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Recovering from a checked exception in Java

If you are working on the back-end, this might be of use. Very trivial but rarely used. /** * This class demonstrates how to recover from checked exceptions * @author Joset */ public class CheckedExceptionRecovery { /** * @param args the command line arguments */ public static void main(String... args) { InputStreamReader inputStreamReader = new InputStreamReader(System.in); BufferedReader bufferedReader = new BufferedReader(inputStreamReader); int input = 0; boolean done = false; do { try { System.out.println("Please enter an integer: "); input = Integer.parseInt(bufferedReader.readLine().trim()); done = true; } catch (NumberFormatException numberFormatException) { System.out.println("Invalid input. Please try again."); } catch (IOException ioException) { System.out.println("C...
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Controller (MVC) Tips for Java Servlets / JSP

I was inspired by a face-to-face technical interview awhile ago that is why I am writing this down. To avoid having the Servlet’s doXXX() methods clogged, use reflection by breaking down your controller code into modules. Here’s how. You must have the following. 1. Reflection Interface (ServletHandler.java) - An interface for reflection. Nice definition! 2. Main Servlet (MainServlet.java) - A class extending HttpServlet. 3. Module Handler (CreditHandler.java) - A class containing the module’s controller code, for this example, the Credit Module. in file ServletHandler.java , import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public interface ServletHandler { public abstract void setServlet(HttpServlet servlet); public abstract void handle(HttpServletRequest request, HttpServletResponse response); } in file MainServlet.java , protected void doGet(HttpServletRequest r...
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Method Piercing in Java

There’s nothing new here. I just want to reiterate though. class TargetClass { private static String DB_PASSWORD = "sw0rdfish"; private static String getDatabasePassword() { return DB_PASSWORD; } } And the attack? import java.lang.reflect.Method; public class ClassPiercing { public static void main(String... args) throws Exception { Class targetClass = Class.forName("TargetClass"); Method[] methods = targetClass.getDeclaredMethods(); methods[0].setAccessible(true); String databasePassword = (String)methods[0].invoke(null, null); System.out.println("Database Password: " + databasePassword); } } Output: Database Password: sw0rdfish Check out Val’s Blog by clicking [here] . He has more examples.
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Sad reality about Wrapper Classes in Java

Consider the snippet. Integer firstInteger = 1000; // autoboxing Integer secondInteger = 1000; //autoboxing if (firstInteger != secondInteger) { System.out.println("Different objects!"); } if(firstInteger.equals(secondInteger)) { System.out.println("Meaningfully equivalent!"); } Output: Different objects! Meaningfully equivalent! How about this one. Integer firstInteger = 100; // autoboxing Integer secondInteger = 100; //autoboxing if (firstInteger == secondInteger) { System.out.println("Equal objects!"); } if(firstInteger.equals(secondInteger)) { System.out.println("Meaningfully equivalent!"); } And the output? Equal objects! Meaningfully equivalent! And the explanation? Two instances of the wrapper objects will always be == when their primitive values are the same. - Boolean - Byte - Character from \u0000 to \u007F (0 to 127) - Short from -128 to 127 - Integer from -128 to 127 Tsk.
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MD5 Hashing in Java

This is useful for storing passwords in a database though still vulnerable to md5 dictionary attacks, anyway, here’s a static method. public static String hash(String text) { String hashedString = ""; try { MessageDigest md5Hash = MessageDigest.getInstance("MD5"); md5Hash.update(text.getBytes(), 0, text.length()); hashedString = new BigInteger(1, md5Hash.digest()).toString(16); } catch (NoSuchAlgorithmException exception) { exception.printStackTrace(); } return hashedString; } This will return the MD5 hash. Have a great day!
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