How to convert a String array to a Byte array? (java)

Array to Array you should convert manually with parsing into both sides, but if you have just a String you can String.getBytes() and new String(byte[] data); like this

public static void main(String[] args) {
    String[] strings = new String[]{"first", "second"};
    System.out.println(Arrays.toString(strings));
    byte[][] byteStrings = convertToBytes(strings);
    strings = convertToStrings(byteStrings);
    System.out.println(Arrays.toString(strings));

}

private static String[] convertToStrings(byte[][] byteStrings) {
    String[] data = new String[byteStrings.length];
    for (int i = 0; i < byteStrings.length; i++) {
        data[i] = new String(byteStrings[i], Charset.defaultCharset());

    }
    return data;
}


private static byte[][] convertToBytes(String[] strings) {
    byte[][] data = new byte[strings.length][];
    for (int i = 0; i < strings.length; i++) {
        String string = strings[i];
        data[i] = string.getBytes(Charset.defaultCharset()); // you can chose charset
    }
    return data;
}

for one byte[] from string[] you have to:

• to byteArray concat byte arrays from each string using some delimeter
• from bytearray split by te same delimiter and create String as I described above.

String.getBytes()? is what you're looking for.

You can iterate for each string and keep appending to the final byte array.String example = "This is an example"; //Convert String to byte[] using .getBytes() function byte[] bytes = example.getBytes(); //Convert byte[] to String using new String(byte[])
String s = new String(bytes);

You don't say what you want to do with the bytes (aside from convert them back to a String[] afterward), but assuming you can just treat them as an opaque bag of data (so you can save them to a file or send them over the network or whatnot, but you don't need to examine or modify them in any way), I think your best bet is to use serialization. To serialize your string-array, you would write something like:

final String[] stringArray = { "foo", "bar", "baz" };

final ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
final ObjectOutputStream objectOutputStream =
    new ObjectOutputStream(byteArrayOutputStream);
objectOutputStream.writeObject(stringArray);
objectOutputStream.flush();
objectOutputStream.close();

final byte[] byteArray = byteArrayOutputStream.toByteArray();

and to recover it afterward, you'd write the reverse:

final ByteArrayInputStream byteArrayInputStream =
    new ByteArrayInputStream(byteArray);
final ObjectInputStream objectInputStream =
    new ObjectInputStream(byteArrayInputStream);

final String[] stringArray2 = (String[]) objectInputStream.readObject();

objectInputStream.close();

I would treat this as a serialization problem and just implemented it as follows(complete and working Java code):

import java.nio.ByteBuffer;
import java.util.ArrayList;

public class Serialization {
    public static byte[] serialize(String[] strs) {
        ArrayList<Byte> byteList = new ArrayList<Byte>();
        for (String str: strs) {
            int len = str.getBytes().length;
            ByteBuffer bb = ByteBuffer.allocate(4);
            bb.putInt(len);
            byte[] lenArray = bb.array();
            for (byte b: lenArray) {
                byteList.add(b);
            }
            byte[] strArray = str.getBytes();
            for (byte b: strArray) {
                byteList.add(b);
            }
        }
        byte[] result = new byte[byteList.size()];
        for (int i=0; i<byteList.size(); i++) {
            result[i] = byteList.get(i);
        }
        return result;
    }

    public static String[] unserialize(byte[] bytes) {
        ArrayList<String> strList = new ArrayList<String>();
        for (int i=0; i< bytes.length;) {
            byte[] lenArray = new byte[4];
            for (int j=i; j<i+4; j++) {
                lenArray[j-i] = bytes[j];
            }
            ByteBuffer wrapped = ByteBuffer.wrap(lenArray);
            int len = wrapped.getInt();
            byte[] strArray = new byte[len];
            for (int k=i+4; k<i+4+len; k++) {
                strArray[k-i-4] = bytes[k];
            }
            strList.add(new String(strArray));
            i += 4+len;
        }
        return strList.toArray(new String[strList.size()]);
    }

    public static void main(String[] args) {
        String[] input = {"This is","a serialization problem;","string concatenation will do as well","in some cases."};
        byte[] byteArray = serialize(input);
        String[] output = unserialize(byteArray);
        for (String str: output) {
            System.out.println(str);
        }
    }
}

The idea is that in the resulting byte array we store the length of the first string(which is always 4 bytes if we use the type int), followed by the bytes of the first string(whose length can be read later from the preceding 4 bytes), then followed by the length of the second string and the bytes of the second string, and so on. This way, the string array can be recovered easily from the resulting byte array, as demonstrated by the code above. And this serialization approach can handle any situation.

And the code can be much simpler if we make an assumption to the input string array:

public class Concatenation {
    public static byte[] concatenate(String[] strs) {
        StringBuilder sb = new StringBuilder();
        for (int i=0; i<strs.length; i++) {
            sb.append(strs[i]);
            if (i != strs.length-1) {
                sb.append("*.*"); //concatenate by this splitter
            }
        }
        return sb.toString().getBytes();
    }

    public static String[] split(byte[] bytes) {
        String entire = new String(bytes);
        return entire.split("\\*\\.\\*");
    }

    public static void main(String[] args) {
        String[] input = {"This is","a serialization problem;","string concatenation will do as well","in some cases."};
        byte[] byteArray = concatenate(input);
        String[] output = split(byteArray);
        for (String str: output) {
            System.out.println(str);
        }
    }
}

The assumption is that *.* does not exist in any string from the input array. In other words, if you know in advance some special sequence of symbols won't appear in any string of the input array, you may use that sequence as the splitter.