java 通信_使用JAVA实现http通信详解

Http通信概述

Http通信主要有两种方式POST方式和GET方式。前者通过Http消息实体发送数据给服务器，安全性高，数据传输大小没有限制，后者通过URL的查询字符串传递给服务器参数，以明文显示在浏览器地址栏，保密性差，最多传输2048个字符。但是GET请求并不是一无是处——GET请求大多用于查询(读取资源)，效率高。POST请求用于注册、登录等安全性较高且向数据库中写入数据的操作。

除了POST和GET，http通信还有其他方式！请参见http请求的方法

编码前的准备

在进行编码之前，我们先创建一个Servlet，该Servlet接收客户端的参数(name和age)，并响应客户端。

@WebServlet(urlPatterns={"/demo.do"})

public class DemoServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

request.setCharacterEncoding("utf-8");

response.setContentType("text/html;charset=utf-8");

String name = request.getParameter("name");

String age = request.getParameter("age");

PrintWriter pw = response.getWriter();

pw.print("您使用GET方式请求该Servlet。
" + "name = " + name + ",age = " + age);

pw.flush();

pw.close();

}

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

request.setCharacterEncoding("utf-8");

response.setContentType("text/html;charset=utf-8");

String name = request.getParameter("name");

String age = request.getParameter("age");

PrintWriter pw = response.getWriter();

pw.print("您使用POST方式请求该Servlet。
" + "name = " + name + ",age = " + age);

pw.flush();

pw.close();

}

}

使用JDK实现http通信

使用URLConnection实现GET请求

实例化一个java.net.URL对象；

通过URL对象的openConnection()方法得到一个java.net.URLConnection;

通过URLConnection对象的getInputStream()方法获得输入流；

读取输入流；

关闭资源。

public void get() throws Exception{

URL url = new URL("http://127.0.0.1/http/demo.do?name=Jack&age=10");

URLConnection urlConnection = url.openConnection(); // 打开连接

BufferedReader br = new BufferedReader(new InputStreamReader(urlConnection.getInputStream(),"utf-8")); // 获取输入流

String line = null;

StringBuilder sb = new StringBuilder();

while ((line = br.readLine()) != null) {

sb.append(line + "n");

}

System.out.println(sb.toString());

}

使用HttpURLConnection实现POST请求

java.net.HttpURLConnection是java.net.URL的子类，提供了更多的关于http的操作(getXXX 和 setXXX方法)。该类中定义了一系列的HTTP状态码：

public void post() throws IOException{

URL url = new URL("http://127.0.0.1/http/demo.do");

HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();

httpURLConnection.setDoInput(true);

httpURLConnection.setDoOutput(true); // 设置该连接是可以输出的

httpURLConnection.setRequestMethod("POST"); // 设置请求方式

httpURLConnection.setRequestProperty("charset", "utf-8");

PrintWriter pw = new PrintWriter(new BufferedOutputStream(httpURLConnection.getOutputStream()));

pw.write("name=welcome"); // 向连接中输出数据(相当于发送数据给服务器)

pw.write("&age=14");

pw.flush();

pw.close();

BufferedReader br = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream(),"utf-8"));

String line = null;

StringBuilder sb = new StringBuilder();

while ((line = br.readLine()) != null) { // 读取数据

sb.append(line + "n");

}

System.out.println(sb.toString());

}

使用httpclient进行http通信

httpclient大大简化了JDK中http通信的实现。

maven依赖：

org.apache.httpcomponents

httpclient

4.3.6

GET请求

public void httpclientGet() throws Exception{

// 创建HttpClient对象

HttpClient client = HttpClients.createDefault();

// 创建GET请求(在构造器中传入URL字符串即可)

HttpGet get = new HttpGet("http://127.0.0.1/http/demo.do?name=admin&age=40");

// 调用HttpClient对象的execute方法获得响应

HttpResponse response = client.execute(get);

// 调用HttpResponse对象的getEntity方法得到响应实体

HttpEntity httpEntity = response.getEntity();

// 使用EntityUtils工具类得到响应的字符串表示

String result = EntityUtils.toString(httpEntity,"utf-8");

System.out.println(result);

}

POST请求

public void httpclientPost() throws Exception{

// 创建HttpClient对象

HttpClient client = HttpClients.createDefault();

// 创建POST请求

HttpPost post = new HttpPost("http://127.0.0.1/http/demo.do");

// 创建一个List容器，用于存放基本键值对(基本键值对即：参数名-参数值)

List parameters = new ArrayList<>();

parameters.add(new BasicNameValuePair("name", "张三"));

parameters.add(new BasicNameValuePair("age", "25"));

// 向POST请求中添加消息实体

post.setEntity(new UrlEncodedFormEntity(parameters, "utf-8"));

// 得到响应并转化成字符串

HttpResponse response = client.execute(post);

HttpEntity httpEntity = response.getEntity();

String result = EntityUtils.toString(httpEntity,"utf-8");

System.out.println(result);

}

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。