Image processing 如何将Hadoop中的SequenceFile转换为图像文件？以下代码返回错误（bImageFromConvert为空）

/*将序列文件转换为图像 正在使用的序列文件是从图像生成的序列文件。png格式*/

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.File;
import javax.imageio.ImageIO;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;



public class SeqToImage {

//序列文件的键是图像名称，值是图像内容

public static void main(String args[]) throws Exception {

        Configuration confHadoop = new Configuration();       
        FileSystem fs = FileSystem.get(confHadoop);
        Path inPath = new Path("/home/Desktop/1.seq");
        SequenceFile.Reader reader = new SequenceFile.Reader(fs, inPath, confHadoop);
        Writable key = (Writable)
        ReflectionUtils.newInstance(reader.getKeyClass(), confHadoop);
        Writable value = (Writable)
        ReflectionUtils.newInstance(reader.getValueClass(), confHadoop);
        reader.next(key,value);

//输出是一些字节数，这意味着b不是空的

  System.out.println("KEY "+key.toString());
            byte[] b = Bytes.toBytes(value.toString());
            System.out.println(b.length);

//由于bImageFromConvert为空，以下行返回错误

BufferedImage bImageFromConvert = ImageIO.read(new ByteArrayInputStream(b));

您的值（图像）应为BytesWritable。你应该像这样投：

System.out.println((bImageFromConvert.toString()).length());
        ImageIO.write(bImageFromConvert, "png", new File(
                "/home/Desktop/imageAgain.png"));
        }
    }

第二，您应该使用copyBytes（）而不是Bytes.toBytes

它给出的字节副本正好是数据的长度。 所以这应该行得通

     BytesWritable value = (BytesWritable)
    ReflectionUtils.newInstance(reader.getValueClass(), confHadoop);

---

这将完成

序列文件中的实际键和值类型是什么？键类型是文本，值类型是BytesWritable如果使用getKeyClass方法，为什么需要使用强制转换？i、 e.

（IntWritable）reader.getKeyClass（）.newInstance（）在我的示例中，它不是已经是可写的了吗？谢谢
    Configuration confHadoop = new Configuration();       
    FileSystem fs = FileSystem.get(confHadoop);
    Path inPath = new Path("/home/Desktop/1.seq");
    SequenceFile.Reader reader = new SequenceFile.Reader(fs, inPath, confHadoop);
    //Name of your Image
    Text key = (Text)
    ReflectionUtils.newInstance(reader.getKeyClass(), confHadoop);
    // Value -- mage
    BytesWritable value = (BytesWritable)
    ReflectionUtils.newInstance(reader.getValueClass(), confHadoop);
    reader.next(key,value);
    .......
                byte[] b = copyBytes(value) ;

    System.out.println((bImageFromConvert.toString()).length());
    ImageIO.write(bImageFromConvert, "png", new File(
            "/home/Desktop/imageAgain.png"));
    }
}