HttpClient使用詳解

Http協議的重要性相信不用我多說了，HttpClient相比傳統JDK自帶的URLConnection，增加了易用性和靈活性（具體區別，日後我們再討論），它不僅是客戶端發送Http請求變得容易，而且也方便了開發人員測試接口（基於Http協議的），即提高了開發的效率，也方便提高代碼的健壯性。因此熟練掌握HttpClient是很重要的必修內容，掌握HttpClient後，相信對於Http協議的瞭解會更加深入。

一、簡介

HttpClient是Apache Jakarta Common下的子項目，用來提供高效的、最新的、功能豐富的支持HTTP協議的客戶端編程工具包，並且它支持HTTP協議最新的版本和建議。HttpClient已經應用在很多的項目中，比如Apache Jakarta上很著名的另外兩個開源項目Cactus和HTMLUnit都使用了HttpClient。

下載地址: http://hc.apache.org/downloads.cgi

二、特性

1. 基於標準、純淨的Java語言。實現了Http1.0和Http1.1

2. 以可擴展的面向對象的結構實現了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。

3. 支持HTTPS協議。

4. 通過Http代理建立透明的連接。

5. 利用CONNECT方法通過Http代理建立隧道的https連接。

6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos認證方案。

7. 插件式的自定義認證方案。

8. 便攜可靠的套接字工廠使它更容易的使用第三方解決方案。

9. 連接管理器支持多線程應用。支持設置最大連接數，同時支持設置每個主機的最大連接數，發現並關閉過期的連接。

10. 自動處理Set-Cookie中的Cookie。

11. 插件式的自定義Cookie策略。

12. Request的輸出流可以避免流中內容直接緩衝到socket服務器。

13. Response的輸入流可以有效的從socket服務器直接讀取相應內容。

14. 在http1.0和http1.1中利用KeepAlive保持持久連接。

15. 直接獲取服務器發送的response code和 headers。

16. 設置連接超時的能力。

17. 實驗性的支持http1.1 response caching。

18. 源代碼基於Apache License 可免費獲取。

三、使用方法

使用HttpClient發送請求、接收響應很簡單，一般需要如下幾步即可。

1. 創建HttpClient對象。

2. 創建請求方法的實例，並指定請求URL。如果需要發送GET請求，創建HttpGet對象；如果需要發送POST請求，創建HttpPost對象。

3. 如果需要發送請求參數，可調用HttpGet、HttpPost共同的setParams(HetpParams params)方法來添加請求參數；對於HttpPost對象而言，也可調用setEntity(HttpEntity entity)方法來設置請求參數。

4. 調用HttpClient對象的execute(HttpUriRequest request)發送請求，該方法返回一個HttpResponse。

5. 調用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可獲取服務器的響應頭；調用HttpResponse的getEntity()方法可獲取HttpEntity對象，該對象包裝了服務器的響應內容。程序可通過該對象獲取服務器的響應內容。

6. 釋放連接。無論執行方法是否成功，都必須釋放連接

四、實例

package com.test;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.KeyManagementException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateException;
import java.util.ArrayList;
import java.util.List;

import javax.net.ssl.SSLContext;

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.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.conn.ssl.SSLContexts;
import org.apache.http.conn.ssl.TrustSelfSignedStrategy;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.entity.mime.content.StringBody;
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;
import org.junit.Test;

public class HttpClientTest {

    @Test
    public void jUnitTest() {
        get();
    }

    /**
     * HttpClient連接SSL
     */
    public void ssl() {
        CloseableHttpClient httpclient = null;
        try {
            KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
            FileInputStream instream = new FileInputStream(new File("d:\\tomcat.keystore"));
            try {
                // 加載keyStore d:\\tomcat.keystore
                trustStore.load(instream, "123456".toCharArray());
            } catch (CertificateException e) {
                e.printStackTrace();
            } finally {
                try {
                    instream.close();
                } catch (Exception ignore) {
                }
            }
            // 相信自己的CA和所有自簽名的證書
            SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build();
            // 只允許使用TLSv1協議
            SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,
                    SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);
            httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();
            // 創建http請求(get方式)
            HttpGet httpget = new HttpGet("https://localhost:8443/myDemo/Ajax/serivceJ.action");
            System.out.println("executing request" + httpget.getRequestLine());
            CloseableHttpResponse response = httpclient.execute(httpget);
            try {
                HttpEntity entity = response.getEntity();
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                if (entity != null) {
                    System.out.println("Response content length: " + entity.getContentLength());
                    System.out.println(EntityUtils.toString(entity));
                    EntityUtils.consume(entity);
                }
            } finally {
                response.close();
            }
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (KeyManagementException e) {
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (KeyStoreException e) {
            e.printStackTrace();
        } finally {
            if (httpclient != null) {
                try {
                    httpclient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * post方式提交表單（模擬用戶登錄請求）
     */
    public void postForm() {
        // 創建默認的httpClient實例.
        CloseableHttpClient httpclient = HttpClients.createDefault();
        // 創建httppost
        HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");
        // 創建參數隊列
        List<namevaluepair> formparams = new ArrayList<namevaluepair>();
        formparams.add(new BasicNameValuePair("username", "admin"));
        formparams.add(new BasicNameValuePair("password", "123456"));
        UrlEncodedFormEntity uefEntity;
        try {
            uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");
            httppost.setEntity(uefEntity);
            System.out.println("executing request " + httppost.getURI());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    System.out.println("--------------------------------------");
                    System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));
                    System.out.println("--------------------------------------");
                }
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e1) {
            e1.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 關閉連接,釋放資源
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 發送 post請求訪問本地應用並根據傳遞參數不同返回不同結果
     */
    public void post() {
        // 創建默認的httpClient實例.
        CloseableHttpClient httpclient = HttpClients.createDefault();
        // 創建httppost
        HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");
        // 創建參數隊列
        List<namevaluepair> formparams = new ArrayList<namevaluepair>();
        formparams.add(new BasicNameValuePair("type", "house"));
        UrlEncodedFormEntity uefEntity;
        try {
            uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");
            httppost.setEntity(uefEntity);
            System.out.println("executing request " + httppost.getURI());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    System.out.println("--------------------------------------");
                    System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));
                    System.out.println("--------------------------------------");
                }
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e1) {
            e1.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 關閉連接,釋放資源
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 發送 get請求
     */
    public void get() {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            // 創建httpget.
            HttpGet httpget = new HttpGet("http://www.baidu.com/");
            System.out.println("executing request " + httpget.getURI());
            // 執行get請求.
            CloseableHttpResponse response = httpclient.execute(httpget);
            try {
                // 獲取響應實體
                HttpEntity entity = response.getEntity();
                System.out.println("--------------------------------------");
                // 打印響應狀態
                System.out.println(response.getStatusLine());
                if (entity != null) {
                    // 打印響應內容長度
                    System.out.println("Response content length: " + entity.getContentLength());
                    // 打印響應內容
                    System.out.println("Response content: " + EntityUtils.toString(entity));
                }
                System.out.println("------------------------------------");
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 關閉連接,釋放資源
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 上傳文件
     */
    public void upload() {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceFile.action");

            FileBody bin = new FileBody(new File("F:\\image\\sendpix0.jpg"));
            StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);

            HttpEntity reqEntity = MultipartEntityBuilder.create().addPart("bin", bin).addPart("comment", comment).build();

            httppost.setEntity(reqEntity);

            System.out.println("executing request " + httppost.getRequestLine());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                HttpEntity resEntity = response.getEntity();
                if (resEntity != null) {
                    System.out.println("Response content length: " + resEntity.getContentLength());
                }
                EntityUtils.consume(resEntity);
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}</namevaluepair></namevaluepair></namevaluepair></namevaluepair>

本實例是採用HttpClient4.3最新版本。該版本與之前的代碼寫法風格相差較大，大家多留意下。