使用 DataOutputStream 写入文件的 Java 不起作用

Question

I have a task to write the data in one file into another using the ByteStream. What I'm trying to do is to read data in from file a.txt and write into a2.txt.

The read part works, but the write part does not work. I'm not getting an error, but there is no data in the a2.txt.

What am I doing wrong here?

public static void main (String[] args) throws IOException
{
        String oldfile = "/Users/xy/Desktop/Java/a.txt";
        String newfile = "/Users/xy/Desktop/Java/a2.txt";

        inputoutput(oldfile,newfile);
}

public static void inputoutput(String alt, String neu) throws IOException{
    
    //InputStream
    FileInputStream fiStream = new FileInputStream(alt);
    DataInputStream diStream = new DataInputStream(fiStream);

    //Creating a Array in size of the File 
    byte[] daten = new byte [diStream.available()];
    // Save filesize
    int eingabeDatensize = diStream.available();
    diStream.read(daten);

    // Test if input works 
    for (int i = 0; i < eingabeDatensize; i++){
        System.out.println(daten[i]);
    }
    diStream.close();

    //OutputStream

    FileOutputStream foStream = new FileOutputStream(neu);
    DataOutputStream doStream = new DataOutputStream(foStream);
    
    //Creating a Array in size of the input file  
    byte[] ausgabedaten = new byte[eingabeDatensize];

    //Writing the data into the Array
    for (int i = 0; i < eingabeDatensize; i++){
        doStream.write(ausgabedaten[i]);
    }
    doStream.close();
    System.out.println("Successfull");
}

Answer 1

Try this hope it will work.

public static void inputoutput(String alt, String neu) throws IOException{


//InputStream
FileInputStream fiStream = new FileInputStream(new File(alt));
DataInputStream diStream = new DataInputStream(fiStream);

//Creating a Array in size of the File 
byte[] daten = new byte [diStream.available()];
// Save filesize
int eingabeDatensize = diStream.available();
diStream.read(daten);

// Test if input works 
for (int i = 0; i < eingabeDatensize; i++){
    System.out.println(daten[i]);
}
diStream.close();

//OutputStream

FileOutputStream foStream = new FileOutputStream(neu);
DataOutputStream doStream = new DataOutputStream(foStream);


//Writing the data into the Array
for (int i = 0; i < eingabeDatensize; i++){
    doStream.write(daten[i]);
}
doStream.close();
System.out.println("Successfull");
}