Hadoop中的FileStatus、BlockLocation、LocatedBlocks、InputSplit

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1 FileStatus

1.1 包名
org.apache.hadoop.fs.FileStatus

1.2 格式

FileStatus{path=hdfs://192.X.X.X:9000/hadoop-2.7.1.tar.gz; isDirectory=false; length=210606807; replication=3; blocksize=134217728; modification_time=xxx; access_time=xxx; owner=xxx; group=supergroup; permission=rw-r--r--; isSymlink=false}

2 BlockLocation

2.1 包名
org.apache.hadoop.fs.BlockLocation

2.2 调用处
JobClient的writeNewSplits方法，其中调用了List<InputSplit> splits = input.getSplits(job)方法，在getSplits方法中调用了getFileLocation()。

2.3 格式

public static void getFileLocation() throws Exception {    Configuration conf = new Configuration();Path fpath = new Path(AConstants.hdfsPath + "hadoop-2.7.1.tar.gz");FileSystem hdfs = fpath.getFileSystem(conf);FileStatus filestatus = hdfs.getFileStatus(fpath);BlockLocation[] blkLocations = hdfs.getFileBlockLocations(filestatus,0, filestatus.getLen());System.out.println("total block num:" + blkLocations.length);for (int i = 0; i < blkLocations.length; i++) {System.out.println(blkLocations[i].toString());System.out.println("文件在block中的偏移量" + blkLocations[i].getOffset()                + ", 长度" + blkLocations[i].getLength());}}

total block num:2
0,134217728,192.X.X.X
文件在block中的偏移量0, 长度134217728
134217728,76389079,192.X.X.X
文件在block中的偏移量134217728, 长度76389079

splits数组信息

int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining);splits.add(makeSplit(path, length-bytesRemaining,splitSize,blkLocations[blkIndex].getHosts(),blkLocations[blkIndex].getCachedHosts()));

[hdfs://192.x.x.x:9000/hadoop-2.7.1.tar.gz:0+134217728,
hdfs://192.x.x.x:9000/hadoop-2.7.1.tar.gz:134217728+31987190]

3 LocatedBlocks

3.1 包名
org.apache.hadoop.hdfs.protocol.LocatedBlocks

3.2 调用处
在hdfs读取文件时调用openInfo()方法，最终调用的是DFSInputStream的fetchLocatedBlocksAndGetLastBlockLength方法获取块信息LocatedBlocks。块的信息非常详尽，如块名称，大小，起始偏移量，IP地址等。

在hadoop中写文件实际是把block写入到datanode中，而namenode是通过datanode定期的汇报得知该文件到底由哪几个block组成的。因此在读某个文件时可能存在datanode还未汇报给namenode的情况，因此在读文件时只能读到最后一个汇报的block块。isLastBlockComplete可以标识是否读取到最后的块。若不是则会根据元数据提供的block的pipeline来到datanode上获得block的写入长度，并赋值给lastBlockBeingWrittenLength。

3.3 格式

LocatedBlocks {fileLength = 210606807underConstruction = falseblocks = [LocatedBlock {BP - 1853423215 - 192.X.X.X - 1474747765776: blk_1073741828_1004;getBlockSize() = 134217728;corrupt = false;offset = 0;locs = [192.X.X.X: 50010]}, LocatedBlock {BP - 1853423215 - 192.X.X.X - 1474747765776: blk_1073741829_1005;getBlockSize() = 76389079;corrupt = false;offset = 134217728;locs = [192.X.X.X: 50010]}]lastLocatedBlock = LocatedBlock {BP - 1853423215 - 192.X.X.X - 1474747765776: blk_1073741829_1005;getBlockSize() = 76389079;corrupt = false;offset = 134217728;locs = [192.X.X.X: 50010]}isLastBlockComplete = true}

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