HDFS的IO操作（Java代码）

「爱情、让人受尽委屈。」 2022-05-29 10:42 177阅读 0赞

### HDFS的IO操作 ###

#### 1. 通过URL读取HDFS中的数据 ####

public class URLCat {
        private static final String HDFS_PATH = "hdfs://localhost:9000/user/zhang/test/README.txt";
    
        static {
            URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
        }
    
        public static void main(String[] args) {
            InputStream inputStream = null;
            try {
                inputStream = new URL(HDFS_PATH).openStream();
                IOUtils.copyBytes(inputStream, System.out, 4096, false);
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                IOUtils.closeStream(inputStream);
            }
        }
    }

#### 2. 通过FileSystem的方式获取文件—-FSDataInputStream ####

class FileSystemCat {
        private static final String HDFS_URI = "hdfs://localhost:9000";
        private static final String PATH = "/user/zhang/test/README.txt";
    
        public static void main(String[] args) throws IOException {
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), new Configuration());
            FSDataInputStream inputStream = fileSystem.open(new Path(PATH));
            IOUtils.copyBytes(inputStream, System.out, 4096, false);
            IOUtils.closeStream(inputStream);
        }
    }

#### 3. FSDataInputStream的seek(position)使用 ####

public class FileSystemDoubleCat {
        public static final String HDFS_URI = "hdfs://localhost:9000";
        public static final String PATH = "/user/zhang/test/README.txt";
    
        public static void main(String[] args) throws IOException {
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), new Configuration());
            FSDataInputStream inputStream = fileSystem.open(new Path(PATH));
            IOUtils.copyBytes(inputStream, System.out, 4096, false);
            // 回到文件开始位置
            inputStream.seek(0);
            IOUtils.copyBytes(inputStream, System.out, 4096, false);
            IOUtils.closeStream(inputStream);
        }
    }

#### 4. 将HDFS中的文件复制到另一个位置—-FSDataOutputStream 与 Progressable ####

public class FileCopyWirteProgress {
        public static final String HDFS_URI = "hdfs://localhost:9000";
        public static final String SRC_PATH = "/user/zhang/test/README.txt";
        public static final String DESC_PATH = "/user/zhang/test/abc.txt";
    
        public static void main(String[] args) throws IOException {
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), new Configuration());
            FSDataInputStream inputStream = fileSystem.open(new Path(SRC_PATH));
            # Progressable记录文件写入过程，做标记
            FSDataOutputStream outputStream = fileSystem.create(new Path(DESC_PATH), new Progressable() {
                public void progress() {
                    System.out.println("正在读取，请稍后...");
                }
            });
            IOUtils.copyBytes(inputStream, outputStream, 4096, true);
        }
    }

#### 5. ListStatus 列出文件路径 ####

public class ListStatus {
        public static final String HDFS_URI = "hdfs://localhost:9000";
    
        public static void main(String[] args) throws URISyntaxException, IOException {
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), new Configuration());
            Path path = fileSystem.getHomeDirectory();
            System.out.println("home path: " + path.getName());
            FileStatus[] fileStatuses = fileSystem.listStatus(path, new PathFilter() {
                public boolean accept(Path path) {
                    System.out.println("raw path: " + path);
                    if (path.toString().contains("test")) {
                        System.out.println("-----------------------");
                        return true;
                    }
                    return false;
                }
            });
            Path[] paths = FileUtil.stat2Paths(fileStatuses);
            for (Path p : paths) {
                System.out.println("path: " + p);
            }
        }
    }

#### 6. Compressor 压缩 ####

public class EncodeCompressor { 
        public static final String HDFS_URI = "hdfs://localhost:9000";
        public static final String PATH = "/user/zhang/test/README.txt";
    
        public static void main(String[] args) throws IOException {
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), new Configuration());
            FSDataInputStream inputStream = fileSystem.open(new Path(PATH));
            CompressionCodec codec = new GzipCodec();
            CompressionOutputStream outputStream = codec.createOutputStream(new FileOutputStream("README.txt.gz"));
            IOUtils.copyBytes(inputStream, outputStream, 4096, true);
        }
    }

#### 7. Decompressor 解压缩 ####

public class DecodeDecompressor { 
    
        public static final String HDFS_URI = "hdfs://localhost:9000";
        public static final String PATH = "/user/zhang/test/README.txt.gz";
    
        public static void main(String[] args) throws IOException {
            Configuration configuration = new Configuration();
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), configuration);
            Path path = new Path(PATH);
            FSDataInputStream inputStream = fileSystem.open(path);
            CompressionCodecFactory factory = new CompressionCodecFactory(configuration);
            CompressionCodec codec = factory.getCodec(path);
            if (codec != null) {
                CompressionInputStream compressionInputStream = codec.createInputStream(inputStream);
                IOUtils.copyBytes(compressionInputStream, new FileOutputStream("readme.txt"), 4096, true);
            }
    
        }
    }

#### 8. CodecPool 压缩池 ####

public class CodecPoolTest { 
        public static final String HDFS_URI = "hdfs://localhost:9000";
        public static final String DE_PATH = "/user/zhang/test/README.txt.gz";
        public static final String EN_PATH = "/user/zhang/test/README.txt";
    
        public static void main(String[] args) throws IOException {
            en();
            de();
        }
    
        public static void en() throws IOException {
            Configuration configuration = new Configuration();
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), configuration);
            Path path = new Path(EN_PATH);
            FSDataInputStream inputStream = fileSystem.open(path);
            CompressionCodecFactory factory = new CompressionCodecFactory(configuration);
            CompressionCodec codec = new GzipCodec();
            Compressor compressor = CodecPool.getCompressor(codec);
            CompressionOutputStream outputStream = codec.createOutputStream(new FileOutputStream("en_readme.txt.gz"), compressor);
            IOUtils.copyBytes(inputStream, outputStream, 4096, true);
        }
    
        public static void de() throws IOException {
            Configuration configuration = new Configuration();
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), configuration);
            Path path = new Path(DE_PATH);
            FSDataInputStream inputStream = fileSystem.open(path);
            CompressionCodecFactory factory = new CompressionCodecFactory(configuration);
            CompressionCodec codec = factory.getCodec(path);
            Decompressor decompressor = CodecPool.getDecompressor(codec);
            CompressionInputStream codecInputStream = codec.createInputStream(inputStream, decompressor);
            IOUtils.copyBytes(codecInputStream, new FileOutputStream("de_readme.txt"), 4096, true);
        }
    }

#### 9. SequeneceFile 写入和读取数据 ####

public class SequenceFileDemo {
        public static String[] strings = new String[]{
       "hello", "java", "python", "hadoop", "scala"};
        public static final String HDFS_URI = "hdfs://localhost:9000";
        public static final String PATH = "/user/zhang/test/sequenceFile.txt";
    
        public static void main(String[] args) throws IOException {
            writeSeqenceFile();
    // readSeqenceFile();
        }
    
        private static void readSeqenceFile() throws IOException {
            Configuration configuration = new Configuration();
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), configuration);
            SequenceFile.Reader reader = new SequenceFile.Reader(fileSystem, new Path(PATH), configuration);
            Class<?> keyClass = reader.getKeyClass();
            Class<?> valueClass = reader.getValueClass();
            Writable key = (Writable) ReflectionUtils.newInstance(keyClass, configuration);
            Writable value = (Writable) ReflectionUtils.newInstance(valueClass, configuration);
            long position = 0;
            while (reader.next(key, value)) {
                String s = reader.syncSeen() ? "*" : "";
                System.out.println(position + " syncSeen: " + s + " key: " + key + " value: " + value);
                position = reader.getPosition();
            }
            IOUtils.closeStream(reader);
        }
    
        private static void writeSeqenceFile() throws IOException {
            Configuration configuration = new Configuration();
            FileSystem fileSystem = FileSystem.get(URI.create(HDFS_URI), configuration);
            IntWritable key = new IntWritable();
            Text value = new Text();
            SequenceFile.Writer writer = SequenceFile.createWriter(fileSystem, configuration, new Path(PATH), key.getClass(), value.getClass());
            for (int i = 0; i < 100; i++) {
                key.set(100 - i);
                value.set(strings[i % strings.length]);
                System.out.println(writer.getLength() + " key: " + key + " value: " + value);
                writer.append(key, value);
            }
            IOUtils.closeStream(writer);
        }
    }