Question

Is there a more efficient way to break the data in a byte array in Java?
I have written the following function to read a binary file with fixed length data field. But the performance are really slow, I need to read a binary file with 30,000 records each with the length of 300 bytes, and each record contain 240 fields.
Any advise?

public void breakField(byte[] input) {

    ByteArrayInputStream bais = new ByteArrayInputStream(input);

    byte[] tmp = new byte[2];
    bais.read(tmp);
    this.id = new String(tmp);

    tmp = new byte[4];
    bais.read(tmp);
    this.name = new String(tmp);

    tmp = new byte[8];
    bais.read(tmp);
    this.phone = new String(tmp);

    tmp = new byte[15];
    bais.read(tmp);
    this.otherInfo = new String(tmp);

    .... more fields...

}       

Answer 1

By reading the entire file into a byte[] array, if the file is larger than the amount of space available in memory to the JVM, then you will get an OutOfMemoryError.

Instead, you can use a BufferedReader in conjunction with a FileReader. This will allow you to read the file piece by piece without loading the entire thing into memory.

BufferedReader in = new BufferedReader(new FileReader("/path/to/my/file"));

To load the data record-by-record, simply read in 300 bytes at a time when you call BufferedReader.read. If you prefer to deal with individual fields, instead of reading 300 bytes at a time, just read the number of bytes that corresponds to the length of the next field.