简述

本文学习如何简单的使用POST，如何上传文件等等场景

基础POST

首先，让我们来看一个简单的例子，并使用HttpClient发送POST请求。

我们将使用两个参数 - “username”和“password” 进行POST ：

@Test
public void test() 
  throws ClientProtocolException, IOException {
    CloseableHttpClient client = HttpClients.createDefault();

    List<NameValuePair> params = new ArrayList<NameValuePair>();
    params.add(new BasicNameValuePair("username", "John"));
    params.add(new BasicNameValuePair("password", "pass"));
    httpPost.setEntity(new UrlEncodedFormEntity(params));
 
    HttpPost httpPost = new HttpPost("http://localhost:8080");

    CloseableHttpResponse response = client.execute(httpPost);
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

请注意我们如何使用List<NameValuePair>在POST请求中包含参数。

使用授权进行POST

接下来，让我们看看如何使用HttpClient对身份验证凭据进行POST 。

在以下示例中 - 我们通过添加Authorization在Header向使用基本身份验证保护的URL发送POST请求：

@Test
public void test()
  throws ClientProtocolException, IOException, AuthenticationException {
    CloseableHttpClient client = HttpClients.createDefault();

    HttpPost httpPost = new HttpPost("http://localhost:8080");


   httpPost.setEntity(new StringEntity("test post"));
    UsernamePasswordCredentials creds
      = new UsernamePasswordCredentials("John", "pass");
    httpPost.addHeader(new BasicScheme().authenticate(creds, httpPost, null));
 
    CloseableHttpResponse response = client.execute(httpPost);
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

使用JSON POST

现在 - 让我们看看如何使用HttpClient向JSON主体发送POST请求。

在以下示例中 - 我们将一些Person（id，name）作为JSON发送：

@Test
public void test() 
  throws ClientProtocolException, IOException {
    CloseableHttpClient client = HttpClients.createDefault();

    HttpPost httpPost = new HttpPost("http://localhost:8080");

    String json = "{"id":1,"name":"John"}";
    StringEntity entity = new StringEntity(json);
    httpPost.setEntity(entity);
    httpPost.setHeader("Accept", "application/json");
    httpPost.setHeader("Content-type", "application/json");
 
    CloseableHttpResponse response = client.execute(httpPost);
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

注意我们如何使用StringEntity来设置请求的主体。

我们还将ContentType标头设置为application / json ，以便为服务器提供有关我们发送的内容表示的必要信息。

使用HttpClient Form进行 POST

接下来，让我们使用HttpClient Fluent API进行POST 。

我们将发送一个带有两个参数“ username ”和“ password ” 的请求：

@Test
public void test() 
  throws ClientProtocolException, IOException {
    HttpResponse response = Request.Post("http://localhost:8080").bodyForm(
      Form.form().add("username", "John").add("password", "pass").build())
      .execute().returnResponse();
 
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
}

POST多参数请求

现在，让我们发一个多参数请求。

我们将使用MultipartEntityBuilder发布文件，useranme和password：

@Test
public void whenSendMultipartRequestUsingHttpClient_thenCorrect() 
  throws ClientProtocolException, IOException {
    CloseableHttpClient client = HttpClients.createDefault();

    HttpPost httpPost = new HttpPost("http://localhost:8080");

    MultipartEntityBuilder builder = MultipartEntityBuilder.create();
    builder.addTextBody("username", "John");
    builder.addTextBody("password", "pass");
    builder.addBinaryBody("file", new File("test.txt"), ContentType.APPLICATION_OCTET_STREAM, "file.ext");
 
    HttpEntity multipart = builder.build();
    httpPost.setEntity(multipart);
 
    CloseableHttpResponse response = client.execute(httpPost);
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

使用HttpClient上传文件

接下来，让我们看看如何使用HttpClient上传文件。

我们将使用MultipartEntityBuilder上传“ test.txt ”文件：

@Test
public void test() throws ClientProtocolException, IOException {
    CloseableHttpClient client = HttpClients.createDefault();

    HttpPost httpPost = new HttpPost("http://localhost:8080");

    MultipartEntityBuilder builder = MultipartEntityBuilder.create();
    builder.addBinaryBody("file", new File("test.txt"), ContentType.APPLICATION_OCTET_STREAM, "file.ext");
    HttpEntity multipart = builder.build();
    httpPost.setEntity(multipart);
 
    CloseableHttpResponse response = client.execute(httpPost);
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

获取文件上传 进度

最后 - 让我们看看如何使用HttpClient获取文件上传的进度。

在下面的示例中，我们将扩展HttpEntityWrapper以获得对上载过程的可见性。

首先 - 这是上传方法：

@Test
public void test()
  throws ClientProtocolException, IOException {
    CloseableHttpClient client = HttpClients.createDefault();

    HttpPost httpPost = new HttpPost("http://localhost:8080");

    MultipartEntityBuilder builder = MultipartEntityBuilder.create();
    builder.addBinaryBody("file", new File("test.txt"), ContentType.APPLICATION_OCTET_STREAM, "file.ext");
    HttpEntity multipart = builder.build();
 
    ProgressEntityWrapper.ProgressListener pListener = 
      percentage -> assertFalse(Float.compare(percentage, 100) > 0);
    httpPost.setEntity(new ProgressEntityWrapper(multipart, pListener));
 
    CloseableHttpResponse response = client.execute(httpPost);
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

我们还将添加接口ProgressListener，使我们能够观察上传进度：

public static interface ProgressListener {
    void progress(float percentage);
}

这是我们的扩展版HttpEntityWrapper的ProgressEntityWrapper：

public class ProgressEntityWrapper extends HttpEntityWrapper {
    private ProgressListener listener;
 
    public ProgressEntityWrapper(HttpEntity entity, ProgressListener listener) {
        super(entity);
        this.listener = listener;
    }
 
    @Override
    public void writeTo(OutputStream outstream) throws IOException {
        super.writeTo(new CountingOutputStream(outstream, listener, getContentLength()));
    }
}

而FilterOutputStream的扩展版CountingOutputStream：

public static class CountingOutputStream extends FilterOutputStream {
    private ProgressListener listener;
    private long transferred;
    private long totalBytes;
 
    public CountingOutputStream(
      OutputStream out, ProgressListener listener, long totalBytes) {
        super(out);
        this.listener = listener;
        transferred = 0;
        this.totalBytes = totalBytes;
    }
 
    @Override
    public void write(byte[] b, int off, int len) throws IOException {
        out.write(b, off, len);
        transferred += len;
        listener.progress(getCurrentProgress());
    }
 
    @Override
    public void write(int b) throws IOException {
        out.write(b);
        transferred++;
        listener.progress(getCurrentProgress());
    }
 
    private float getCurrentProgress() {
        return ((float) transferred / totalBytes) * 100;
    }
}

注意：

• 将FilterOutputStream扩展为CountingOutputStream时 -我们重写write（）方法来计算写入（传输）的字节数
• 将HttpEntityWrapper扩展为ProgressEntityWrapper时 -我们重写writeTo（）方法以使用我们的CountingOutputStream

小结

HttpClient的基础知识到本文就已经介绍结束，希望对你有所收获。