要从Java应用程序执行/触发Apache Nifi Processor，您可以使用Nifi的REST API。以下是一个简单的代码示例，演示如何使用Java发送REST请求来执行Nifi Processor。

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;

import java.io.IOException;

public class ExecuteNifiProcessor {

    public static void main(String[] args) {
        // 设置Nifi的主机和端口
        String nifiHost = "localhost";
        int nifiPort = 8080;

        // 设置要执行的Processor的ID
        String processorId = "your_processor_id";

        // 创建HTTP客户端
        CloseableHttpClient httpClient = HttpClients.createDefault();

        // 构建执行Processor的请求URL
        String requestUrl = String.format("http://%s:%d/nifi-api/processors/%s/run-status", nifiHost, nifiPort, processorId);

        // 创建HTTP POST请求
        HttpPost httpPost = new HttpPost(requestUrl);

        // 设置请求头
        httpPost.addHeader("Content-Type", "application/json");

        try {
            // 执行请求
            CloseableHttpResponse response = httpClient.execute(httpPost);
            HttpEntity entity = response.getEntity();

            // 处理响应
            if (entity != null) {
                String responseString = EntityUtils.toString(entity);
                System.out.println(responseString);
            }

            // 关闭响应和HTTP客户端
            response.close();
            httpClient.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

上述代码将向指定的Nifi实例的指定Processor发送一个POST请求，以执行该Processor。您需要更改nifiHost，nifiPort和processorId变量以匹配您的设置。请确保您已在项目的构建路径中包含所需的依赖项，例如Apache HttpClient。

请注意，此代码示例仅仅展示了如何通过Java应用程序触发Nifi Processor，实际情况可能更复杂，具体取决于您的要求和设置。