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MapReduce提供的inputformat输入类型并不能满足我们的使用需求,因此,mapreduce可以由用户自定义inputformat逻辑来处理各类数据。
步骤:
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将多个小文件合并成一个SequenceFile文件(SequenceFile文件是Hadoop用来存储二进制形式的key-value对的文件格式),
SequenceFile里面存储着多个文件,存储的形式为文件路径+名称为key,文件内容为value。
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可以看到在下面的代码实例中我们自定义了一个继承FileInputFormat类的WholeFileInputFormat类用来实现以文件整体作为输入的input format,并在其中重写了RecordReader对象将文件内容转换为ByteWritable来封装到Value中去,最终通过reducer自带的功能将这些小文件全部整合写入到一个文件中去。在Driver驱动类中设置自定义的InputFormat类:
job.setInputFormatClass(WholeFileInputformat.class);
注意这样合并小文件的方式实际上就是每个小文件mapreduce都会开启一个maptask来处理一个小文件。
package com.IN.mat;import java.io.IOException;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.BytesWritable;import org.apache.hadoop.io.NullWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.InputSplit;import org.apache.hadoop.mapreduce.JobContext;import org.apache.hadoop.mapreduce.RecordReader;import org.apache.hadoop.mapreduce.TaskAttemptContext;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;// 定义类继承FileInputFormatpublic class WholeFileInputformat extends FileInputFormat{ @Override protected boolean isSplitable(JobContext context, Path filename) { return false; } @Override public RecordReader createRecordReader(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException { WholeRecordReader recordReader = new WholeRecordReader(); recordReader.initialize(split, context); return recordReader; }}
package com.IN.mat;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.BytesWritable;import org.apache.hadoop.io.IOUtils;import org.apache.hadoop.io.NullWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.InputSplit;import org.apache.hadoop.mapreduce.RecordReader;import org.apache.hadoop.mapreduce.TaskAttemptContext;import org.apache.hadoop.mapreduce.lib.input.FileSplit;public class WholeRecordReader extends RecordReader{ private Configuration configuration; private FileSplit split; private boolean isProgress= true; private BytesWritable value = new BytesWritable(); private Text k = new Text(); @Override public void initialize(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException { this.split = (FileSplit)split; configuration = context.getConfiguration(); } @Override public boolean nextKeyValue() throws IOException, InterruptedException { if (isProgress) { // 1 定义缓存区 byte[] contents = new byte[(int)split.getLength()]; FileSystem fs = null; FSDataInputStream fis = null; try { // 2 获取文件系统 Path path = split.getPath(); fs = path.getFileSystem(configuration); // 3 读取数据 fis = fs.open(path); // 4 读取文件内容 IOUtils.readFully(fis, contents, 0, contents.length); // 5 输出文件内容 value.set(contents, 0, contents.length);// 6 获取文件路径及名称 String name = split.getPath().toString();// 7 设置输出的key值 k.set(name); } catch (Exception e) { }finally { IOUtils.closeStream(fis); } isProgress = false; return true; } return false; } @Override public Text getCurrentKey() throws IOException, InterruptedException { return k; } @Override public BytesWritable getCurrentValue() throws IOException, InterruptedException { return value; } @Override public float getProgress() throws IOException, InterruptedException { return 0; } @Override public void close() throws IOException { }}
Mapper,只需要将kv写入Context中即可
package com.IN.mat;import java.io.IOException;import org.apache.hadoop.io.BytesWritable;import org.apache.hadoop.io.NullWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.lib.input.FileSplit;public class SequenceFileMapper extends Mapper{ @Override protected void map(Text key, BytesWritable value,Context context) throws IOException, InterruptedException { context.write(key, value); }}
package com.IN.mat;import java.io.IOException;import org.apache.hadoop.io.BytesWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Reducer;public class SequenceFileReducer extends Reducer{ @Override protected void reduce(Text key, Iterable values, Context context) throws IOException, InterruptedException { context.write(key, values.iterator().next()); }}
package com.IN.mat;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.BytesWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;public class SequenceFileDriver { public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException { // 输入输出路径需要根据自己电脑上实际的输入输出路径设置 args = new String[] { "d:/mapreduceinput/input1", "d:/mapreduceoutput/output1" }; // 1 获取job对象 Configuration conf = new Configuration(); Job job = Job.getInstance(conf); // 2 设置jar包存储位置、关联自定义的mapper和reducer job.setJarByClass(SequenceFileDriver.class); job.setMapperClass(SequenceFileMapper.class); job.setReducerClass(SequenceFileReducer.class); // 7设置输入的inputFormat job.setInputFormatClass(WholeFileInputformat.class); // 8设置输出的outputFormat job.setOutputFormatClass(SequenceFileOutputFormat.class); // 3 设置map输出端的kv类型 job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(BytesWritable.class); // 4 设置最终输出端的kv类型 job.setOutputKeyClass(Text.class); job.setOutputValueClass(BytesWritable.class); // 5 设置输入输出路径 FileInputFormat.setInputPaths(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); // 6 提交job boolean result = job.waitForCompletion(true); System.exit(result ? 0 : 1); }}
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