Java调用http接口的几种方式（HttpURLConnection、OKHttp、HttpClient、RestTemplate）

Java调用HTTP接口可以使用以下几种方式：

1. HttpURLConnection：Java内置的轻量级HTTP客户端。
2. OKHttp：一个高效的HTTP客户端，支持连接池、缓存等机制。
3. HttpClient：Apache的HTTP客户端，功能丰富，但不是Android标准库的一部分。
4. RestTemplate：Spring框架中用于访问REST服务的客户端。

以下是每种方式的简单示例代码：

1. HttpURLConnection

URL url = new URL("http://example.com/api");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
 
int responseCode = conn.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
    BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    String inputLine;
    StringBuilder response = new StringBuilder();
    while ((inputLine = in.readLine()) != null) {
        response.append(inputLine);
    }
    in.close();
    // 处理response.toString()
}
conn.disconnect();

2. OKHttp

OkHttpClient client = new OkHttpClient();
 
Request request = new Request.Builder()
    .url("http://example.com/api")
    .get()
    .build();
 
Response response = client.newCall(request).execute();
if (response.isSuccessful()) {
    String responseBody = response.body().string();
    // 处理responseBody
}

3. HttpClient (需要Apache HttpClient库)

HttpClient client = HttpClientBuilder.create().build();
HttpGet request = new HttpGet("http://example.com/api");
 
HttpResponse response = client.execute(request);
if (response.getStatusLine().getStatusCode() == 200) {
    String responseBody = EntityUtils.toString(response.getEntity());
    // 处理responseBody
}

4. RestTemplate (Spring框架)

RestTemplate restTemplate = new RestTemplate();
String response = restTemplate.getForObject("http://example.com/api", String.class);
// 处理response