序列文件的读取和写入

1、序列文件（二进制）的写入

    /**
     * 写入文件
     * @throws IOException
     */
    @Test
    public void save() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Writer writer = SequenceFile.createWriter(fs, conf, path, IntWritable.class, Text.class);
        for(int i = 0; i < 100; i++){
            writer.append(new IntWritable(i),new Text("hello" + i));
        }
        writer.close();
    }

读取序列文件
D:sequence>hdfs dfs -text file:///d:/sequence/1.seq
18/01/04 11:15:20 WARN zlib.ZlibFactory: Failed to load/initialize native-zlib library
18/01/04 11:15:20 INFO compress.CodecPool: Got brand-new decompressor [.deflate]
0       hello0
1       hello1
2       hello2
3       hello3
4       hello4
5       hello5
6       hello6
7       hello7

2、序列文件的读取

/**
     * 读取文件
     * @throws IOException
     */
    @Test
    public void read() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Reader reader =  new SequenceFile.Reader(fs,path,conf);
        IntWritable key = new IntWritable();
        Text value = new Text();
        while (reader.next(key,value)){
            System.out.println(key.get() + "===>" + value.toString());
        }
    }

    /**
     * 读取文件2
     * @throws IOException
     */
    @Test
    public void read2() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Reader reader =  new SequenceFile.Reader(fs,path,conf);
        IntWritable key = new IntWritable();
        Text value = new Text();
        while (reader.next(key)){
            reader.getCurrentValue(value);
            System.out.println(key.get() + "===>" + value.toString());
        }
    }

3、读取文件指针

/**
     * 读取文件指针
     * @throws IOException
     */
    @Test
    public void read2() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Reader reader =  new SequenceFile.Reader(fs,path,conf);
        long pos = reader.getPosition();
        System.out.println("文件指针：" + pos);
        IntWritable key = new IntWritable();
        Text value = new Text();
        while (reader.next(key)){
            System.out.println("文件指针：" +  reader.getPosition());
            reader.getCurrentValue(value);
            System.out.println(key.get() + "===>" + value.toString());
        }
    }


4、增加同步点

 /**
     * 写入文件
     * @throws IOException
     */
    @Test
    public void save() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Writer writer = SequenceFile.createWriter(fs, conf, path, IntWritable.class, Text.class);
        for(int i = 0; i < 10; i++){
            writer.append(new IntWritable(i),new Text("hello" + i));
            writer.sync();
        }
        for(int i = 0; i < 10; i++){
            writer.append(new IntWritable(i),new Text("hello" + i));
            if(i % 2 ==0) writer.sync();
        }
        writer.close();
    }

文件指针：128
文件指针：155===>0===>hello0
文件指针：202===>1===>hello1
文件指针：249===>2===>hello2
文件指针：296===>3===>hello3
文件指针：343===>4===>hello4
文件指针：390===>5===>hello5
文件指针：437===>6===>hello6
文件指针：484===>7===>hello7
文件指针：531===>8===>hello8
文件指针：578===>9===>hello9
文件指针：625===>0===>hello0
文件指针：672===>1===>hello1
文件指针：699===>2===>hello2
文件指针：746===>3===>hello3
文件指针：773===>4===>hello4
文件指针：820===>5===>hello5
文件指针：847===>6===>hello6
文件指针：894===>7===>hello7
文件指针：921===>8===>hello8
文件指针：968===>9===>hello9

5、操作同步点

 /**
     * 读取文件指针，操纵同步点
     * @throws IOException
     */
    @Test
    public void readsync() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Reader reader =  new SequenceFile.Reader(fs,path,conf);
        long pos = reader.getPosition();
        System.out.println("文件头部指针：" + pos);
        IntWritable key = new IntWritable();
        Text value = new Text();
        //指定读取的开始点
        reader.seek(155);
//        reader.seek(237);
//        reader.sync(209);
        while (reader.next(key)){
            reader.getCurrentValue(value);
            System.out.println("文件指针：" +  reader.getPosition()+"===>"+key.get() + "===>" + value.toString());
        }
    }
文件头部指针：128
文件指针：202===>1===>hello1
文件指针：249===>2===>hello2
文件指针：296===>3===>hello3
文件指针：343===>4===>hello4
文件指针：390===>5===>hello5
文件指针：437===>6===>hello6
文件指针：484===>7===>hello7
文件指针：531===>8===>hello8
文件指针：578===>9===>hello9
文件指针：625===>0===>hello0
文件指针：672===>1===>hello1
文件指针：699===>2===>hello2
文件指针：746===>3===>hello3
文件指针：773===>4===>hello4
文件指针：820===>5===>hello5
文件指针：847===>6===>hello6
文件指针：894===>7===>hello7
文件指针：921===>8===>hello8
文件指针：968===>9===>hello9

6、如果没有对应的指针，使用sync()

/**
     * 读取文件指针，操纵同步点
     * @throws IOException
     */
    @Test
    public void readsync() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Reader reader =  new SequenceFile.Reader(fs,path,conf);
        long pos = reader.getPosition();
        System.out.println("文件头部指针：" + pos);
        IntWritable key = new IntWritable();
        Text value = new Text();
        //指定读取的开始点
//        reader.seek(250);
//        reader.seek(237);
        reader.sync(344);
        while (reader.next(key)){
            reader.getCurrentValue(value);
            System.out.println("文件指针：" +  reader.getPosition()+"===>"+key.get() + "===>" + value.toString());
        }
    }

文件头部指针：128
文件指针：437===>6===>hello6
文件指针：484===>7===>hello7
文件指针：531===>8===>hello8
文件指针：578===>9===>hello9
文件指针：625===>0===>hello0
文件指针：672===>1===>hello1
文件指针：699===>2===>hello2
文件指针：746===>3===>hello3
文件指针：773===>4===>hello4
文件指针：820===>5===>hello5
文件指针：847===>6===>hello6
文件指针：894===>7===>hello7
文件指针：921===>8===>hello8
文件指针：968===>9===>hello9

7、一边写入一边压缩

 /**
     * 写入文件
     * @throws IOException
     */
    @Test
    public void save() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "file:///");
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("D:\sequence\1.seq");
        SequenceFile.Writer writer = SequenceFile.createWriter(fs, conf, path, IntWritable.class, Text.class, SequenceFile.CompressionType.RECORD,new GzipCodec());
        for(int i = 0; i < 10; i++){
            writer.append(new IntWritable(i),new Text("hello" + i));
            writer.sync();
        }
        for(int i = 0; i < 10; i++){
            writer.append(new IntWritable(i),new Text("hello" + i));
            if(i % 2 ==0) writer.sync();
        }
        writer.close();
    }









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原文地址：https://www.cnblogs.com/flyingcr/p/10326974.html