《Java核心技术 卷II》获取Web数据提交表单数据

提交表单数据

了解即可，直接上案例

package 第4章网络.post;

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.Reader;
import java.net.CookieHandler;
import java.net.CookieManager;
import java.net.CookiePolicy;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Map;
import java.util.Properties;
import java.util.Scanner;

public class PostTest {

    public static void main(String[] args) throws IOException {
        String propsFilename = args.length > 0 ? args[0]
                : "D:\\ChromeCoreDownloads\\eclipse-jee-2024-09-R-win32-x86_64\\eclipse\\eclipse-workspace\\JavaCore2/src/第4章网络/post/post.properties";
        var props = new Properties();
        try (Reader in = Files.newBufferedReader(Path.of(propsFilename), StandardCharsets.UTF_8)) {
            props.load(in);
        }
        String urlString = props.remove("url").toString();
        Object userAgent = props.remove("User-Agent");
        Object redirects = props.remove("redirects");
        CookieHandler.setDefault(new CookieManager(null, CookiePolicy.ACCEPT_ALL));
        String result = doPost(new URL(urlString), props, userAgent == null ? null : userAgent.toString(),
                redirects == null ? -1 : Integer.parseInt(redirects.toString()));
        System.out.println(result);
    }

    public static String doPost(URL url, Map<Object, Object> nameValuePairs, String userAgent, int redirects)
            throws IOException {
        var connection = (HttpURLConnection) url.openConnection();
        if (userAgent != null)
            connection.setRequestProperty("User-Agent", userAgent);
        if (redirects > 0)
            connection.setInstanceFollowRedirects(false);
        connection.setDoOutput(true);
        try (var out = new PrintWriter(connection.getOutputStream())) {
            boolean first = true;
            for (Map.Entry<Object, Object> pair : nameValuePairs.entrySet()) {
                if (first)
                    first = false;
                else
                    out.print('&');
                String name = pair.getKey().toString();
                String value = pair.getValue().toString();
                out.print(name);
                out.print("=");
                out.print(URLEncoder.encode(value, StandardCharsets.UTF_8));
            }
        }
        String encoding = connection.getContentEncoding();
        if (encoding == null)
            encoding = "UTF-8";
        if (redirects > 0) {
            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_MOVED_TEMP || responseCode == HttpURLConnection.HTTP_MOVED_PERM
                    || responseCode == HttpURLConnection.HTTP_SEE_OTHER) {
                String location = connection.getHeaderField("Location");
                if (location != null) {
                    URL base = connection.getURL();
                    connection.disconnect();
                    return doPost(new URL(base, location), nameValuePairs, userAgent, redirects - 1);
                }
            }
        } else if (redirects == 0) {
            throw new IOException("太多次重定向");
        }
        var response = new StringBuilder();
        try (var in = new Scanner(connection.getInputStream(), encoding)) {
            while (in.hasNextLine()) {
                response.append(in.nextLine());
                response.append("\n");
            }
        } catch (IOException e) {
            InputStream err = connection.getErrorStream();
            if (err == null)
                throw e;
            try (var in = new Scanner(err)) {
                response.append(in.nextLine());
                response.append("\n");
            }
        }
        return response.toString();
    }

}