java 请求url拼接多个参数

在Java中，请求URL拼接多个参数通常使用`HttpURLConnection`、`HttpClient`或者其他HTTP客户端库。这里我将演示如何使用最基础的`HttpURLConnection`来构建一个包含多个参数的GET请求URL：

import java.net.URL;
import java.net.HttpURLConnection;

public class URLBuilder {
    private static final String PARAM_SEPARATOR = "&"; // 参数分隔符

    public static void main(String[] args) {
        String baseUrl = "http://example.com/api";
        String key1 = "value1";
        String key2 = "value2";
        String key3 = "value3";

        // 构造查询字符串
        String queryParameters = key1 + "=" + urlEncode(key1) + PARAM_SEPARATOR +
                                 key2 + "=" + urlEncode(key2) + PARAM_SEPARATOR +
                                 key3 + "=" + urlEncode(key3);

        // 构建完整的URL
        URL url = new URL(baseUrl + "?" + queryParameters);

        try (HttpURLConnection connection = (HttpURLConnection) url.openConnection()) {
            // 设置请求方法（这里是GET）
            connection.setRequestMethod("GET");

            // 打开连接并获取响应
            int responseCode = connection.getResponseCode();
            System.out.println("Response Code : " + responseCode);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 将字符串转换为URL编码，避免特殊字符导致的问题
    private static String urlEncode(String str) {
        try {
            return URLEncoder.encode(str, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e); // 程序中不应出现这种情况，但这里为了示例完整性
        }
    }
}