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 = 210606807
underConstruction = false
blocks = [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
}
