Google数据流中的单例

public class GlobalConfig {
    private static GlobalConfig instance;
    private String configValue;

    private GlobalConfig() {}

    public static synchronized GlobalConfig getInstance() {
        if (instance == null) {
            instance = new GlobalConfig();
        }
        return instance;
    }

    public String getConfigValue() {
        return configValue;
    }

    public void setConfigValue(String configValue) {
        this.configValue = configValue;
    }
}

public class SharedResource {
    private static SharedResource instance;
    private Connection dbConnection;

    private SharedResource() {
        // 初始化数据库连接
        dbConnection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "user", "password");
    }

    public static synchronized SharedResource getInstance() {
        if (instance == null) {
            instance = new SharedResource();
        }
        return instance;
    }

    public Connection getDbConnection() {
        return dbConnection;
    }
}

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

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

        pipeline.apply(ParDo.of(new DoFn<String, String>() {
            @ProcessElement
            public void processElement(@Element String input, OutputReceiver<String> out) {
                GlobalConfig config = GlobalConfig.getInstance();
                String configValue = config.getConfigValue();
                out.output(configValue + ": " + input);
            }
        }));

        pipeline.run().waitUntilFinish();
    }
}