$Java HttpClient庫的使用

（一）簡介

HttpClient是Apache的一個開源庫，相比於JDK自帶的URLConnection等，使用起來更靈活方便。

使用方法可以大致分為如下八步曲：

1、創建一個HttpClient對象;

2、創建一個Http請求對象並設置請求的URL，比如GET請求就創建一個HttpGet對象，POST請求就創建一個HttpPost對象;

3、如果需要可以設置請求對象的請求頭參數，也可以往請求對象中添加請求參數;

4、調用HttpClient對象的execute方法執行請求;

5、獲取請求響應對象和響應Entity;

6、從響應對象中獲取響應狀態，從響應Entity中獲取響應內容;

7、關閉響應對象;

8、關閉HttpClient.

 

（二）在本地創建一個Servlet程序

在本地創建一個Servlet程序並跑在Tomcat服務器中，主要用於下一步測試HttpClient發送請求。

注：Servlet的創建方法詳見：微信公眾號開發【技術基礎】（一）：Eclipse+Tomcat搭建本地服務器並跑通HelloWorld程序

1、Servlet類：

import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloWorld extends HttpServlet {
    private static final long serialVersionUID = 4601029764222607869L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
        // 1. 設置編碼格式
        resp.setContentType("text/html");
        resp.setCharacterEncoding("UTF-8");

        // 2. 往返回體中寫返回數據
        PrintWriter writer = null;
        try {
            writer = resp.getWriter();
            writer.print("Hello world! 你好，世界！！");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            writer.close();
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        // 1. 獲取請求的參數
        String userName = req.getParameter("username");
        String password = req.getParameter("password");

        // 2. 往返回體寫返回數據
        PrintWriter writer = null;
        try {
            writer = resp.getWriter();
            writer.print("your username is:" + userName + "\nyour password is:" + password);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            writer.close();
        }
    }

}

 

2、web.xml（新加內容）：

　　<servlet>
        <servlet-name>helloWorld</servlet-name>
        <servlet-class>com.servlet.HelloWorld</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>helloWorld</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

 

（三）測試HttpClient發送GET和POST請求

1、HttpClient測試類：

package com.test.method;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.ParseException;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

/**
 * 測試HttpClient發送各種請求的方法
 * 
 * @author Administrator
 *
 */
public class HttpClientTest {
    // 發送請求的url
    public static final String REQUEST_URL = "http://localhost:8080/TomcatTest/hello";

    /**
     * 測試發送GET請求
     */
    public void get() {
        // 1. 創建一個默認的client實例
        CloseableHttpClient client = HttpClients.createDefault();

        try {
            // 2. 創建一個httpget對象
            HttpGet httpGet = new HttpGet(REQUEST_URL);
            System.out.println("executing GET request " + httpGet.getURI());

            // 3. 執行GET請求並獲取響應對象
            CloseableHttpResponse resp = client.execute(httpGet);

            try {
                // 4. 獲取響應體
                HttpEntity entity = resp.getEntity();
                System.out.println("------");

                // 5. 打印響應狀態
                System.out.println(resp.getStatusLine());

                // 6. 打印響應長度和響應內容
                if (null != entity) {
                    System.out.println("Response content length = " + entity.getContentLength());
                    System.out.println("Response content is:\n" + EntityUtils.toString(entity));
                }

                System.out.println("------");
            } finally {
                // 7. 無論請求成功與否都要關閉resp
                resp.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 8. 最終要關閉連接，釋放資源
            try {
                client.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 測試發送POST請求
     */
    public void post() {
        // 1. 獲取默認的client實例
        CloseableHttpClient client = HttpClients.createDefault();
        // 2. 創建httppost實例
        HttpPost httpPost = new HttpPost(REQUEST_URL);
        // 3. 創建參數隊列（鍵值對列表）
        List<NameValuePair> paramPairs = new ArrayList<NameValuePair>();
        paramPairs.add(new BasicNameValuePair("username", "admin"));
        paramPairs.add(new BasicNameValuePair("password", "123456"));

        UrlEncodedFormEntity entity;

        try {
            // 4. 將參數設置到entity對象中
            entity = new UrlEncodedFormEntity(paramPairs, "UTF-8");

            // 5. 將entity對象設置到httppost對象中
            httpPost.setEntity(entity);

            System.out.println("executing POST request " + httpPost.getURI());

            // 6. 發送請求並回去響應
            CloseableHttpResponse resp = client.execute(httpPost);

            try {
                // 7. 獲取響應entity
                HttpEntity respEntity = resp.getEntity();

                // 8. 打印出響應內容
                if (null != respEntity) {
                    System.out.println("------");
                    System.out.println(resp.getStatusLine());
                    System.out.println("Response content is : \n" + EntityUtils.toString(respEntity, "UTF-8"));

                    System.out.println("------");
                }
            } finally {
                // 9. 關閉響應對象
                resp.close();
            }

        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 10. 關閉連接，釋放資源
            try {
                client.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        HttpClientTest test = new HttpClientTest();
        // 測試GET請求
        test.get();
        // 測試POST請求
        test.post();
    }
}

 

2、輸出結果：

executing GET request http://localhost:8080/TomcatTest/hello
------
HTTP/1.1 200 OK
Response content length = 34
Response content is:
Hello world! 你好，世界！！
------
executing POST request http://localhost:8080/TomcatTest/hello
------
HTTP/1.1 200 OK
Response content is :
your username is:admin
your password is:123456
------

 

 （四）jar包下載

所需jar包打包下載地址：https://pan.baidu.com/s/1mhJ9iT6