3.查看Java帮助手册或其他资料,用"java.net.URL"和"org.apache.hadoop.fs.FsURLStreamHandlerFactory”编程来输出 HDFS 中指定文件的文本到终端中。

以下是使用Java的`java.net.URL`和`org.apache.hadoop.fs.FsURLStreamHandlerFactory`类来从HDFS中读取指定文件的文本并输出到终端的代码示例：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import org.apache.hadoop.fs.FsUrlStreamHandlerFactory;

public class HdfsFileReader {

    public static void main(String[] args) throws Exception {
        
        // Register the HDFS URL stream handler factory
        URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
        
        // Specify the HDFS URL of the file to read
        String hdfsUrl = "hdfs://localhost:9000/path/to/file.txt";
        
        // Create a URL object representing the HDFS file
        URL url = new URL(hdfsUrl);
        
        // Open a connection to the HDFS file and create a BufferedReader to read its contents
        BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
        
        // Read the contents of the file line by line and print them to the console
        String line;
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
        
        // Close the BufferedReader and the HDFS file connection
        reader.close();
    }
}

请注意，此代码需要Hadoop客户端库和配置文件来运行。在运行此代码之前，请确保您已正确配置了Hadoop，并将其放在`CLASSPATH`中。