How to convert Map / Object to Bytes and save to internal storage and read back

package com.pkm;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.HashMap;
import java.util.Map;

/**
 *
 * @author PRITOM
 */
public class MapObjectToByteArrayAndSaveToFile {
    public static void main(String[] args) throws Exception {
        Map<Integer, String> data = new HashMap<Integer, String>();
        data.put(1, "hello");
        data.put(2, "world");
        System.out.println(data.toString());
        store(data);
        data = (Map<Integer, String>) load();
        System.out.println(data.toString());
    }
    
    public static Object load() throws Exception {
        FileInputStream fileInputStream = new FileInputStream("object.txt");
        ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
        return objectInputStream.readObject();
    }
    
    public static void store(Object data) throws Exception {
        FileOutputStream fileOutputStream = new FileOutputStream("object.txt");
        ObjectOutputStream outputStream = new ObjectOutputStream(fileOutputStream);
        outputStream.writeObject(data);
        outputStream.close();
    }
}

Java Convert File Into Bytes (Array of Bytes)

package com.pritom.kumar;

import java.io.File;
import java.io.FileInputStream;

/**
 * Created by pritom on 28/06/2016.
 */
public class ReadFileAsByteArray {
    public static void main (String[] args) throws Exception {
        File file = new File("x1.zip");

        FileInputStream fileInputStream = new FileInputStream(file);
        byte[] toByte = new byte[(int) file.length()];
        fileInputStream.read(toByte);
        fileInputStream.close();

        System.out.println("File_Length=" + file.length() + ", Byte_Length=" + toByte.length + ", Both_Are_Equal=" + (file.length() == toByte.length ? "True" : "False"));
    }
}

Output:

File_Length=14805774, Byte_Length=14805774, Both_Are_Equal=True

Convert A String (like testing123) To Binary In Java

The usual way is to use String#getBytes() to get the underlying bytes and then present those bytes in some other form (hex, binary whatever).

Note that getBytes() uses the default charset, so if you want the string converted to some specific character encoding, you should use getBytes(String encoding) instead, but many times (esp when dealing with ASCII) getBytes() is enough (and has the advantage of not throwing a checked exception).

For specific conversion to binary, here is an example:

  String s = "foo";
  byte[] bytes = s.getBytes();
  StringBuilder binary = new StringBuilder();
  for (byte b : bytes) {
     int val = b;
     for (int i = 0; i < 8; i++)
     {
        binary.append((val & 128) == 0 ? 0 : 1);
        val <<= 1;
     }
     binary.append(' ');
  }
  System.out.println("'" + s + "' to binary: " + binary);

Running this example will yield:

'foo' to binary: 01100110 01101111 01101111

http://stackoverflow.com/questions/917163/convert-a-string-like-testing123-to-binary-in-java