Java學習筆記 31 - 使用HTTP協(xié)議發(fā)送GET/POST請求(詳細)

使用HTTP協(xié)議發(fā)送GET/POST請求，可以有多種方式，以下詳細介紹兩種方法。
一、JDK 的 java.net 包中提供的訪問 HTTP 協(xié)議功能發(fā)送GET/POST請求
1、發(fā)送get請求詳細步驟
1)創(chuàng)建要請求的URL實例

            String urlNameString = url + "?" + param;
            URL realUrl = new URL(urlNameString);

2)打開和實例URL的連接

            URLConnection connection = realUrl.openConnection();

3)為已打開的連接設置HTTP請求通用的屬性,如accept,connection,user-agent.

            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");

4)在設置好屬性的連接基礎(chǔ)上,執(zhí)行實際的連接,即發(fā)送請求

            connection.connect();

5)獲取get請求的響應頭

            Map<String, List<String>> map = connection.getHeaderFields();
             // 遍歷所有的響應頭字段
             for (String key : map.keySet()) {
                System.out.println(key + "--->" + map.get(key));
              }

6)獲取get請求的響應結(jié)果.這里可以通過BufferedReader輸入流來讀取URL的響應

             BufferedReader in = new BufferedReader(new InputStreamReader(
                    connection.getInputStream()));
             String line;
             while ((line = in.readLine()) != null) {
                result += line;
              }

也可以使用工具類IOUtils的toString方法獲取響應結(jié)果.

              result = IOUtils.toString(connection.getInputStream(),"utf-8");

7)關(guān)閉流,關(guān)閉連接

   // 使用finally塊來關(guān)閉輸入流
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (Exception e2) {
                e2.printStackTrace();
            }
        }

2、發(fā)送post請求詳細步驟
1)創(chuàng)建要請求的URL實例

            String urlNameString = url + "?" + param;
            URL realUrl = new URL(urlNameString);

2)打開和實例URL的連接

            URLConnection connection = realUrl.openConnection();

3)為已打開的連接設置HTTP請求通用的屬性,如accept,connection,user-agent.

            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");

4)由于post請求,參數(shù)是放在body中,需要設置連接中允許寫入?yún)?shù)

        conn.setDoOutput(true);
            conn.setDoInput(true);

5)獲取URLConnection對象對應的輸出流

         PrintWriter out = new PrintWriter(conn.getOutputStream());

6)寫入發(fā)送post請求需要的參數(shù)

         out.print(param);
             out.flush();

6)獲取get請求的響應結(jié)果.這里可以通過BufferedReader輸入流來讀取URL的響應

             BufferedReader in = new BufferedReader(new InputStreamReader(
                    connection.getInputStream()));
             String line;
             while ((line = in.readLine()) != null) {
                result += line;
              }

    也可以使用工具類IOUtils的toString方法獲取響應結(jié)果.

           List<String> list = IOUtils.readLines(conn.getInputStream(),"UTF-8");
            for(String s:list){
                System.out.println(s);
            }

7)關(guān)閉流,關(guān)閉連接

完整代碼：

package com.sc.http;

import org.apache.commons.io.IOUtils;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;

public class HttpRequest {
    /**
     * 向指定URL發(fā)送GET方法的請求
     *
     * @param url
     *            發(fā)送請求的URL
     * @param param
     *            請求參數(shù)，請求參數(shù)應該是 name1=value1&name2=value2 的形式。
     * @return URL 所代表遠程資源的響應結(jié)果
     */
    public static String sendGet(String url, String param) {
        String result = "";
        BufferedReader in = null;
        try {
            String urlNameString = url + "?" + param;
            URL realUrl = new URL(urlNameString);
            // 打開和URL之間的連接
            URLConnection connection = realUrl.openConnection();
            // 設置通用的請求屬性
            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 建立實際的連接
            connection.connect();
            // 獲取所有響應頭字段
            Map<String, List<String>> map = connection.getHeaderFields();
            // 遍歷所有的響應頭字段
            for (String key : map.keySet()) {
                System.out.println(key + "--->" + map.get(key));
            }
             //定義 BufferedReader輸入流來讀取URL的響應
            in = new BufferedReader(new InputStreamReader(
                    connection.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }

            result = IOUtils.toString(connection.getInputStream(),"utf-8");
        } catch (Exception e) {
            System.out.println("發(fā)送GET請求出現(xiàn)異常！" + e);
            e.printStackTrace();
        }
        // 使用finally塊來關(guān)閉輸入流
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (Exception e2) {
                e2.printStackTrace();
            }
        }
        return result;
    }

    /**
     * 向指定 URL 發(fā)送POST方法的請求
     *
     * @param url
     *            發(fā)送請求的 URL
     * @param param
     *            請求參數(shù)，請求參數(shù)應該是 name1=value1&name2=value2 的形式。
     * @return 所代表遠程資源的響應結(jié)果
     */
    public static String sendPost(String url, String param) {
        PrintWriter out = null;
        BufferedReader in = null;
        String result = "";
        try {
            URL realUrl = new URL(url);
            // 打開和URL之間的連接
            URLConnection conn = realUrl.openConnection();
            // 設置通用的請求屬性
            conn.setRequestProperty("accept", "*/*");
            conn.setRequestProperty("connection", "Keep-Alive");
            conn.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 發(fā)送POST請求必須設置如下兩行
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 獲取URLConnection對象對應的輸出流
            out = new PrintWriter(conn.getOutputStream());
            // 發(fā)送請求參數(shù)
            out.print(param);
            // flush輸出流的緩沖
            out.flush();
            // 定義BufferedReader輸入流來讀取URL的響應
            in = new BufferedReader(
                    new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
//            List<String> list = IOUtils.readLines(conn.getInputStream(),"UTF-8");
//            for(String s:list){
//                System.out.println(s);
//            }
        } catch (Exception e) {
            System.out.println("發(fā)送 POST 請求出現(xiàn)異常！"+e);
            e.printStackTrace();
        }
        //使用finally塊來關(guān)閉輸出流、輸入流
        finally{
            try{
                if(out!=null){
                    out.close();
                }
                if(in!=null){
                    in.close();
                }
            }
            catch(Exception ex){
                ex.printStackTrace();
            }
        }
        return result;
    }

    public static void main(String[] args) {
        //發(fā)送 GET 請求
//        String s=HttpRequest.sendGet("http://www.baidu.com", "key=123&v=456");
//        System.out.println(s);

        //發(fā)送 POST 請求
        String sr=HttpRequest.sendPost("http://192.168.200.66/zabbix/screens.php", "ddreset=1");
        System.out.println(sr);
    }
}

二、使用org.apache.http包下的HttpClient發(fā)送GET/POST請求
HttpClient相比傳統(tǒng)JDK自帶的URLConnection，增加了易用性和靈活性。它不僅是客戶端發(fā)送Http請求變得容易，而且也方便了開發(fā)人員測試接口（基于Http協(xié)議的），即提高了開發(fā)的效率，也方便提高代碼的健壯性。
1、HttpClient發(fā)送get請求(無參數(shù))詳細步驟
1). 創(chuàng)建HttpClient對象

            CloseableHttpClient httpclient = HttpClients.createDefault();

2). 創(chuàng)建請求方法的實例，并指定請求URL

            HttpGet get = new HttpGet("http://www.baidu.com");

3). 調(diào)用HttpClient對象的execute(HttpUriRequest request)發(fā)送請求，該方法返回一個HttpResponse。

            CloseableHttpResponse response= httpclient.execute(get);

4).獲取get請求的響應結(jié)果.調(diào)用HttpResponse的getEntity()方法可獲取HttpEntity對象，該對象包裝了服務器的響應內(nèi)容

            HttpEntity entity = response.getEntity();

獲取響應狀態(tài)

 int code = response.getStatusLine().getStatusCode();
 System.out.println(" code "+code);

5).通過BufferedReader輸入流讀取響應結(jié)果

            BufferedReader  in = new BufferedReader(
                    new InputStreamReader(entity.getContent(),"UTF-8"));
            String line;
            String result="";
            while ((line = in.readLine()) != null) {
                result += line+"\n";
            }
            System.out.println(result);

  可以使用工具類IOUtils的toString方法獲取響應結(jié)果.

           List<String> list = IOUtils.readLines(entity.getContent(),"UTF-8");
            for(String s:list){
                System.out.println(s);
            }

   或者：

      result=IOUtils.toString(entity.getContent(),"utf-8");

   可以使用EntityUtils的toString方法獲取響應結(jié)果.(推薦使用)

           if(entity!=null){
                System.out.println(EntityUtils.toString(entity));
            }

6).釋放連接,無論執(zhí)行方法是否成功，都必須釋放連接
完整代碼：

package com.sc.http;
import java.io.IOException;
import org.apache.http.HttpEntity;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpClientTest2 {

    public static void main(String[] args)  {
        CloseableHttpClient httpclient = HttpClients.createDefault();

        CloseableHttpResponse response = null;
        HttpEntity  entity=null;
        try {
            HttpGet get = new HttpGet("http://www.baidu.com");
            response = httpclient.execute(get);
            entity = response.getEntity();
            int code = response.getStatusLine().getStatusCode();
            System.out.println(" code "+code);
            if(entity!=null){
                System.out.println(EntityUtils.toString(entity));
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                EntityUtils.consume(entity);
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

2、HttpClient發(fā)送post請求詳細步驟
1). 創(chuàng)建HttpClient對象

            CloseableHttpClient httpclient = HttpClients.createDefault();

2). 創(chuàng)建請求方法的實例，并指定請求URL

            HttpPost post = new HttpPost("http://123.58.251.183:8080/goods/UserServlet");

3). 創(chuàng)建HttpEntity,模擬一個表單,用于包裝參數(shù)
POST請求,參數(shù)是放在body內(nèi),所以需要構(gòu)建UrlEncodedFormEntity
而UrlEncodedFormEntity需要傳入的參數(shù)類型為List且List中裝入的是NameValuePair類型的集合
NameValuePair是一個接口,它的實現(xiàn)類是BasicNameValuePair
BasicNameValuePair類的構(gòu)造方法中需要傳入兩個參數(shù)key,value

            List<NameValuePair> list = new ArrayList<NameValuePair>();
            list.add(new BasicNameValuePair("method","loginMobile"));
            list.add(new BasicNameValuePair("loginname","abc"));
            list.add(new BasicNameValuePair("loginpass","abc"));
            HttpEntity postEntity = new UrlEncodedFormEntity(list);
            post.setEntity(postEntity);

4). 若需要使用例如Fidder工具抓包,就需要設置代理.(無需抓包時,可省略此步)

            HttpHost proxy = new HttpHost("127.0.0.1", 8888, "http");
            RequestConfig config = RequestConfig.custom().setProxy(proxy).build();
            post.setConfig(config);

5). 調(diào)用HttpClient對象的execute(HttpUriRequest request)發(fā)送請求，該方法返回一個HttpResponse。

            CloseableHttpResponse response= httpclient.execute(get);

6).獲取get請求的響應結(jié)果.調(diào)用HttpResponse的getEntity()方法可獲取HttpEntity對象，該對象包裝了服務器的響應內(nèi)容

            HttpEntity entity = response.getEntity();

獲取響應狀態(tài)

 int code = response.getStatusLine().getStatusCode();
 System.out.println(" code "+code);

7).通過BufferedReader輸入流讀取響應結(jié)果

            BufferedReader  in = new BufferedReader(
                    new InputStreamReader(entity.getContent(),"UTF-8"));
            String line;
            String result="";
            while ((line = in.readLine()) != null) {
                result += line+"\n";
            }
            System.out.println(result);

  可以使用工具類IOUtils的toString方法獲取響應結(jié)果.

           List<String> list = IOUtils.readLines(entity.getContent(),"UTF-8");
            for(String s:list){
                System.out.println(s);
            }

   或者：

          result=IOUtils.toString(entity.getContent(),"utf-8");

   可以使用EntityUtils的toString方法獲取響應結(jié)果.(推薦使用)

           if(entity!=null){
                System.out.println(EntityUtils.toString(entity));
            }

8).釋放連接,無論執(zhí)行方法是否成功，都必須釋放連接

        EntityUtils.consume(httpEntity);
            closeableHttpClient.close();

完整代碼：

package com.sc.http;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.NameValuePair;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
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;

public class HttpClientTest3 {

    public static void main(String[] args) {
        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        HttpPost post = new HttpPost("http://123.58.251.183:8080/goods/UserServlet");
        List<NameValuePair> list = new ArrayList<NameValuePair>();
        list.add(new BasicNameValuePair("method","loginMobile"));
        list.add(new BasicNameValuePair("loginname","abc"));
        list.add(new BasicNameValuePair("loginpass","abc"));

         HttpHost proxy = new HttpHost("127.0.0.1", 8888, "http");
          RequestConfig config = RequestConfig.custom().setProxy(proxy).build();

        HttpEntity httpEntity = null;
        try {
            HttpEntity postEntity = new UrlEncodedFormEntity(list);
            post.setEntity(postEntity);
            //post.setConfig(config);

            CloseableHttpResponse reponse = closeableHttpClient.execute(post);
            httpEntity= reponse.getEntity();
            System.out.println(EntityUtils.toString(httpEntity, "utf-8"));
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                EntityUtils.consume(httpEntity);
                closeableHttpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}
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