在Java中使用HttpClient提交表單可以通過以下步驟實現：

1. 添加依賴：首先，需要在項目中添加HttpClient的依賴。可以使用Maven或者Gradle來管理依賴。

Maven依賴：

<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<version>4.5.13</version>
</dependency>

Gradle依賴：

implementation 'org.apache.httpcomponents:httpclient:4.5.13'

2. 創建HttpClient對象：使用HttpClientBuilder來創建一個HttpClient對象。

HttpClient httpClient = HttpClientBuilder.create().build();

3. 創建HttpPost請求：使用HttpPost來創建一個HTTP POST請求，并設置表單數據。

HttpPost httpPost = new HttpPost(url);
List<NameValuePair> formParams = new ArrayList<>();
formParams.add(new BasicNameValuePair("param1", "value1"));
formParams.add(new BasicNameValuePair("param2", "value2"));
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formParams, "UTF-8");
httpPost.setEntity(entity);

4. 發送請求并獲取響應：使用HttpClient的execute方法發送請求，并獲取響應。

HttpResponse response = httpClient.execute(httpPost);

5. 解析響應：根據需要對響應進行解析和處理。

int statusCode = response.getStatusLine().getStatusCode();
HttpEntity responseEntity = response.getEntity();
if (statusCode == HttpStatus.SC_OK && responseEntity != null) {
String responseBody = EntityUtils.toString(responseEntity);
// 對響應進行處理
} else {
// 處理請求失敗的情況
}

完整的示例代碼如下：

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class HttpClientExample {
public static void main(String[] args) {
// 創建HttpClient對象
HttpClient httpClient = HttpClientBuilder.create().build();
// 創建HttpPost請求
String url = "http://example.com/submit";
HttpPost httpPost = new HttpPost(url);
// 設置表單數據
List<NameValuePair> formParams = new ArrayList<>();
formParams.add(new BasicNameValuePair("param1", "value1"));
formParams.add(new BasicNameValuePair("param2", "value2"));
try {
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formParams, "UTF-8");
httpPost.setEntity(entity);
// 發送請求并獲取響應
HttpResponse response = httpClient.execute(httpPost);
// 解析響應
int statusCode = response.getStatusLine().getStatusCode();
HttpEntity responseEntity = response.getEntity();
if (statusCode == HttpStatus.SC_OK && responseEntity != null) {
String responseBody = EntityUtils.toString(responseEntity);
// 對響應進行處理
} else {
// 處理請求失敗的情況
}
} catch (IOException e) {
e.printStackTrace();
}
}
}

注意：以上示例代碼僅為演示提交表單的基本步驟，實際項目中可能需要根據具體需求進行適當的修改和擴展。