Posts in the “java” category

Java FAQ: Can you share some source code for a “Java wget” program, i.e., a Java program that works like the Unix wget or curl commands?

Here's the source for a program I've named JGet, which acts similar to the wget or curl programs. I didn't have wget installed when I needed it (and my client wouldn't let me install it), so I wrote this Java wget replacement program.

As a quick note, if you need some examples of the syntax of how to write a Java method that returns a generic type, I hope these are helpful:

public static <T> T getRandomValue(List<T> listOfPossibleOutcomes, int numPossibilities) {
    int r = RandomNumberGenerator.getRandIntBetween(0, numPossibilities);
    return listOfPossibleOutcomes.get(r);
}

public static <T> T getRandomValueFromGenericList(List<T> list) {
    Collections.shuffle(list);
    return list.get(0);
}

I hadn’t written a Java generic method in a while, and I forgot you need to declare the generic type (<T>) early in the method declaration.

In an earlier Java Properties file example I showed how to load a Java Properties file and then access the elements in the Properties object, but for today, if you just need a method to read a Java Properties file, I hope the following source code will be helpful to you:

Java directory FAQ: "How do I delete a directory tree in Java?"

Java delete directory - discussion

The delete method of the File class won't delete a directory tree, meaning that in the old days you had to write your own recursive method to do this.

I've been thinking about rewriting my old tutorial on how to execute system processes from a Java application for a while now (How to run system commands from Java applications), but it's a topic that quickly becomes complicated if you want to do it right, so I kept postponing it until I could give it some quality time in a real-world project.

In earlier articles I've described how to execute system commands from Java applications. A long time ago I wrote my first article on this topic (How to execute system commands from Java), and more recently I wrote an updated version of that article titled "Executing system commands from Java using the ProcessBuilder and Process classes".

Java Date FAQ: How do I determine tomorrow's date in Java?

Many times when you're working with a Java Date, you need to be able to add something to a date, i.e., to get tomorrow's date, or the next week, or the next year. In this short tutorial, we'll demonstrate how to easily add one day to today to get tomorrow's date.

Summary: This article shares some source code for a Java socket debugging method.

I'm not going to describe this much today, but here's the source code for a Java class I put together from a number of other sources on the internet. In short, this code uses a Java Socket to connect to a port on a remote server, sends a command to that server to be executed, and then reads the output from the command that is executed. As a result, I assume that all information sent is text (nothing binary).

Problem: In a Java program, you want to determine whether a String contains a pattern, and you'd rather use the String matches method than use the Pattern and Matcher classes.

Question: How do I convert a String to a long with Java?

Answer: The Long class includes a method named parseLong() that serves just this purpose. An example of a simple program that performs this conversion is shown below:

I don’t know where this originated, but I just saw it on a friend’s Facebook feed. Nothing like Java humor. :)

Java keytool FAQ: Can you share an example of how to use the Java keytool command to create and share a Java/keytool certificate?

Here's a quick look at how two people, John and Paul, might use the Java keytool command to create and share a certificate file. In this example, John will create the certificate with the "keytool genkey" and "keytool export" commands, and Paul will import John's public key from the certificate file with the "keytool import" command.

Java FAQ: Can you show me an example of the Java 5 for loop syntax? (Java 5 and newer)

Answer: Sure. I've created a sample Java program to demonstrate the Java 5 for-each loop syntax, using both a List with pre-Java5 syntax, and a second example using Java 5 generics syntax.

Java 5 for loop syntax example

Without any further ado, here is the example code:

I was just digging around through a Java FTP program I wrote, and found the following class, which might be a nice reference for other people. This class lists all the possible FTP server return codes (status codes) that your Java FTP program can receive in return to a call to an FTP server.

I've been doing a lot of work with Java and images on Mac OS X lately, and I thought I'd share a Java method I use to get an image off the clipboard. I won't get into the details of working with an Image or a BufferedImage in this tutorial, but I will show you how to get the Image off the clipboard.

Java MySQL FAQ: Can you share an example of a Java MySQL UPDATE example (using a Java PreparedStatement object)?

Java MySQL INSERT example: Can you share an example of a Java MySQL INSERT example using the Java Statement class?

Summary: A Java MySQL DELETE example, demonstrating how to issue a SQL DELETE command from your Java source code.

Today was mostly a day off for me, but I thought I'd do one thing here to help organize the website a little better. To that end, I've put together a list of the Java MySQL examples I've created, i.e., Java database examples that were specifically written for MySQL.