResponse response = client.execute(httpGet);
   
             try {
                 HttpEntity entity = response.getEntity();
                 System.out.println(response.getStatusLine());
                 if (entity != null) {
                     System.out.println("Response content length: " + entity.getContentLength());
                     System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));
                 }
             } catch (Exception e) {
   
             }
         } catch (Exception e) {
   
         }
     }
   
     public static void main(String[] args) {
   //        httpClientVisit();
   //        postForm();
           getRequest();
     }
   }
   

3. 使用sprint-web提供的RestTemplate访问

   package com.yihengliu.http;
   
   import org.springframework.http.HttpEntity;
   import org.springframework.http.HttpHeaders;
   import org.springframework.http.client.SimpleClientHttpRequestFactory;
   import org.springframework.web.client.RestTemplate;
   
   /**
   * RestTemplate 访问测试
   *
   * @author liucheng
   * @version 0.1
   * @since 0.1 2018-01-06 下午2:27
   **/
   public class RestTemplateTest {
     private static void restTemplateVisit() {
         String returnXml = "";
   
         try {
             SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
             requestFactory.setConnectTimeout(1000);
             requestFactory.setReadTimeout(1000);
   
             RestTemplate restTemplate = new RestTemplate(requestFactory);
   
             HttpHeaders requestHeaders = new HttpHeaders();
             requestHeaders.set("Accept-Charset", "utf-8");
             requestHeaders.set("Content-type", "text/xml; charset=utf-8");
   
             HttpEntity<String> entity = new HttpEntity<>("", requestHeaders);
             String url = "http://IP:8080/info/runningStatus";
             returnXml = restTemplate.postForObject(url, entity, String.class);
   
             System.out.println(returnXml);
   
         } catch (Exception e) {
            e.printStackTrace();
         }
     }
   
     public static void main(String[] args) {
        restTemplateVisit();
     }
   }
   

三、JAVA提供服务

主要需要根据REST的原则设计出符合要求的“RESTful API”。
可参考文章: Principles of good RESTful API Design

早期的MVC设计并不能提供RESTful的服务，而只是支持GET和POST服务请求。