在Java中調用REST接口通常使用HttpURLConnection或HttpClient來發送HTTP請求并接收響應。以下是一個簡單的示例代碼：

使用HttpURLConnection：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class RestClient {

    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com/api/resource");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Content-Type", "application/json");

            BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String inputLine;
            StringBuffer response = new StringBuffer();

            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();

            System.out.println(response.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

使用HttpClient：

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.util.EntityUtils;

public class RestClient {

    public static void main(String[] args) {
        HttpClient httpClient = HttpClientBuilder.create().build();
        HttpGet request = new HttpGet("http://example.com/api/resource");
        request.addHeader("Content-Type", "application/json");

        try {
            HttpResponse response = httpClient.execute(request);
            String responseBody = EntityUtils.toString(response.getEntity());
            System.out.println(responseBody);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

上述代碼示例使用GET方法調用REST接口，并輸出響應內容。根據實際情況，您可能需要修改HTTP方法、請求頭或請求體等參數。