java怎样截取网页字符串的指定部分内容？

给你一个java main的函数吧，没有用第三方jar包，只是通过java的Connection和正则实现的：

public static void main(String[] args) {
		StringBuffer res = new StringBuffer();
		HttpURLConnection conn = null;
		try {
			URL serverUrl = new URL("http://www.chapm25.com/city/beijing.html");
			conn = (HttpURLConnection) serverUrl.openConnection();
			conn.setRequestMethod("GET");// "POST" ,"GET"
			conn.setConnectTimeout(10000);
			conn.setReadTimeout(10000);
			conn.connect();
			InputStream ins = conn.getInputStream();
			String charset = "UTF-8";
			InputStreamReader inr = new InputStreamReader(ins, charset);
			BufferedReader bfr = new BufferedReader(inr);
			String line = "";
			do {
				res.append(line);
				line = bfr.readLine();
			} while (line != null);
			inr.close();
			bfr.close();
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			if (conn != null) {
				conn.disconnect();
			}
		}
		Pattern pattern = Pattern.compile("pmtips[\\w\\W].*?<h3>(.*?)</h3>");
		Matcher matcher = pattern.matcher(res);
		System.out.println(res);
		if (matcher.find()) {
			String ret = matcher.group(1);
			System.out.println(ret);
		}

	}

运行结果：

北京PM2.5为76