recent posts related to java, jdbc, spring, etc.

Java 10: How to implement About, Preferences, and Quit menu items on MacOS alvin June 2, 2018 - 5:20pm

If you want to implement About, Preferences, and Quit handlers with Java 9 and newer on MacOS systems, this example Java source code shows how to do it:

A Java Factory Pattern example

Java Design Patterns FAQ: Can you provide an example of the Factory Pattern in Java?

Sure. In this article we'll look at a small-but-complete example of the Factory Pattern ("Factory Design Pattern") implemented in Java.

How to speed up JDBC PreparedStatement MySQL batch inserts

If you ever need to batch-insert a lot of records into a MySQL/MariaDB database using the JDBC PreparedStatement (as in preparedStatement.executeBatch()) be sure to change the MySQL URL to use the rewriteBatchedStatements, as shown here:


For a recent project I needed to batch-insert about eleven million records into a MySQL database, and the runtime was about 55 minutes. Once I added rewriteBatchedStatements=true to the MySQL URL, the batch-insert time was reduced down to only three minutes. That one little change made all the difference.

A Java method to round a float value to the nearest one-half value

As a quick note, here’s a Java method that will round a float to the nearest half value, such as 1.0, 1.5, 2.0, 2.5, etc.:

 * converts as follows:
 * 1.1  -> 1.0
 * 1.3  -> 1.5
 * 2.1  -> 2.0
 * 2.25 -> 2.5
public static float roundToHalf(float f) {
    return Math.round(f * 2) / 2.0f;

The comments show how this function converts the example float values to their nearest half value, so I won’t add any more details here. I don’t remember the origin of this algorithm — I just found it in some old code, thought it was clever, and thought I’d share it here.

JavaFX is going to be removed from the Java JDK

Just read that JavaFX is going to be removed from the Java JDK. From the article: “Making JavaFX its own module will make it easier to adopt and clear the way for new contributors, Oracle said. The company added that with the faster release schedule being implemented for standard Java and the JDK, JavaFX needs to be on its own pace driven by contributions from Oracle and others in the OpenJFX community.”

The keytool password for the Java security cacerts file is ... alvin January 22, 2018 - 8:12pm

In case you ever need to manually a certificate to your ${JAVA_HOME}/jre/lib/security/cacerts file, it turns out the password for that file when using the Java keytool command is changeit.

To add a certificate to that file, you’ll want to use a command like this:

keytool \
    -import \
    -alias "" \
    -keystore ${JAVA_HOME}/jre/lib/security/cacerts \

I had to do this today for a Java/Scala script that accesses an HTTPS URL, and the site I’m accessing uses a “Let’s Encrypt” certificate.

How to create a “spacer” in JavaFX (with a Region)

As a brief note to self, I just created a “spacer” in JavaFX using a Region, as shown in this code:

// a spacer to push the visible elements up a little
val spacer = new Region
VBox.setVgrow(spacer, Priority.ALWAYS)

I originally created the spacer as a Separator, which is the wrong thing (it’s more like an HTML <hr> tag). A JavaFX Region just gives you a blank space, which you can control as needed.