HttpClient学习

 HttpClient学习

（1）下面列举几个主要的Http相关概念的类

类名	描述
HttpClient	建立请求客户端
HttpGet	代表请求方法，类似的还有HttpHead, HttpPost, HttpPut, HttpDelete, HttpTrace,  HttpOptions等
HttpResponse	表示请求的响应（包括响应状态、协议等头信息，Header封装各种头信息，头信息又包括HeaderElement，都可以采用迭代器的方式进行迭代读取）
HttpEntity	表示相应的实体，用于存放传送的内容，也就是body体，存在于request和response中，request只有post和put方法有，response中都有Entity，除了一些特殊情况不包含内容。Entity根据来源分为三种：streamed，一次读取；wrapping，从其他entity封装；self-contained，从内存中读取，可反复读。
URIBuilder	工具类用来生成url，主要是设置协议、域名和路径，还有各种参数等

（2）HttpEntity的几个主要函数

函数	描述
getContentType	获取内容类型
getContentLength	获取内容长度
getContent	获取内容的输入流InputStream

 

HttpEntity entity=response.getEntity();

            System.out.println(entity.getContentType());

            System.out.println(entity.getContentLength());

            InputStream in=entity.getContent();//直接获取输入流，一次读取

（3）HttpEntity直接获取的streamed流

只能读取一次，如果想读取多次，就要进行缓存，利用wrapping方式将streamed进行包装BufferedHttpEntity
BufferedHttpEntity bufEntity=new BufferedHttpEntity(entity);//通过构造形式封装进缓存，可多次读取

（4）HttpEntity也可放在post和put方法的请求中

作为请求传递的内容。内容可以是文件，也可以提交form参数
            File file=new File("out.txt");

            FileEntity fileEntity=new FileEntity(file, ContentType.create("text/plain", "UTF-8"));//文件内容输入



            List formparams = new ArrayList();

            formparams.add(new BasicNameValuePair("param1", "value1"));

            formparams.add(new BasicNameValuePair("param2", "value2"));

            UrlEncodedFormEntity formEntity = new UrlEncodedFormEntity(formparams, "UTF-8");//form表单内容输入

            HttpPost post=new HttpPost("http://www.baidu.com");

            post.setEntity(fileEntity);

（5）response处理类最方便的是ResponseHandler类，它的功能是将entity转化为不同的内容格式

ResponseHandler<byte[]> handler = new ResponseHandler<byte[]>() {

              public byte[] handleResponse(

                       HttpResponse response) throws ClientProtocolException, IOException {

                   HttpEntity entity = response.getEntity();

                  if (entity != null) {

                      return EntityUtils.toByteArray(entity);

                  } else {

                      return null;

                  }

              }

          };



          byte[] response = httpclient.execute(httpget, handler);

           ResponseHandler handler1=new BasicResponseHandler();

           String response1= httpclient.execute(httpget,handler1);

（6）request请求时可以设置一些http参数httpparam

和httpcontext相似，httpclient可以设置客户端范围的，httprequest也可以设置，但是请求范围的。

参数名	描述
CoreProtocolPNames.PROTOCOL_VERSION='http.protocol.version'	协议版本
CoreProtocolPNames.HTTP_ELEMENT_CHARSET='http.protocol.element-charset'	协议元素编码
CoreProtocolPNames.HTTP_CONTENT_CHARSET='http.protocol.content-charset'	协议内容编码
CoreProtocolPNames.USER_AGENT='http.useragent'	用户端，写爬虫的时候有用
CoreProtocolPNames.STRICT_TRANSFER_ENCODING='http.protocol.strict-transfer-encoding'	(...
CoreProtocolPNames.USE_EXPECT_CONTINUE='http.protocol.expect-continue'	...
CoreProtocolPNames.WAIT_FOR_CONTINUE='http.protocol.wait-for-continue'	...

 

httpclient.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION,

  HttpVersion.HTTP_1_0); // Default to HTTP 1.0

  httpclient.getParams().setParameter(CoreProtocolPNames.HTTP_CONTENT_CHARSET,

     "UTF-8");



  HttpGet httpget = new HttpGet("http://www.google.com.hk/");

  httpget.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION,

      HttpVersion.HTTP_1_1); // Use HTTP 1.1 for this request only

  httpget.getParams().setParameter(CoreProtocolPNames.USE_EXPECT_CONTINUE,

      Boolean.FALSE);

（7）httpclient完成了对connection的控制

但是上面的方法都没有涉及连接的设置，这里提供一些参数可以进行设置通过HttpParam设置

参数	描述
CoreConnectionPNames.SO_TIMEOUT='http.socket.timeout'	等待数据的最大时间，也就是两段连续数据读取之间的间隔
CoreConnectionPNames.TCP_NODELAY='http.tcp.nodelay'	bool值，设置是否应用Naple算法，该算法最小化发送的包数，因此每个包很大，占带宽，有延迟
CoreConnectionPNames.SOCKET_BUFFER_SIZE='http.socket.buffer-size'	设置接发数据的缓冲区大小
CoreConnectionPNames.SO_LINGER='http.socket.linger'	...
CoreConnectionPNames.CONNECTION_TIMEOUT='http.connection.timeout'	设置连接超时
CoreConnectionPNames.STALE_CONNECTION_CHECK='http.connection.stalecheck'	...
CoreConnectionPNames.MAX_LINE_LENGTH='http.connection.max-line-length'	设置每行最大长度
CoreConnectionPNames.MAX_HEADER_COUNT='http.connection.max-header-count'	设置头最大数量
ConnConnectionPNames.MAX_STATUS_LINE_GARBAGE='http.connection.max-status-line-garbage'	...

（8）实际应用的中，从连接池里获取连接是比较好的方法，连接池负责管理连接。

BasicClientConnectionManager man=new BasicClientConnectionManager();//最基本的连接池，一次只维护一个连接

System.out.println(httpclient.getConnectionManager().getClass());//输出class org.apache.http.impl.conn.BasicClientConnectionManager



//下面采用PoolingClientConnectionManager连接池管理，该连接池支持多线程操作

   if(httpConnManger==null)

  {

     SchemeRegistry schemeRegistry = new SchemeRegistry();

     schemeRegistry.register(

  new Scheme("http", 80, PlainSocketFactory.getSocketFactory()));

   httpConnManger=new PoolingClientConnectionManager(schemeRegistry);

   httpConnManger.setMaxTotal(10);

   httpConnManger.setDefaultMaxPerRoute(20);

}

 HttpParams params=new BasicHttpParams();

 params.setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, CONNECTION_TIME);

 HttpClient httpClient=new DefaultHttpClient(httpConnManger,params);

 HttpGet httpGet=new HttpGet(urlAddr);

 HttpResponse response;

try {

  response = httpClient.execute(httpGet);

} catch (ClientProtocolException e) {

  log.error(e.getMessage());

 return null;

} catch (IOException e) {

  log.error(e.getMessage());

 return null;

}

（9）需要代理的请求，设置HttpProxy

HttpHost proxy = new HttpHost("127.0.0.1", 8080, "http");

DefaultHttpClient httpclient = new DefaultHttpClient();

httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);

HttpHost target = new HttpHost("issues.apache.org", 443, "https");

HttpGet req = new HttpGet("/");

System.out.println("executing request to " + target + " via " + proxy);

HttpResponse rsp = httpclient.execute(target, req);

HttpEntity entity = rsp.getEntity();

（10）需要登录验证的请求

httpclient.getCredentialsProvider().setCredentials(

                  new AuthScope("localhost", 443),

                  new UsernamePasswordCredentials("username", "password"));



           HttpGet httpget = new HttpGet("https://localhost/protected");



           System.out.println("executing request" + httpget.getRequestLine());

           HttpResponse response = httpclient.execute(httpget);

           HttpEntity entity = response.getEntity();



           System.out.println("----------------------------------------");

           System.out.println(response.getStatusLine());

          if (entity != null) {

               System.out.println("Response content length: " + entity.getContentLength());

          }

           EntityUtils.consume(entity);