Java基礎教程——模擬瀏覽器發送請求

JAVA訪問網頁

分別測試使用get和post方法訪問網頁，可以收到服務器的請求，並寫入到html文件中。

import java.io.*;
import java.net.*;
import java.util.*;
public class TestGetPostPage {
	// param:請求參數，格式應該滿足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);
			// 打開和URL之間的連接
			HttpURLConnection conn = getHttpURLConnection(realUrl);
			// 打印頭信息
			printHeader(conn);
			// 獲取響應
			result = getResponse(conn);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return result;
	}
	// param:請求參數，格式應該滿足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);
			// 發送POST請求必須設置如下兩行
			conn.setDoOutput(true);
			conn.setDoInput(true);
			{// Post發送參數：
				// 獲取HttpURLConnection 對象對應的輸出流
				PrintWriter out = new PrintWriter(conn.getOutputStream());
				// 發送請求參數
				out.print(param);
				out.close();
			}
			// 獲取響應
			result = getResponse(conn);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return result;
	}
	// 提供主方法，測試發送GET請求和POST請求
	public static void main(String args[]) {
		String url = "http://www.shicimingju.com/book/xiyouji.html";
		// "https://zhuanlan.zhihu.com/hulaoshi";
		String param = null;
		// 也可以自己寫個Servlet測試是否接收到參數
		// url = "http://localhost:8080/TestJavaWeb/AHServlet";
		// param = "uname=tiger";
		// ----------------------------
		String s;
		// 發送GET請求
		s = TestGetPostPage.sendGet(url, param);
		write("http_get.html", s);
		System.out.println("-----------------------------------------------");
		// 發送POST請求
		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 {
			// 打開和URL之間的連接
			conn = (HttpURLConnection) realUrl.openConnection();
			// 設置通用的請求屬性
			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) {
		// 讀取URL的響應
		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 += "\n" + 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("---↓↓↓響應頭字段---");
		Map<String, List<String>> map = conn.getHeaderFields();
		for (String key : map.keySet()) {
			System.out.println(key + "--->" + map.get(key));
		}
		System.out.println("---↑↑↑響應頭字段---");
	}
	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();
		}
	}
}

還可以自己寫個Servlet測試服務器端是否接收到參數：

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多線程下載網絡文件

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

---

URLEncoder和URLDecoder

在使用百度搜索關鍵字的時候，往往會在地址欄看到如下內容：

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

有的瀏覽器直接看不到這段內容，地址欄中直接顯示輸入的關鍵字。這是因為瀏覽器對其進行了修飾，避免神秘代碼對用戶造成困擾，一般IE不會做這種修飾。

這里的“%E8%99%8E%E8%80%81%E7%8B%AE”就是你輸入的關鍵字，但是進行了編碼。

編碼，可以使用URLDecoder.decode(...)方法

解碼，可以使用URLEncoder.encode(...)方法

encoder：編碼器。
decoder：解碼器。

URL：Uniform Resource Locator，統一資源定位符。互聯網上的每個文件都有一個唯一的

URL。

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

效果在於轉換漢字等。

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

運行結果：

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