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：

资源由URI来指定
显示使用HTTP方式(GET/POST/PUT/DELETE，查/增/改/删)
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：

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);
  }
}

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();
  }
}

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。