How to chain multiple different InputStreams into one InputStream

Java provides 'SequenceInputStream' class, this is used to process collection of input streams in one shot.

'SequenceInputStream' provides below constructors.

SequenceInputStream(Enumeration<? extends InputStream> e)

SequenceInputStream(InputStream s1, InputStream s2)

Step 1: Create a SequenceInputStream from enumeration of input streams

InputStream inputStream1 = new FileInputStream(logFile1);

InputStream inputStream2 = new FileInputStream(logFile2);

InputStream inputStream3 = new FileInputStream(logFile3);

List<InputStream> inputStreams = Arrays.asList(inputStream1, inputStream2, inputStream3);

Enumeration<InputStream> e = Collections.enumeration(inputStreams);

Step 2: Now write the content to the file using SequenceInputStream.

try (OutputStream outputStream = new FileOutputStream(file)) {

         while ((noOfBytesRead = sequenceInputStream.read(buffer)) != -1) {

                  outputStream.write(buffer, 0, noOfBytesRead);

         }

}

Find the below working example.

FileUtil.java

package com.sample.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.SequenceInputStream;

public class FileUtil {

 private static final int BUFFER_SIZE = 4096;

 /**
  * Reads the data from multiple input streams and write to the file.
  * 
  * @param file
  * @param inputStreams
  * @throws IOException
  * @throws FileNotFoundException
  */
 public static void writeToFile(File file, SequenceInputStream sequenceInputStream)
   throws FileNotFoundException, IOException {
  if (file == null) {
   throw new IllegalArgumentException("file should not be null");
  }

  if (sequenceInputStream == null) {
   throw new IllegalArgumentException("sequenceInputStream can't be null");
  }

  byte[] buffer = new byte[BUFFER_SIZE];
  int noOfBytesRead;

  try (OutputStream outputStream = new FileOutputStream(file)) {
   while ((noOfBytesRead = sequenceInputStream.read(buffer)) != -1) {
    outputStream.write(buffer, 0, noOfBytesRead);
   }
  } finally {
   sequenceInputStream.close();
  }
 }

 public static void writeToFile(String filePath, SequenceInputStream sequenceInputStream)
   throws FileNotFoundException, IOException {
  writeToFile(new File(filePath), sequenceInputStream);
 }
}

Test.java

package com.sample.test;

import java.io.FileInputStream;
import java.io.InputStream;
import java.io.SequenceInputStream;
import java.util.Arrays;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;

import com.sample.util.FileUtil;

public class Test {
 public static void main(String args[]) throws Exception {
  String destinationPath = "C:\\Users\\krishna\\dest.log";

  String logFile1 = "C:\\Users\\krishna\\app1.log";
  String logFile2 = "C:\\Users\\krishna\\app2.log";
  String logFile3 = "C:\\Users\\krishna\\app3.log";

  InputStream inputStream1 = new FileInputStream(logFile1);
  InputStream inputStream2 = new FileInputStream(logFile2);
  InputStream inputStream3 = new FileInputStream(logFile3);

  List<InputStream> inputStreams = Arrays.asList(inputStream1, inputStream2, inputStream3);

  Enumeration<InputStream> e = Collections.enumeration(inputStreams);
  SequenceInputStream sequenceInputStream = new SequenceInputStream(e);

  FileUtil.writeToFile(destinationPath, sequenceInputStream);

 }
}

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