我应该使用 HttpURLConnection 还是 RestTemplate [重复]

Question

我应该在Spring 项目中使用HttpURLConnection 还是更好地使用RestTemplate？ 换句话说，什么时候使用每个更好？

Answer 1

HttpURLConnection 和RestTemplate 是不同种类的野兽。它们在不同的抽象级别上运行。

RestTemplate 有助于使用 REST api，HttpURLConnection 与 HTTP 协议一起使用。

您在问什么更好用。答案取决于您要达到的目标：

• 如果您需要使用REST api，请坚持使用RestTemplate
• 如果您需要使用 http 协议，请使用 HttpURLConnection、OkHttpClient、Apache 的 HttpClient，或者如果您使用 Java 11，则可以尝试其 HttpClient。

此外，RestTemplate 使用 HttpUrlConnection/OkHttpClient/... 来完成其工作（请参阅 ClientHttpRequestFactory、SimpleClientHttpRequestFactory、OkHttp3ClientHttpRequestFactory

---

为什么不应该使用HttpURLConnection？

最好显示一些代码：

在下面的示例中使用JSONPlaceholder

让我们GET一个帖子：

public static void main(String[] args) {
  URL url;
  try {
    url = new URL("https://jsonplaceholder.typicode.com/posts/1");
  } catch (MalformedURLException e) {
    // Deal with it.
    throw new RuntimeException(e);
  }
  HttpURLConnection connection = null;
  try {
    connection = (HttpURLConnection) url.openConnection();
    try (InputStream inputStream = connection.getInputStream();
         InputStreamReader isr = new InputStreamReader(inputStream);
         BufferedReader bufferedReader = new BufferedReader(isr)) {
      // Wrap, wrap, wrap

      StringBuilder response = new StringBuilder();
      String line;
      while ((line = bufferedReader.readLine()) != null) {
        response.append(line);
      }
      // Here is the response body
      System.out.println(response.toString());
    }

  } catch (IOException e) {
    throw new RuntimeException(e);
  } finally {
    if (connection != null) {
      connection.disconnect();
    }
  }
}

现在让我们POST 发布一些东西：

connection = (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.setDoOutput(true);
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-type", "application/json; charset=UTF-8");

try (OutputStream os = connection.getOutputStream();
     OutputStreamWriter osw = new OutputStreamWriter(os);
     BufferedWriter wr = new BufferedWriter(osw)) {
  wr.write("{\"title\":\"foo\", \"body\": \"bar\", \"userId\": 1}");
}

如果需要响应：

try (InputStream inputStream = connection.getInputStream();
     InputStreamReader isr = new InputStreamReader(inputStream);
     BufferedReader bufferedReader = new BufferedReader(isr)) {
  // Wrap, wrap, wrap

  StringBuilder response = new StringBuilder();
  String line;
  while ((line = bufferedReader.readLine()) != null) {
    response.append(line);
  }

  System.out.println(response.toString());
}

如您所见，HttpURLConnection 提供的 api 是苦行僧。

你总是要处理“低级”InputStream、Reader、OutputStream、Writer，但幸运的是还有其他选择。

---

OkHttpClient

OkHttpClient 减轻痛苦：

GET发帖：

OkHttpClient okHttpClient = new OkHttpClient();
Request request = new Request.Builder()
    .url("https://jsonplaceholder.typicode.com/posts/1")
    .build();
Call call = okHttpClient.newCall(request);
try (Response response = call.execute();
     ResponseBody body = response.body()) {

  String string = body.string();
  System.out.println(string);
} catch (IOException e) {
  throw new RuntimeException(e);
}

POST发帖：

Request request = new Request.Builder()
    .post(RequestBody.create(MediaType.parse("application/json; charset=UTF-8"),
        "{\"title\":\"foo\", \"body\": \"bar\", \"userId\": 1}"))
    .url("https://jsonplaceholder.typicode.com/posts")
    .build();

Call call = okHttpClient.newCall(request);

try (Response response = call.execute();
     ResponseBody body = response.body()) {

  String string = body.string();
  System.out.println(string);
} catch (IOException e) {
  throw new RuntimeException(e);
}

容易多了，对吧？

Java 11 的 HttpClient

GETting 发帖：

HttpClient httpClient = HttpClient.newHttpClient();

HttpResponse<String> response = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://jsonplaceholder.typicode.com/posts/1"))
    .GET()
    .build(), HttpResponse.BodyHandlers.ofString());

System.out.println(response.body());

POST发帖：

HttpResponse<String> response = httpClient.send(HttpRequest.newBuilder()
    .header("Content-Type", "application/json; charset=UTF-8")
    .uri(URI.create("https://jsonplaceholder.typicode.com/posts"))
    .POST(HttpRequest.BodyPublishers.ofString("{\"title\":\"foo\", \"body\": \"barzz\", \"userId\": 2}"))
    .build(), HttpResponse.BodyHandlers.ofString());

---

RestTemplate

根据它的javadoc：

用于执行 HTTP 请求的同步客户端，通过底层 HTTP 客户端库（例如 JDK {@code HttpURLConnection}、Apache HttpComponents 等）公开一个简单的模板方法 API。

让我们做同样的事情

首先为方便起见，创建了Post 类。 （当RestTemplate 读取响应时，它将使用HttpMessageConverter 将其转换为Post）

public static class Post {
  public long userId;
  public long id;
  public String title;
  public String body;

  @Override
  public String toString() {
    return new ReflectionToStringBuilder(this)
        .toString();
  }
}

GET发帖。

RestTemplate restTemplate = new RestTemplate();
ResponseEntity<Post> entity = restTemplate.getForEntity("https://jsonplaceholder.typicode.com/posts/1", Post.class);
Post post = entity.getBody();
System.out.println(post);

POST发帖：

public static class PostRequest {
  public String body;
  public String title;
  public long userId;
}

public static class CreatedPost {
  public String body;
  public String title;
  public long userId;
  public long id;

  @Override
  public String toString() {
    return new ReflectionToStringBuilder(this)
        .toString();
  }
}

public static void main(String[] args) {

  PostRequest postRequest = new PostRequest();
  postRequest.body = "bar";
  postRequest.title = "foo";
  postRequest.userId = 11;


  RestTemplate restTemplate = new RestTemplate();
  CreatedPost createdPost = restTemplate.postForObject("https://jsonplaceholder.typicode.com/posts/", postRequest, CreatedPost.class);
  System.out.println(createdPost);
}

---

所以回答你的问题：

什么时候使用每个更好？

• 需要消耗REST api？使用RestTemplate
• 需要使用 http 吗？使用一些HttpClient。

---

还值得一提：

• Retrofit
• Intro to Feign
• Declarative REST client