Java调用第三方API接口：实现与实践

原创于 2025-08-22 11:18:10 发布 · 415 阅读

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在现代软件开发中，第三方API接口的使用已经变得极为普遍。无论是获取天气数据、用户身份验证，还是进行支付处理，API接口都为我们提供了强大的功能，极大地简化了开发流程。本文将详细介绍如何在Java中调用第三方API接口，包括准备工作、调用方法以及处理响应。

一、准备工作

在调用第三方API接口之前，我们需要做好以下准备工作：

注册并获取API密钥：大多数第三方API都需要一个API密钥（API Key）来进行身份验证。你需要在API提供方的官方网站上注册一个账号，然后创建一个应用以获取API密钥。
阅读API文档：了解API的请求方式（GET、POST等）、请求参数、返回数据格式等信息。这将帮助你正确地构建请求并处理响应。
选择合适的HTTP客户端库：Java中有多种HTTP客户端库可供选择，如HttpURLConnection、Apache HttpClient、OkHttp等。根据你的项目需求和个人喜好选择一个合适的库。

二、使用`HttpURLConnection`调用API

HttpURLConnection是Java自带的HTTP客户端库，虽然使用起来相对繁琐，但无需额外依赖。

示例：调用一个简单的GET请求

假设我们要调用一个天气API，获取某个城市的天气信息。

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

public class WeatherApiCaller {
    public static void main(String[] args) {
        String apiKey = "your_api_key";
        String city = "Beijing";
        String urlString = "http://api.weatherapi.com/v1/current.json?key=" + apiKey + "&q=" + city;

        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");

            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String inputLine;
                StringBuilder response = new StringBuilder();

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

                System.out.println("Response: " + response.toString());
            } else {
                System.out.println("GET request not worked");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

示例：发送POST请求

假设我们要调用一个用户登录API，需要发送POST请求。

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

public class LoginApiCaller {
    public static void main(String[] args) {
        String urlString = "http://example.com/api/login";
        String urlParameters = "username=your_username&password=your_password";

        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("POST");
            connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            connection.setRequestProperty("Content-Length", String.valueOf(urlParameters.getBytes().length));
            connection.setDoOutput(true);

            try (DataOutputStream wr = new DataOutputStream(connection.getOutputStream())) {
                wr.write(urlParameters.getBytes());
            }

            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String inputLine;
                StringBuilder response = new StringBuilder();

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

                System.out.println("Response: " + response.toString());
            } else {
                System.out.println("POST request not worked");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

三、使用`Apache HttpClient`调用API

Apache HttpClient是一个功能强大的HTTP客户端库，提供了更简洁的API和更多的功能。

示例：调用GET请求

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class WeatherApiCallerHttpClient {
    public static void main(String[] args) {
        String apiKey = "your_api_key";
        String city = "Beijing";
        String urlString = "http://api.weatherapi.com/v1/current.json?key=" + apiKey + "&q=" + city;

        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            HttpGet request = new HttpGet(urlString);
            HttpResponse response = httpClient.execute(request);

            HttpEntity entity = response.getEntity();
            if (entity != null) {
                String result = EntityUtils.toString(entity);
                System.out.println("Response: " + result);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

示例：发送POST请求

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class LoginApiCallerHttpClient {
    public static void main(String[] args) {
        String urlString = "http://example.com/api/login";
        String json = "{\"username\":\"your_username\",\"password\":\"your_password\"}";

        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            HttpPost request = new HttpPost(urlString);
            request.setHeader("Content-Type", "application/json");
            request.setEntity(new StringEntity(json));

            try (CloseableHttpResponse response = httpClient.execute(request)) {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    String result = EntityUtils.toString(entity);
                    System.out.println("Response: " + result);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

四、处理API响应

调用API后，我们需要处理返回的响应数据。通常，API返回的数据是JSON格式，我们可以使用Jackson或Gson等库来解析JSON数据。

示例：使用`Jackson`解析JSON响应

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

public class JsonParser {
    public static void main(String[] args) {
        String jsonResponse = "{\"location\":{\"name\":\"Beijing\",\"region\":\"Beijing\",\"country\":\"China\"},\"current\":{\"temp_c\":28.0,\"condition\":{\"text\":\"Sunny\",\"icon\":\"//cdn.weatherapi.com/weather/64x64/day/113.png\",\"code\":1000}}}";

        ObjectMapper objectMapper = new ObjectMapper();
        try {
            JsonNode rootNode = objectMapper.readTree(jsonResponse);
            JsonNode locationNode = rootNode.path("location");
            JsonNode currentNode = rootNode.path("current");

            String name = locationNode.path("name").asText();
            String region = locationNode.path("region").asText();
            String country = locationNode.path("country").asText();

            double tempC = currentNode.path("temp_c").asDouble();
            String conditionText = currentNode.path("condition").path("text").asText();

            System.out.println("Location: " + name + ", " + region + ", " + country);
            System.out.println("Temperature: " + tempC + "°C");
            System.out.println("Condition: " + conditionText);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

五、错误处理

在调用API时，可能会遇到各种错误，如网络问题、API限制、参数错误等。我们需要在代码中妥善处理这些错误。

示例：错误处理

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class ErrorHandlingApiCaller {
    public static void main(String[] args) {
        String apiKey = "your_api_key";
        String city = "Beijing";
        String urlString = "http://api.weatherapi.com/v1/current.json?key=" + apiKey + "&q=" + city;

        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            HttpGet request = new HttpGet(urlString);
            HttpResponse response = httpClient.execute(request);

            int statusCode = response.getStatusLine().getStatusCode();
            if (statusCode == 200) {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    String result = EntityUtils.toString(entity);
                    System.out.println("Response: " + result);
                }
            } else {
                System.out.println("Error: " + statusCode);
            }
        } catch (Exception e) {
            System.out.println("Exception: " + e.getMessage());
        }
    }
}