J2EE 练习题 - JSON HTTP Service

1 要求

2 示例代码

        2.1 Server 端

        2.2 客户端 - Java

1 要求

在 Tomcat 上布署一个 HTTP Service，使用 JSON 格式返回数据

2 示例代码

2.1 Server 端

基于 Maven 开发

1. 新建 Maven webapp 项目

2. 修改 pom.xml 如下

   pom.xml

   xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
       4.0.0
       lld
       http.json.test.server
       war
       0.0.1-SNAPSHOT
       http.json.test.server Maven Webapp
       http://maven.apache.org
       
           2.8.2
           6.0.53
       
       
           
               com.google.code.gson
               gson
               ${gson.version}
           
           
               org.apache.tomcat
               servlet-api
               ${tomcat.version}
               provided
           
           
               junit
               junit
               3.8.1
               test
           
       
       
           http.json.test.server
       
   

3. 创建 POJO 类 User.java

   User.java

   package http.json.test.server.model;
   
   public class User {
       private String userId;
       private String userName;
   
       public String getUserId() {
           return userId;
       }
   
       public void setUserId(String userId) {
           this.userId = userId;
       }
   
       public String getUserName() {
           return userName;
       }
   
       public void setUserName(String userName) {
           this.userName = userName;
       }
   }
   

4. 创建 Servlet 类 UserServlet

   UserServlet.java

   package http.json.test.server.servlet;
   
   import java.io.IOException;
   
   import javax.servlet.ServletException;
   import javax.servlet.ServletOutputStream;
   import javax.servlet.http.HttpServlet;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   
   import com.google.gson.Gson;
   
   import http.json.test.server.model.User;
   
   public class UserServlet extends HttpServlet {
   
       private static final long serialVersionUID = -2118394734647389638L;
   
       @Override
       protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           this.doPost(req, resp);
       }
       
       @Override
       protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           User user = new User();
           String userId = req.getParameter("userId");
           user.setUserId(userId);
           user.setUserName("Lindong");
           String jsonString = new Gson().toJson(user);
           ServletOutputStream outputStream = resp.getOutputStream();
           outputStream.print(jsonString);
       }
   }
   

5. 修改 web.xml 如下所示

   web.xml

   web-app PUBLIC
    "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd" >
   
   
       HTTP JSON Service Demo
       
           getUser
           http.json.test.server.servlet.UserServlet
       
   
       
           getUser
           /getUser.do
       
   
   

6. 编译并打包

   mvn clean package

7. 将生成的 war 包复制到 Tomcat webapps 目录并启动 Tomcat，打开浏览器输入 http://localhost:8080/http.json.test.server/getUser.do?userId=10001 后在浏览器中显示结果：

   {"userId":"10001","userName":"Lindong"}

2.2 客户端 - Java

使用 Java 程序获取 Service 响应

1. 使用 Maven 创建 quickstart 程序

2. 修改 pom.xml 如下

   pom.xml

   xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
       4.0.0
   
       lld
       http.json.test.client
       0.0.1-SNAPSHOT
       jar
   
       http.json.test.client
       http://maven.apache.org
   
       
           UTF-8
       
   
       
           
               org.apache.httpcomponents
               httpclient
               4.5.2
           
       
   

3. 创建工具类 HttpRequestUtil.java

   HttpRequestUtil.java

   package lld.http.json.test.client.util;
   
   import java.io.IOException;
   import java.util.ArrayList;
   import java.util.Iterator;
   import java.util.List;
   import java.util.Map;
   import java.util.Map.Entry;
   
   import org.apache.http.HttpEntity;
   import org.apache.http.HttpResponse;
   import org.apache.http.NameValuePair;
   import org.apache.http.client.ClientProtocolException;
   import org.apache.http.client.entity.UrlEncodedFormEntity;
   import org.apache.http.client.methods.HttpPost;
   import org.apache.http.impl.client.CloseableHttpClient;
   import org.apache.http.impl.client.HttpClientBuilder;
   import org.apache.http.message.BasicNameValuePair;
   import org.apache.http.util.EntityUtils;
   
   public class HttpRequestUtil {
       public static String callHttpService(String url, Map parameters) throws ClientProtocolException, IOException {
           return callHttpService(url, parameters, "utf-8");
       }
       
       public static String callHttpService(String url, Map parameters, String charset) throws ClientProtocolException, IOException {
           String result = null;
           HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
           CloseableHttpClient httpClient = httpClientBuilder.build();
           HttpPost httpPost = new HttpPost(url);
   
           List list = new ArrayList>();
   
           if (parameters != null) {
               Iterator> iterator = parameters.entrySet().iterator();
   
               while (iterator.hasNext()) {
                   Entry entry = (Entry, String>) iterator.next();
                   list.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
               }
           }
   
           if (list.size() > 0) {
               UrlEncodedFormEntity entity = new UrlEncodedFormEntity(list, charset);
               httpPost.setEntity(entity);
           }
           
           HttpResponse response = httpClient.execute(httpPost);
   
           if (response != null) {
               HttpEntity responseEntity = response.getEntity();
               
               if (responseEntity != null) {
                   result = EntityUtils.toString(responseEntity);
               }
           }
           
           return result;
       }
   }

4. 调用 Http Service 例程

   App.java

   package lld.http.json.test.client;
   
   import java.io.IOException;
   import java.util.HashMap;
   import java.util.Map;
   
   import org.apache.http.client.ClientProtocolException;
   
   import lld.http.json.test.client.util.HttpRequestUtil;
   
   /**
    * Hello world!
    *
    */
   public class App 
   {
       public static void main( String[] args ) throws ClientProtocolException, IOException
       {
           String url = "http://localhost:8080/http.json.test.server/getUser.do";
           Map parameters = new HashMap();
           parameters.put("userId", "lld");
           String result = HttpRequestUtil.callHttpService(url, parameters);
           System.out.println("Result is: ");
           System.out.println(result);        
       }
   }