Java基础教程——模拟浏览器发送请求

JAVA访问网页

分别测试使用get和post方法访问网页，可以收到服务器的请求，并写入到html文件中。

import java.io.*;
import java.net.*;
import java.util.*;
public class TestGetPostPage {
	// param:请求参数，格式应该满足name1=value1&name2=value2的形式。
	public static String sendGet(String url, String param) {
		String result = "";
		if (param != null) {
			url = url + "?" + param;
		}
		try {
			URL realUrl = new URL(url);
			// 打开和URL之间的连接
			HttpURLConnection conn = getHttpURLConnection(realUrl);
			// 打印头信息
			printHeader(conn);
			// 获取响应
			result = getResponse(conn);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return result;
	}
	// param:请求参数，格式应该满足name1=value1&name2=value2的形式。
	public static String sendPost(String url, String param) {
		String result = "";
		try {
			URL realUrl = new URL(url);
			HttpURLConnection conn = getHttpURLConnection(realUrl);
			// 发送POST请求必须设置如下两行
			conn.setDoOutput(true);
			conn.setDoInput(true);
			{// Post发送参数：
				// 获取HttpURLConnection 对象对应的输出流
				PrintWriter out = new PrintWriter(conn.getOutputStream());
				// 发送请求参数
				out.print(param);
				out.close();
			}
			// 获取响应
			result = getResponse(conn);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return result;
	}
	// 提供主方法，测试发送GET请求和POST请求
	public static void main(String args[]) {
		String url = "http://www.shicimingju.com/book/xiyouji.html";
		// "https://zhuanlan.zhihu.com/hulaoshi";
		String param = null;
		// 也可以自己写个Servlet测试是否接收到参数
		// url = "http://localhost:8080/TestJavaWeb/AHServlet";
		// param = "uname=tiger";
		// ----------------------------
		String s;
		// 发送GET请求
		s = TestGetPostPage.sendGet(url, param);
		write("http_get.html", s);
		System.out.println("-----------------------------------------------");
		// 发送POST请求
		s = TestGetPostPage.sendPost(url, param);
		write("http_post.html", s);
	}
	private static HttpURLConnection getHttpURLConnection(URL realUrl) {
		StringBuilder sb = new StringBuilder();
		sb.append("Mozilla/5.0 (Windows NT 10.0; Win64; x64)");
		sb.append(" AppleWrbKit/537.36(KHTML, like Gecko)");
		sb.append(" Chrome/72.0.3626.119 Safari/537.36");
		HttpURLConnection conn = null;
		try {
			// 打开和URL之间的连接
			conn = (HttpURLConnection) realUrl.openConnection();
			// 设置通用的请求属性
			conn.setRequestProperty("accept", "*/*");
			conn.setRequestProperty("connection", "Keep-Alive");
			conn.setRequestProperty("user-agent", sb.toString());
		} catch (IOException e) {
			e.printStackTrace();
		}
		return conn;
	}
	private static String getResponse(HttpURLConnection conn) {
		// 读取URL的响应
		String result = "";
		try (InputStream is = conn.getInputStream();
				InputStreamReader isr = new InputStreamReader(is, "utf-8");
				BufferedReader in = new BufferedReader(isr)) {
			String line;
			while ((line = in.readLine()) != null) {
				result += "
" + line;
			}
		} catch (Exception e) {
			System.out.println("Err:getResponse()");
			e.printStackTrace();
		} finally {
			conn.disconnect();
		}
		System.out.println("getResponse()：" + result.length());
		return result;
	}
	private static void printHeader(HttpURLConnection conn) {
		System.out.println("---↓↓↓响应头字段---");
		Map<String, List<String>> map = conn.getHeaderFields();
		for (String key : map.keySet()) {
			System.out.println(key + "--->" + map.get(key));
		}
		System.out.println("---↑↑↑响应头字段---");
	}
	private static void write(String fileName, String text) {
		File f = new File(fileName);
		try (FileOutputStream fos = new FileOutputStream(f);
				OutputStreamWriter osw = new OutputStreamWriter(fos, "UTF-8");
				BufferedWriter bw = new BufferedWriter(osw);) {
			bw.write(text);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

还可以自己写个Servlet测试服务器端是否接收到参数：

import java.io.*;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
@WebServlet("/AHServlet")
public class AHServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String parameter = request.getParameter("uname");
		System.out.println("Get : " + parameter);
		resp(response);
	}
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String parameter = request.getParameter("uname");
		System.out.println("Post : " + parameter);
		resp(response);
	}
	private void resp(HttpServletResponse response) throws IOException {
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.println("https://www.bilibili.com/video/av48272174/?p=2");
		out.flush();
		out.close();
	}
}

*JAVA多线程下载网络文件

[参见]: https://www.cnblogs.com/tigerlion/p/10661367.html

---

URLEncoder和URLDecoder

在使用百度搜索关键字的时候，往往会在地址栏看到如下内容：

https://www.baidu.com/s?ie=utf-8&f=8&rsv_bp=1&rsv_idx=2&tn=baiduhome_pg&wd=%E8%99%8E%E8%80%81%E7%8B%AE

有的浏览器直接看不到这段内容，地址栏中直接显示输入的关键字。这是因为浏览器对其进行了修饰，避免神秘代码对用户造成困扰，一般IE不会做这种修饰。

这里的“%E8%99%8E%E8%80%81%E7%8B%AE”就是你输入的关键字，但是进行了编码。

编码，可以使用URLDecoder.decode(...)方法

解码，可以使用URLEncoder.encode(...)方法

encoder：编码器。
decoder：解码器。

URL：Uniform Resource Locator，统一资源定位符。互联网上的每个文件都有一个唯一的

URL。

普通字符串 ←→ application/x-www-form-rulencoded MIME字符串

效果在于转换汉字等。

import java.net.*;
public class _12URLDecoderTest {
	public static void main(String[] args) throws Exception {
		// 将application/x-www-form-urlencoded字符串
		// 转换成普通字符串
		String keyWord = URLDecoder.decode("%E8%99%8E%E8%80%81%E7%8B%AE", "UTF-8");
		System.out.println(keyWord);
		// 将普通字符串转换成
		// application/x-www-form-urlencoded字符串
		String urlStr = URLEncoder.encode("无字真经", "GBK");
		System.out.println(urlStr);
		urlStr = URLEncoder.encode("无字真经", "UTF-8");
		System.out.println(urlStr);
	}
}

运行结果：

虎老狮
%CE%DE%D7%D6%D5%E6%BE%AD
%E6%97%A0%E5%AD%97%E7%9C%9F%E7%BB%8F