简介
HttpClient是Apache的一个开源库，相比于JDK自带的URLConnection等，使用起来更灵活方便。
使用方法可以大致分为如下八步曲：
- 创建一个HttpClient对象;
- 创建一个Http请求对象并设置请求的URL，比如GET请求就创建一个HttpGet对象，POST请求就创建一个HttpPost对象;
- 如果需要可以设置请求对象的请求头参数，也可以往请求对象中添加请求参数;
- 调用HttpClient对象的
execute方法执行请求; - 获取请求响应对象和响应Entity;
- 从响应对象中获取响应状态，从响应Entity中获取响应内容;
- 关闭响应对象;
- 关闭HttpClient.
在本地创建一个Servlet程序
在本地创建一个Servlet程序并跑在Tomcat服务器中，主要用于下一步测试HttpClient发送请求。
注：Servlet的创建方法详见：Eclipse+Tomcat搭建本地服务器并跑通HelloWorld程序
- Servlet类：
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class HelloWorld extends HttpServlet {
private static final long serialVersionUID = 4601029764222607869L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
// 1. 设置编码格式
resp.setContentType("text/html");
resp.setCharacterEncoding("UTF-8");
// 2. 往返回体中写返回数据
PrintWriter writer = null;
try {
writer = resp.getWriter();
writer.print("Hello world! 你好，世界！！");
} catch (Exception e) {
e.printStackTrace();
} finally {
writer.close();
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
// 1. 获取请求的参数
String userName = req.getParameter("username");
String password = req.getParameter("password");
// 2. 往返回体写返回数据
PrintWriter writer = null;
try {
writer = resp.getWriter();
writer.print("your username is:" + userName + "\nyour password is:" + password);
} catch (Exception e) {
e.printStackTrace();
} finally {
writer.close();
}
}
}
-
web.xml（新加内容）：
<servlet>
<servlet-name>helloWorld</servlet-name>
<servlet-class>com.servlet.HelloWorld</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>helloWorld</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
测试HttpClient发送GET和POST请求
-
HttpClient测试类：
package com.test.method;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;
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.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
/**
* 测试HttpClient发送各种请求的方法
*
* @author Administrator
*
*/
public class HttpClientTest {
// 发送请求的url
public static final String REQUEST_URL = "http://localhost:8080/TomcatTest/hello";
/**
* 测试发送GET请求
*/
public void get() {
// 1. 创建一个默认的client实例
CloseableHttpClient client = HttpClients.createDefault();
try {
// 2. 创建一个httpget对象
HttpGet httpGet = new HttpGet(REQUEST_URL);
System.out.println("executing GET request " + httpGet.getURI());
// 3. 执行GET请求并获取响应对象
CloseableHttpResponse resp = client.execute(httpGet);
try {
// 4. 获取响应体
HttpEntity entity = resp.getEntity();
System.out.println("------");
// 5. 打印响应状态
System.out.println(resp.getStatusLine());
// 6. 打印响应长度和响应内容
if (null != entity) {
System.out.println("Response content length = " + entity.getContentLength());
System.out.println("Response content is:\n" + EntityUtils.toString(entity));
}
System.out.println("------");
} finally {
// 7. 无论请求成功与否都要关闭resp
resp.close();
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (ParseException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
// 8. 最终要关闭连接，释放资源
try {
client.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
/**
* 测试发送POST请求
*/
public void post() {
// 1. 获取默认的client实例
CloseableHttpClient client = HttpClients.createDefault();
// 2. 创建httppost实例
HttpPost httpPost = new HttpPost(REQUEST_URL);
// 3. 创建参数队列（键值对列表）
List<NameValuePair> paramPairs = new ArrayList<NameValuePair>();
paramPairs.add(new BasicNameValuePair("username", "admin"));
paramPairs.add(new BasicNameValuePair("password", "123456"));
UrlEncodedFormEntity entity;
try {
// 4. 将参数设置到entity对象中
entity = new UrlEncodedFormEntity(paramPairs, "UTF-8");
// 5. 将entity对象设置到httppost对象中
httpPost.setEntity(entity);
System.out.println("executing POST request " + httpPost.getURI());
// 6. 发送请求并回去响应
CloseableHttpResponse resp = client.execute(httpPost);
try {
// 7. 获取响应entity
HttpEntity respEntity = resp.getEntity();
// 8. 打印出响应内容
if (null != respEntity) {
System.out.println("------");
System.out.println(resp.getStatusLine());
System.out.println("Response content is : \n" + EntityUtils.toString(respEntity, "UTF-8"));
System.out.println("------");
}
} finally {
// 9. 关闭响应对象
resp.close();
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
// 10. 关闭连接，释放资源
try {
client.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
HttpClientTest test = new HttpClientTest();
// 测试GET请求
test.get();
// 测试POST请求
test.post();
}
}
- 输出结果：
executing GET request http://localhost:8080/TomcatTest/hello
------
HTTP/1.1 200 OK
Response content length = 34
Response content is:
Hello world! 你好，世界！！
-----
executing POST request
http://localhost:8080/TomcatTest/hello
------
HTTP/1.1 200 OK
Response content is :
your username is:admin
your password is:123456
------
所需jar包下载
所需jar包打包下载地址：https://pan.baidu.com/s/1mhJ9iT6
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