HttpClient 4.5使用(一)

一开始上手就用4.5有的不大习惯，看到的教程和分享都是4.5之前的，这个纪录主要是把掉过的坑都记住。

1.HttpGet返回网页信息

package cn.limbo.grabdata.test;import org.apache.http.HttpEntity;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 java.io.IOException;import java.io.InputStream;/** * Created by Limbo on 16/7/28. */public class TestHttpClient {    public static void main(String[] args) {        //4.x版本貌似HttpClient就成了一个接口了        //现在都用这个来创建客户端连接,相当于打开了一个浏览器        CloseableHttpClient httpClient = HttpClients.createDefault();        //以前的名字叫做GetMethod,现在改名为HttpGet        HttpGet httpGet = new HttpGet("http://www.baidu.com");        //返回请求信息        System.out.println("Executing request" + httpGet.getRequestLine());        //创建一个返回信息的对象        CloseableHttpResponse response = null;        try {            response = httpClient.execute(httpGet);            try {                System.out.println("-------------------");                //打印返回状态                System.out.println(response.getStatusLine());                //实体                HttpEntity httpEntity = response.getEntity();                if (httpEntity != null) {                    InputStream inputStream = httpEntity.getContent();                    try {                        inputStream.read();                    } catch (IOException ex) {                        throw ex;                    } finally {                        inputStream.close();                    }                }            } catch (IOException e) {                e.printStackTrace();            }finally {                response.close();            }        } catch (IOException e) {            e.printStackTrace();        } finally {            try {                httpClient.close();            } catch (IOException e) {                e.printStackTrace();            }        }    }}

2.HttpGet

package cn.limbo.grabdata.test;import org.apache.http.HttpEntity;import org.apache.http.HttpResponse;import org.apache.http.NameValuePair;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.impl.conn.DefaultHttpClientConnectionOperator;import org.apache.http.message.BasicNameValuePair;import org.apache.http.protocol.HTTP;import org.apache.http.util.EntityUtils;import java.io.IOException;import java.nio.charset.StandardCharsets;import java.util.ArrayList;import java.util.List;/** * Created by Limbo on 16/7/29. */public class TestPost {    public static void main(String[] args) {        CloseableHttpClient client = HttpClients.createDefault();        try {            //一定要加上http否则会报 Target host is not specified            HttpPost httpPost = new HttpPost("http://www.baidu.com");            //设置HttpPost的传参数            List<NameValuePair> params = new ArrayList<>();            params.add(new BasicNameValuePair("post", "I will post"));            //由于JDK7出现,HTTP中的很多编码被标识成了过期,使用StandardCharsets里面的预定义的东西            httpPost.setEntity(new UrlEncodedFormEntity(params, StandardCharsets.UTF_8));            CloseableHttpResponse response = client.execute(httpPost);            int statusCode = response.getStatusLine().getStatusCode();            System.out.println("statusCode : " + statusCode);            String responseStr = null;            HttpEntity httpEntity = response.getEntity();            if (httpEntity != null) {                responseStr = EntityUtils.toString(httpEntity, StandardCharsets.UTF_8);            }            System.out.println("respStr = " + responseStr);            //释放资源            EntityUtils.consume(httpEntity);        } catch (IOException e) {            e.printStackTrace();        }    }}

3.补充

1.需要向服务器发送请求，我们需要一个org.apache.http.client.HttpClient的实例对象，一般使用的都是org.apache.http.impl.client.CloseableHttpClient，创建该对象的最简单方法是CloseableHttpClient client = HttpClients.createDefault();,HttpClients是负责创建CloseableHttpClient的工厂，现在我们用最简单的方法就是使用默认配置去创建实例，后面我们再讨论有参数定制需求的实例创建方法。我们可以通过打断点的方式看到这个默认的实例对象的连接管理器 ： org.apache.http.conn.HttpClientConnectionManager、请求配置 ：org.apache.http.client.config.RequestConfig等配置的默认参数，这些都是后面需要了解的。

2.构造请求方法HttpPost post = new HttpPost(url);表示我们希望用那种交互方法与服务器交互，HttpClient为每种交互方法都提供了一个类：HttpGet,
HttpHead, HttpPost, HttpPut, HttpDelete, HttpTrace, 还有 HttpOptions。

3.向服务器提交请求CloseableHttpResponse response = client.execute(post);，很明显`CloseableHttpResponse就是用了处理返回数据的实体，通过它我们可以拿到返回的状态码、返回实体等等我们需要的东西。

4.EntityUtils是官方提供一个处理返回实体的工具类，toString方法负责将返回实体装换为字符串，官方是不太建议使用这个类的，除非返回数据的服务器绝对可信和返回的内容长度是有限的。官方建议是自己使用HttpEntity#getContent()或者HttpEntity#writeTo(OutputStream)，需要提醒的是记得关闭底层资源。

5.EntityUtils.consume(entity);负责释放资源，通过源码可知，是需要把底层的流关闭：

InputStream instream = entity.getContent();if (instream != null) {    instream.close();}