JAVA Post 和 GET请求

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

class Response {

    private final int code;
    private final byte[] data;

    Response(int code, byte[] data) {
        this.code = code;
        this.data = data;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(1024);
        sb.append(code).append("\n");
        String s = new String(data, StandardCharsets.UTF_8);
        if (s.length() > 1024) {
            sb.append(s.substring(0, 1024)).append("\n...");
        } else {
            sb.append(s);
        }
        return sb.toString();
    }
}

public class HttpClient {

    public static void main(String[] args) throws Exception {
        Response resp = get("https://www.douban.com");
        System.out.println(resp);

        Map<String, String> postMap = new HashMap<>();
        postMap.put("form_email", "test");
        postMap.put("form_password", "password");
        Response postResp = post("https://www.douban.com/accounts/login",
            "application/x-www-form-urlencoded",
            toFormData(postMap));
        System.out.println(postResp);
    }

    private static Response get(String theUrl) {
        System.err.println("GET: " + theUrl);
        HttpURLConnection conn = null;
        try {
            URL url = new URL(theUrl);
            conn = (HttpURLConnection) url.openConnection();
            ByteArrayOutputStream responseBuffer = new ByteArrayOutputStream();
            try (InputStream input = conn.getInputStream()) {
                byte[] buffer = new byte[1024];
                for (; ; ) {
                    int n = input.read(buffer);
                    if (n == (-1)) {
                        break;
                    }
                    responseBuffer.write(buffer, 0, n);
                }
            }
            return new Response(conn.getResponseCode(), responseBuffer.toByteArray());
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }
    }

    private static Response post(String theUrl, String contentType, String contentData) {
        System.err.println("POST: " + theUrl);
        HttpURLConnection conn = null;
        try {
            URL url = new URL(theUrl);
            conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);

            byte[] postData = contentData.getBytes(StandardCharsets.UTF_8);
            conn.setRequestProperty("Content-Type", contentType);
            conn.setRequestProperty("Content-Length", String.valueOf(postData.length));

            try (OutputStream output = conn.getOutputStream()) {
                output.write(postData);
            }
            ByteArrayOutputStream responseBuffer = new ByteArrayOutputStream();
            try (InputStream input = conn.getInputStream()) {
                byte[] buffer = new byte[1024];
                for (; ; ) {
                    int n = input.read(buffer);
                    if (n == (-1)) {
                        break;
                    }
                    responseBuffer.write(buffer, 0, n);
                }
            }
            return new Response(conn.getResponseCode(), responseBuffer.toByteArray());
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }
    }

    private static String toFormData(Map<String, String> map) throws IOException {
        List<String> list = new ArrayList<>(map.size());
        for (String key : map.keySet()) {
            list.add(key + "=" + URLEncoder.encode(map.get(key), "UTF-8"));
        }
        return String.join("&", list);
    }
}