J2EE 练习题

J2EE 练习题 - JSON HTTP Service

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1 要求

2 示例代码

        2.1 Server 端

        2.2 客户端 - Java

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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

   <project 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">
       <modelVersion>4.0.0</modelVersion>
       <groupId>lld</groupId>
       <artifactId>http.json.test.server</artifactId>
       <packaging>war</packaging>
       <version>0.0.1-SNAPSHOT</version>
       <name>http.json.test.server Maven Webapp</name>
       <url>http://maven.apache.org</url>
       <properties>
           <gson.version>2.8.2</gson.version>
           <tomcat.version>6.0.53</tomcat.version>
       </properties>
       <dependencies>
           <dependency>
               <groupId>com.google.code.gson</groupId>
               <artifactId>gson</artifactId>
               <version>${gson.version}</version>
           </dependency>
           <dependency>
               <groupId>org.apache.tomcat</groupId>
               <artifactId>servlet-api</artifactId>
               <version>${tomcat.version}</version>
               <scope>provided</scope>
           </dependency>
           <dependency>
               <groupId>junit</groupId>
               <artifactId>junit</artifactId>
               <version>3.8.1</version>
               <scope>test</scope>
           </dependency>
       </dependencies>
       <build>
           <finalName>http.json.test.server</finalName>
       </build>
   </project>

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

   <!DOCTYPE web-app PUBLIC
    "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd" >
   
   <web-app>
       <display-name>HTTP JSON Service Demo</display-name>
       <servlet>
           <servlet-name>getUser</servlet-name>
           <servlet-class>http.json.test.server.servlet.UserServlet</servlet-class>
       </servlet>
   
       <servlet-mapping>
           <servlet-name>getUser</servlet-name>
           <url-pattern>/getUser.do</url-pattern>
       </servlet-mapping>
   </web-app>
   

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

   <project 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">
       <modelVersion>4.0.0</modelVersion>
   
       <groupId>lld</groupId>
       <artifactId>http.json.test.client</artifactId>
       <version>0.0.1-SNAPSHOT</version>
       <packaging>jar</packaging>
   
       <name>http.json.test.client</name>
       <url>http://maven.apache.org</url>
   
       <properties>
           <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
       </properties>
   
       <dependencies>
           <dependency>
               <groupId>org.apache.httpcomponents</groupId>
               <artifactId>httpclient</artifactId>
               <version>4.5.2</version>
           </dependency>
       </dependencies>
   </project>

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<String, String> parameters) throws ClientProtocolException, IOException {
           return callHttpService(url, parameters, "utf-8");
       }
       
       public static String callHttpService(String url, Map<String, String> parameters, String charset) throws ClientProtocolException, IOException {
           String result = null;
           HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
           CloseableHttpClient httpClient = httpClientBuilder.build();
           HttpPost httpPost = new HttpPost(url);
   
           List<NameValuePair> list = new ArrayList<NameValuePair>();
   
           if (parameters != null) {
               Iterator<Map.Entry<String, String>> iterator = parameters.entrySet().iterator();
   
               while (iterator.hasNext()) {
                   Entry<String, String> entry = (Entry<String, 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<string, string=""> parameters = new HashMap<string, string="">();
           parameters.put("userId", "lld");
           String result = HttpRequestUtil.callHttpService(url, parameters);
           System.out.println("Result is: ");
           System.out.println(result);        
       }
   }