如何从GAE java代码而不是Maven运行Dataflow pipline？

从GAE Java代码而不是Maven运行Dataflow pipeline的方法是通过使用Google Cloud Dataflow SDK for Java。以下是详细步骤：

首先，确保已经安装了Java开发环境和Google Cloud SDK。
在GAE Java项目中，添加Dataflow SDK for Java的依赖项。可以在项目的pom.xml文件中添加以下依赖项：

<dependency>
  <groupId>com.google.cloud.dataflow</groupId>
  <artifactId>google-cloud-dataflow-java-sdk-all</artifactId>
  <version>2.5.0</version>
</dependency>

创建一个Dataflow pipline的Java类，并实现所需的转换逻辑。例如，可以创建一个类来计算Pi的近似值：

import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.TextIO;
import org.apache.beam.sdk.options.PipelineOptions;
import org.apache.beam.sdk.options.PipelineOptionsFactory;
import org.apache.beam.sdk.transforms.Count;
import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.sdk.transforms.ParDo;

public class DataflowPipeline {
  public static void main(String[] args) {
    PipelineOptions options = PipelineOptionsFactory.create();
    Pipeline pipeline = Pipeline.create(options);

    pipeline
      .apply(TextIO.read().from("gs://bucket/input.txt"))
      .apply(ParDo.of(new CountWords()))
      .apply(Count.perElement())
      .apply(ParDo.of(new FormatResult()))
      .apply(TextIO.write().to("gs://bucket/output.txt"));

    pipeline.run();
  }

  public static class CountWords extends DoFn<String, String> {
    @ProcessElement
    public void processElement(ProcessContext c) {
      String[] words = c.element().split(" ");
      for (String word : words) {
        c.output(word);
      }
    }
  }

  public static class FormatResult extends DoFn<KV<String, Long>, String> {
    @ProcessElement
    public void processElement(ProcessContext c) {
      String result = c.element().getKey() + ": " + c.element().getValue();
      c.output(result);
    }
  }
}

在GAE Java项目中，创建一个Servlet或其他入口点来启动Dataflow pipline。例如，可以创建一个Servlet类来触发Dataflow pipline的运行：

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.beam.sdk.PipelineResult;

@WebServlet("/rundataflow")
public class RunDataflowServlet extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
    PipelineResult result = DataflowPipeline.main(new String[]{});
    // 处理Dataflow pipline的结果
  }
}