Java coding notes II

1. 1. Print all properties of an Object with name/value
2. 2. Compare two objects
3. 3. URL encoding of query string parameter
4. 4. Base64 data encoding | decoding
5. 5. Scrambling a string (scrambled email)
6. 6. A simple way to swap values
7. 7. Convert String[] to List<String>
8. 8. Null-safe comparator

• Print all properties of an Object with name/value

public void printObjectFields(Object object) {
        Field[] fields = object.getClass().getDeclaredFields();
        StringBuilder msg = new StringBuilder();
        String newLine = System.getProperty("line.separator");

        msg.append( object.getClass().getName() );
        msg.append(newLine);
        Method method = null;
        String methodName = "";
        String methodValue = "";
        for ( Field field : fields ) {
            msg.append("  ");
            try {
                methodName = field.getName();
                msg.append( methodName );
                msg.append(": ");
                //requires access to private field:
                //field.setAccessible(true);
                
                //run the `get` method to obtain the value
                methodName = "get" + Character.toUpperCase(methodName.charAt(0)) + methodName.substring(1);
                method = object.getClass().getMethod(methodName);
                methodValue = String.valueOf(method.invoke(object));
                msg.append(methodValue);
            } catch (SecurityException e) {
            } catch (NoSuchMethodException e) {
            } catch ( IllegalAccessException e ) {
            } catch (IllegalArgumentException e) {
            } catch (InvocationTargetException e) {
            }
            msg.append(newLine);
        }
        //print msg
    }

• Compare two objects

Compare every filed of two objects by using CompareToBuilder…

private int compareBrand(Brand oldBrand, Brand newBrand) {
    return new CompareToBuilder().append(oldBrand.getBrandId(), newBrand.getBrandId())
            .append(oldBrand.getBrandName(), newBrand.getBrandName())
            .toComparison();
}

• URL encoding of query string parameter

Either using java.net.URLEncoder:

String str = "a=b+c";
str = URLEncoder.encode(str, "UTF-8");

OR using Regex:

String str = "a=b+c";
str = str.replaceAll("\\+", "%2B").replaceAll("\\=", "%3D");

Useful link: What every web developer must know about URL encoding

• Base64 data encoding | decoding

import java.util.Base64;
String str = "abcde"
byte[] bytes = str.getBytes("UTF-8");
String encoded = Base64.getEncoder().encodeToString(bytes);
byte[] decoded = Base64.getDecoder().decode(encoded);
strDecoded - new String(decoded);

• Scrambling a string (scrambled email)

Recently, I need a method to generate a fake email address with existing user email…

1. Scramble a input string by shuffling all charaters with equal probablities
2. Scrambling by appending some random letters and numbers
3. First character should be a letter

Here is the code:

public static String scrambleString(Random random, String str)
{
    //convert string to a char array
    char charArray[] = str.toCharArray();
    //random alpha and num
    String randAlphaNum = RandomStringUtils.randomAlphanumeric(str.length()).toLowerCase();
    //random first letter
    final String allowedChars = "abcdefghijklmnopqrstuvwxyz";
    char firstChar = allowedChars.charAt(random.nextInt(allowedChars.length()-1));
    // Scramble the letters with equal probabilities
    for( int i = 0; i < charArray.length - 1; i++ )
    {
        // Choose a random num from remaining numbers
        int j = random.nextInt(charArray.length - 1 - i) + i;
        // Swap letters
        char temp = charArray[i];
        charArray[i] = charArray[j];
        charArray[j] = temp;
    }
    return firstChar + new String(charArray) + randAlphaNum;
}

• A simple way to swap values

int swap(int a, int b) {    
  return a;
}

//when usage  
b = swap(a, a=b);

This method is a bit tricky. It relies on the fact that a will pass into swap() before b is assigned to a. Then, b is returned and assigned to a.

This method can be generic and swap any number of objects of the same type:

int swap(int a, int b, int c) {    
  return a;
}

//usage
c = swap(a, a=b, b=c)

• Convert String[] to List<String>

In order to use some util method like add(), remove(), contains()…

List<String> newCurrencies = new ArrayList(Arrays.asList(currencies));
List<String> oldCurrencies = new ArrayList();

Note: If initializing it in the following way, the size of newCurrencies will be fixed, so it cannot use some of the util methods.
E.g. List<String> newCurrencies = Arrays.asList(currencies);

• Null-safe comparator

It’s case-insensitive with assumption of emptyString == null.

public static int nullSafeStringComparator(final Object str1, final Object str2) {
    if (str1 == null ^ str2 == null) {
        //particularly, we consider null == emptyString
        if (String.valueOf(str1).trim().isEmpty() || String.valueOf(str2).trim().isEmpty())
            return 0;
        return (str1 == null) ? -1 : 1;
    }
    if (str1 == null && str2 == null)
        return 0;
    //since neither one is NULL here, toString() works
    return str1.toString().compareToIgnoreCase(str2.toString());
}

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