上一例是直接用SequenceFile的createWriter来实现，本例采用mapreduce的方式。
1、把小文件整体读入需要自定义InputFormat格式，自定义InputFormat格式需要先定义RecordReader读取方式，为了整体读入，RecordReader使用一次性读入所有字节。
1.1 继承RecordReader泛型，重写这个类。
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.mapreduce.InputSplit; import org.apache.hadoop.mapreduce.RecordReader; import org.apache.hadoop.mapreduce.TaskAttemptContext; import org.apache.hadoop.mapreduce.lib.input.FileSplit; import java.io.IOException; public class WholeFileRecordReader extends RecordReader<NullWritable,BytesWritable> { private FileSplit fileSplit; private Configuration conf; private BytesWritable value = new BytesWritable(); private boolean processed = false; /** * Called once at initialization. * * @param split the split that defines the range of records to read * @param context the information about the task * @throws IOException * @throws InterruptedException */ @Override public void initialize(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException { this.fileSplit = (FileSplit) split; this.conf = context.getConfiguration(); } /** * Read the next key, value pair. * * @return true if a key/value pair was read * @throws IOException * @throws InterruptedException */ @Override public boolean nextKeyValue() throws IOException, InterruptedException { if(!processed){ byte[] contents = new byte[(int)fileSplit.getLength()]; Path file = fileSplit.getPath(); FileSystem fs = file.getFileSystem(conf); FSDataInputStream in = null; try { in = fs.open(file); IOUtils.readFully(in,contents,0,contents.length);//一次全部读取 value.set(contents,0,contents.length); }finally { IOUtils.closeStream(in); } processed = true; return true; } return false; } /** * Get the current key * * @return the current key or null if there is no current key * @throws IOException * @throws InterruptedException */ @Override public NullWritable getCurrentKey() throws IOException, InterruptedException { return NullWritable.get(); } /** * Get the current value. * * @return the object that was read * @throws IOException * @throws InterruptedException */ @Override public BytesWritable getCurrentValue() throws IOException, InterruptedException { return value; } /** * The current progress of the record reader through its data. * * @return a number between 0.0 and 1.0 that is the fraction of the data read * @throws IOException * @throws InterruptedException */ @Override public float getProgress() throws IOException, InterruptedException { return processed ? 1.0f:0.0f; } /** * Close the record reader. */ @Override public void close() throws IOException { } }
1.2 继承FileInputFormat泛型，重写文件输入格式
import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.BytesWritable; import org.apache.hadoop.io.NullWritable; 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; import java.io.IOException; public class WholeFileInputFormat extends FileInputFormat<NullWritable,BytesWritable> { /** * Is the given filename splittable? Usually, true, but if the file is * stream compressed, it will not be. * <p> * The default implementation in <code>FileInputFormat</code> always returns * true. Implementations that may deal with non-splittable files <i>must</i> * override this method. * <p> * <code>FileInputFormat</code> implementations can override this and return * <code>false</code> to ensure that individual input files are never split-up * so that process entire files. * * @param context the job context * @param filename the file name to check * @return is this file splitable? */ @Override protected boolean isSplitable(JobContext context, Path filename) { return false;//文件不分片，为了整体读入 } /** * Create a record reader for a given split. The framework will call * {@link RecordReader#initialize(InputSplit, TaskAttemptContext)} before * the split is used. * * @param split the split to be read * @param context the information about the task * @return a new record reader * @throws IOException * @throws InterruptedException */ @Override public RecordReader<NullWritable, BytesWritable> createRecordReader(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException { WholeFileRecordReader recordReader = new WholeFileRecordReader(); recordReader.initialize(split,context); return recordReader; } }
2、MAPPER，不要写reduce，本例只是合并文件。
public class SequenceFileMapper extends Mapper<NullWritable,BytesWritable,Text,BytesWritable> { enum FileCounter { FILENUM } private Text filenameKey; /** * Called once at the beginning of the task. * * @param context */ @Override protected void setup(Context context) throws IOException, InterruptedException { InputSplit split = context.getInputSplit(); Path path = ((FileSplit)split).getPath(); filenameKey = new Text(path.toString()); } /** * Called once for each key/value pair in the input split. Most applications * should override this, but the default is the identity function. * * @param key * @param value * @param context */ @Override protected void map(NullWritable key, BytesWritable value, Context context) throws IOException, InterruptedException { context.write(filenameKey,value); //自定义计数器 context.getCounter(FileCounter.FILENUM).increment(1); //动态计数器 context.getCounter("FileNameList",filenameKey.toString()).increment(1); } }
3、执行job，使用辅助类Tool，也可以不用，直接写job执行就可以。
import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.conf.Configured; import org.apache.hadoop.fs.FileSystem; 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; import org.apache.hadoop.util.Tool; import org.apache.hadoop.util.ToolRunner; public class SmallFilesToSequenceFileConverter extends Configured implements Tool { /** * Execute the command with the given arguments. * * @param args command specific arguments. * @return exit code. * @throws Exception */ @Override public int run(String[] args) throws Exception { Configuration conf = getConf(); if(conf==null){ return -1; } Path outPath = new Path(args[1]); FileSystem fileSystem = outPath.getFileSystem(conf); //删除输出路径 if(fileSystem.exists(outPath)) { fileSystem.delete(outPath,true); } Job job = Job.getInstance(conf,"SmallFilesToSequenceFile"); job.setJarByClass(SmallFilesToSequenceFileConverter.class); job.setMapperClass(SequenceFileMapper.class); job.setInputFormatClass(WholeFileInputFormat.class); job.setOutputFormatClass(SequenceFileOutputFormat.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(BytesWritable.class); FileInputFormat.addInputPath(job,new Path(args[0])); FileOutputFormat.setOutputPath(job,new Path(args[1])); return job.waitForCompletion(true) ? 0:1; } public static void main(String[] args) throws Exception{ long startTime = System.currentTimeMillis(); int exitCode = ToolRunner.run(new SmallFilesToSequenceFileConverter(),args); System.exit(exitCode); long endTime = System.currentTimeMillis(); long timeSpan = endTime - startTime; System.out.println("运行耗时："+timeSpan+"毫秒。"); } }
4、上传集群运行，打包成jar包的时候把META-INF目录和src目录放同级，防止找不到函数入口。
#手动调整reduce数量为2，运算后会生成两个part [hadoop@bigdata-senior01 ~]$ hadoop jar SmallFilesToSequenceFileConverter.jar -D mapreduce.job.reduces=2 /demo /output3
...
[hadoop@bigdata-senior01 ~]$ hadoop fs -ls /output3
Found 3 items
-rw-r--r-- 1 hadoop supergroup 0 2019-02-18 16:17 /output3/_SUCCESS
-rw-r--r-- 1 hadoop supergroup 60072 2019-02-18 16:17 /output3/part-r-00000
-rw-r--r-- 1 hadoop supergroup 28520 2019-02-18 16:17 /output3/part-r-00001