Getinputformat), which is the Fileinputformat subclass of the special class, And Fileinputformat is the InputFormat subclass. With this kind of relationship we can easily understand that the default file format is a text file, and the key is the longwritable type (shaping number), the value is the text type (string). Just knowing the file type is not enough, we also need to separate each piece of data in the file into a key-value pair, this work is recordreader to do. In the Getrecordreader met
Mapmap read files in different formats This problem has always been, the previous reading method is to get the name of the file in the map, according to the name of different ways to read, such as the following wayFetch file name Inputsplit Inputsplit = Context.getinputsplit (); String FileName = ((filesplit) inputsplit). GetPath (). toString (), if (Filename.contains ("track")) {} else if ( Filename.contains ("complain3")) {}There are two problems in
InputFormat returned3.InputFormat: Class Hierarchy3.1FileInputFormat:Fileinputformat is a subclass of InputFormat, and all input format classes that use files as data sources inheritSince it---implements the Getsplits methodThe type of shard returned by the---is filesplit, which is a subclass of Inputsplit, with the description file path added, the Shard start positionof information--- does not implement the Createrecordreader method, is an abstract
Document directory
Accept
You can use the third parameter of the override map function. The map function is as follows:Public void map (longwritable key, text value, outputcollector
String Path = (filesplit) reporter. getinputsplit (). getpath (). tostring ();
To obtain the full path.
The following method can be used to select files:
Public ClassFilterImplementsPathfilter {Public BooleanAccept (Path ){Return! (Path. tostring (). indexof ("ABC")
= in. read (buffer); If (bufferlength
2. according to the preceding behavior of Readline, when a cross-split row is encountered, the data will continue to be read until the end of the row in the next split, so how does one determine whether the first line of the next split has been read by the linerecordreader of the previous split to avoid missing or repeated reading of the first line? In this regard, linerecordreader uses a simple and clever method:Since it cannot be determined whether a ro
Package namespace; import Java. io. *; public class study {Private Static int size = 1024; // you can set the size of the file to be read at a time./** file cutting ** string path: Path to the cut file * size: size of the sub-file **/public static void filesplit (string path, int size) throws exception {If (Path = NULL) throw new exception ("the source file cannot be empty... "); file = new file (PATH); If (! File. exists () throw new exception ("the
use other statements to operate strings.5). Condense: Remove spaces from the string.Condense {c} [no-gaps].:Purpose: remove the leading and trailing spaces in the string. If no-gaps is specified, remove all spaces in the string.Common Use Case: obtain the exact length of a string for determination.6). Split: Split stringSplit {c} At {del} into {C1}... {CN }.Purpose: Split string C into C1 according to the delimiters... CN.Split {c} At {del} into table {itab }.Purpose: Split C by the delimiters
Original article: http://wiki.apache.org/lucene-hadoop/HadoopMapReduce
Keyword:Filesplit: a subset of a file-the object segmentation body.
Introduction:
This document describes how map and reduce operations are completed in hadoop. If you are not familiar with Google's mapreduce patterns, see mapreduce-http://labs.google.com/papers/mapreduce.html first
Map
Since map operates the input file set in parallel, its first step (filesplit) is to divide the f
To partition large files in Linux , such as a 5GB log file, it is necessary to divide it into smaller files, which are segmented to facilitate reading by the normal text editor.Sometimes, the need to transfer large files of 20gb ,Linux training Tutorial pieces to another server, you also need to split it into multiple files, which makes it easy to transfer data.The following five different examples, to explain how to partition large files under Linux for your reference.Example 1, separated by ea
The two-level copy command is used in the combination. Can be combined with a number of files, in fact, the total length of the test command line can theoretically achieve a combination of infinite split file, but the practical value is not high, millions more than a single document This single-threaded method appears inefficient, and should use more excellent algorithm for segmentation and combination.
This procedure can only be categorized as "toys".
Using System;
Using System.Drawing;
Using
Use MapReduce to create reverse indexes in parallel. If you enter a text file, the output is a tuple list, and each tuple consists of a data and a list of files that contain that data. The general approach involves connecting the data together and performing a connection operation in memory. However, with a large amount of data to perform operations, it is possible to consume memory or use database mediation storage tools, but this can reduce operational efficiency.
A better approach would be to
can be filtered to be small to fit in memory.
the job's main function sets the cache file (that is, the filter condition)
# Connect with map end
Mapper The Setup method to read the cache file
# Connect with map End
# Generate filter Set Joinkeyset
data filtering in the Mapper map method
@Override protected void Map (Object key, Text value, Context context) throws IOException, Interruptedexception
{//Get file input path String pathName = ((filesplit
Tags: client div way automatic about byte meaning image conditionThe spilt command is used to split a file into a number ofBy default, each 1000 is cut into a small fileSplit [-parameter] [file to be cut] [output FILENAME]Parameters-[Number of rows] Specify how many lines to cut into a small file-B bytes Specify how many bytes to cut into a small file-C is similar to the parameter "-B", but maintains the integrity of each line as much as possible duri
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