java使用webservice 调用天气预报接口

市场上有许多免费的和付费的天气预报API，例如OpenWeatherMap、WeatherAPI、Weatherstack等。这里我们以OpenWeatherMap为例，因为它提供了广泛的天气数据和相对简单的API接口。

访问OpenWeatherMap的官网（https://openweathermap.org/） ，注册一个账户，并创建一个API密钥（APIkey）。这个密钥将用于你的请求中，以验证身份和访问权限。

可以使用java.net.HttpURLConnection，或者Apache HttpClient、OkHttp等来调用接口。

1.使用java.net.HttpURLConnection来调用OpenWeatherMap API获取天气预报的：

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

public class WeatherClient {

    public static void main(String[] args) {
        try {
            String apiKey = "你的API密钥";
            String cityName = "Beijing";
            String urlString = "http://api.openweathermap.org/data/2.5/weather?q=" + cityName + "&appid=" + apiKey + "&units=metric";

            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            connection.setRequestMethod("GET");
            connection.setRequestProperty("Accept", "application/json");

            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                throw new RuntimeException("Failed : HTTP error code : " + connection.getResponseCode());
            }

            BufferedReader br = new BufferedReader(new InputStreamReader((connection.getInputStream())));

            String output;
            System.out.println("Output from Server .... \n");
            while ((output = br.readLine()) != null) {
                System.out.println(output);
            }

            connection.disconnect();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2.使用OkHttp库示例：

OkHttpClient client = new OkHttpClient();

String url = "http://api.openweathermap.org/data/2.5/weather?q=" + cityName + "&appid=" + apiKey + "&units=metric";

Request request = new Request.Builder()
    .url(url)
    .build();

try (Response response = client.newCall(request).execute()) {
    if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

    System.out.println(response.body().string());
} catch (IOException e) {
    e.printStackTrace();
}