JAVA的第三方库HttpClient使用详解

一.简介

HttpClient是Apache Jakarta Common下的子项目，用来提供高效的、最新的、功能丰富的支持HTTP协议的客户端编程工具包，并且它支持HTTP协议最新的版本和建议。HttpClient已经应用在很多的项目中，比如Apache Jakarta上很著名的另外两个开源项目Cactus和HTMLUnit都使用了HttpClient。
下载地址:http://hc.apache.org/downloads.cgi

二.特性

1. 基于标准、纯净的Java语言。实现了Http1.0和Http1.1
2. 以可扩展的面向对象的结构实现了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。
3. 支持HTTPS协议。
4. 通过Http代理建立透明的连接。
5. 利用CONNECT方法通过Http代理建立隧道的https连接。
6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos认证方案。
7. 插件式的自定义认证方案。
8. 便携可靠的套接字工厂使它更容易的使用第三方解决方案。
9. 连接管理器支持多线程应用。支持设置最大连接数，同时支持设置每个主机的最大连接数，发现并关闭过期的连接。
10. 自动处理Set-Cookie中的Cookie。
11. 插件式的自定义Cookie策略。
12. Request的输出流可以避免流中内容直接缓冲到socket服务器。
13. Response的输入流可以有效的从socket服务器直接读取相应内容。
14. 在http1.0和http1.1中利用KeepAlive保持持久连接。
15. 直接获取服务器发送的response code和 headers。
16. 设置连接超时的能力。
17. 实验性的支持http1.1 response caching。
18. 源代码基于Apache License 可免费获取。

三.使用方法

使用HttpClient发送请求、接收响应很简单，一般需要如下几步即可。

1. 创建HttpClient对象。
2. 创建请求方法的实例，并指定请求URL。如果需要发送GET请求，创建HttpGet对象；如果需要发送POST请求，创建HttpPost对象。
3. 如果需要发送请求参数，可调用HttpGet、HttpPost共同的setParams(HetpParams params)方法来添加请求参数；对于HttpPost对象而言，也可调用setEntity(HttpEntity entity)方法来设置请求参数。
4. 调用HttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个HttpResponse。
5. 调用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头；调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器的响应内容。程序可通过该对象获取服务器的响应内容。
6. 释放连接。无论执行方法是否成功，都必须释放连接

四.实例

/** 
 * HttpClient连接SSL 
 */  
public void ssl() {  
    CloseableHttpClient httpclient = null;  
    try {  
        KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());  
        FileInputStream instream = new FileInputStream(new File("d:\\tomcat.keystore"));  
        try {  
            // 加载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和所有自签名的证书  
        SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build();  
        // 只允许使用TLSv1协议  
        SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,  
                SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);  
        httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();  
        // 创建http请求(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方式提交表单（模拟用户登录请求） 
 */  
public void postForm() {  
    // 创建默认的httpClient实例.    
    CloseableHttpClient httpclient = HttpClients.createDefault();  
    // 创建httppost    
    HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");  
    // 创建参数队列    
    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 {  
        // 关闭连接,释放资源    
        try {  
            httpclient.close();  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
    }  
}  

/** 
 * 发送 post请求访问本地应用并根据传递参数不同返回不同结果 
 */  
public void post() {  
    // 创建默认的httpClient实例.    
    CloseableHttpClient httpclient = HttpClients.createDefault();  
    // 创建httppost    
    HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");  
    // 创建参数队列    
    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 {  
        // 关闭连接,释放资源    
        try {  
            httpclient.close();  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
    }  
}  

/** 
 * 发送 get请求 
 */  
public void get() {  
    CloseableHttpClient httpclient = HttpClients.createDefault();  
    try {  
        // 创建httpget.    
        HttpGet httpget = new HttpGet("http://www.baidu.com/");  
        System.out.println("executing request " + httpget.getURI());  
        // 执行get请求.    
        CloseableHttpResponse response = httpclient.execute(httpget);  
        try {  
            // 获取响应实体    
            HttpEntity entity = response.getEntity();  
            System.out.println("--------------------------------------");  
            // 打印响应状态    
            System.out.println(response.getStatusLine());  
            if (entity != null) {  
                // 打印响应内容长度    
                System.out.println("Response content length: " + entity.getContentLength());  
                // 打印响应内容    
                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 {  
        // 关闭连接,释放资源    
        try {  
            httpclient.close();  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
    }  
}  

/** 
 * 上传文件 
 */  
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();  
        }  
    }  
}