Appending content of binary files

Question

I want to append the content of one file to another existing file with content. I used plain file copy with FileOutputStream with append parameter and also with SequenceInputStream. Both are working for txt files but not for binary files like pdf and excel.

If i try to merge two pdf files always the second input stream is overwritten in the resultant file. Is there any other way i can achieve the same for binary files ?

Below is my code.

package org.saurav.simpletests.io;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.SequenceInputStream;

public class ConcatStreams {
    
    public static void main (String a[]) {
        
        ConcatStreams concatStreams = new ConcatStreams();
        
        
        try {
            InputStream  input1 = new FileInputStream("<path to first binary file>");
            InputStream input2 = new FileInputStream("<path to second binary file>");
            
            OutputStream  output = new FileOutputStream("<path to first binary file> ",true);
            //concatStreams.mergeUsingSequenctInputStream(input1,input2); // uncomment it to run the code with sequenceInputStream
            concatStreams.mergeUsingFileOutputAppend(output, input2);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        
        
    }
    
    private void mergeUsingFileOutputAppend(OutputStream outStream, InputStream input) {
        
        
        try {
            byte[] buffer = new byte[256];
            int data;
            
                data = input.read(buffer);
                while(data != -1){
                    String str = new String(buffer, "UTF-8");
                    //System.out.println(str);
                    outStream.write(buffer);
                    data = input.read(buffer);
                    
                }
            
           //output.write(data);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
           try {
            outStream.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        }
    }
    
    private void mergeUsingSequenctInputStream(InputStream input1, InputStream input2) {
        
        

        SequenceInputStream sequenceInputStream =
            new SequenceInputStream(input1, input2);
        FileOutputStream fos = null;
        try {
        fos = new FileOutputStream("<path to first binary file>");
        byte[] buffer = new byte[256];
        int data;
        
            data = sequenceInputStream.read(buffer);
            while(data != -1){
                String str = new String(buffer, "UTF-8");
                //System.out.println(str);
                fos.write(buffer);
                data = sequenceInputStream.read(buffer);
                
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                fos.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        
        
    }

}

Best Regards, Saurav

Answer 1

There is a bug in your implementation: you always write fixed chunks of bytes (equal to the size of buffer) to output stream, please take attention to this line:

outStream.write(buffer);

Please take into account that input stream might have a remainder that is less than buffer size. The fix should be using the following line:

outStream.write(buffer, 0, data);

I've updated your code like this and was able to join jpeg file that was split into 2 parts.