Need to convert an integer to an enum in Java? The bad news is that it is not as easy as it should be, but the good news is that it is still easy! Consider the enum below. public enum PageType { ABOUT(1), CODING(2), DATABASES(3); private int value; private static Map map = new HashMap();… read more
In this article, we will take a look at how we can replace newline characters in Java. Additionally, we will implement a custom JSTL tag so that we can replace newline characters with corresponding <br /> break lines within JSP files. Unlike PHP’s nl2br function, for instance, this is not as easy in JSTL. Replacing… read more
Generating a UUID in Java is extremely easy. In fact, it can be done with a single line of code! To generate a type 4 UUID in Java, simply run the following line of code. String uuid = UUID.randomUUID().toString(); // Example: e03913fb-5951-4964-a88b-47371641fd17 Because you will likely generate UUIDs in many different contexts, here is a… read more
Please note that the following code examples exclusively use Java’s validation API, so these examples are in no way limited to Hibernate Validator. Hibernate Validator is merely used as the implementation of the used interfaces, but other implementations can be used as well. Validating a single field with Hibernate Validator is easy. Suppose that you have… read more
Generating a CRC32 checksum in Java is – as you would expect – extremely simple. All it takes is a few lines of code. Below is an example on how to generate a CRC32 checksum from a string. public final class AppUtils { private AppUtils() { } public static long crc32(String input) { byte[] bytes… read more
If you have a column in your database which may only contain the value 0 or 1 (i.e. a bit value), you probably want to map it to the boolean static type in your entity, rather than an integer. This could be the case for smallint, tinyint(1), int(1), boolean columns, etc. I found two suggestions… read more
Did you know that you can return a boolean value from a Spring Data JPA query? For instance, you may want to know whether or not an entity (i.e. database row) exists with a given value for a field. Surely one could simply return the row count and check if it is larger than zero, but… read more
With object-relational mapping (ORM) tools such as Hibernate, one usually modifies entities by first fetching them from the database, modifying some fields, and then persisting the entities again. This is a good approach in many cases, but in some scenarios this may not be desirable. For instance, if you want to update a collection of entities (i.e.… read more
I recently had a problem with one of my Spring Data JPA queries; for some reason, I was getting the following exception. query specified join fetching, but the owner of the fetched association was not present in the select list This seemed strange, because I had written a standard JPQL/HQL query that I knew worked.… read more
In order to share session cookies between subdomains in your Java web application hosted with Apache Tomcat, you need to make a simple configuration change. What you simply need to do is to make a small change to your web application’s context. You might have more than one context if you have more than one… read more