Thursday, April 17, 2014

How to enable MySQL query monitoring

Do you need to monitor any SQL statements passing through your MySQL server? You would need to turn on the server logging. Edit your my.cnf file and add these:


You also need to restart the database server after these changes.

Wednesday, April 16, 2014

Be careful with Java Path.endsWith(String) usage

If you need to compare the object, be aware that Path.endsWith(String) will ONLY match another sub-element of Path object in your original path, not the path name string portion! If you want to match the string name portion, you would need to call the Path.toString() first. For example

// Match all jar files.
Files.walk(dir).forEach(path -> {
if (path.toString().endsWith(".jar"))

With out the "toString()" you will spend many fruitless hours wonder why your program didn't work.

Monday, April 14, 2014

How to disable MySQL case sensitive with table names in queries

My latest install of MySQL 5.16 on Windows 7 is case sensitive with table names. I much prefer it's case in-sensitive for faster typing and adhoc queries. To do that, I need to edit the my.cnf file (Try running "mysql --help" and it will tell you where it is.)

At the end of the file, add this line:

lower_case_table_names = 1

Tuesday, April 8, 2014

How to setup remote debug with WebLogic Server and Eclipse

Here is how I enable remote debugging with WebLogic Server (11g) and Eclipse IDE. (Actually the java option is for any JVM, just the instruction here is WLS specific.)

1. Edit <my_domain>/bin/ file and add this on top:

JAVA_OPTIONS="$JAVA_OPTIONS -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n"

The suspend=n will start your server without wait for you to connect with IDE. Server usually started with bunch of waiting threads and you can connect with an IDE any any time. You then try to place a break point and fetch a new HTTP request etc to initiate a thread to go into the code breakponit. If you don't want the WLS to wait before fully started, then set it to suspend=y instead.

2. Start/restart your WLS with <my_domain>/bin/

3. Once WLS is running, you may connect to it using Eclipse IDE. Go to Menu: Run > Debug Configuration ... > Remote Java Application and create a new entry. Ensure your port number is matching to what you used above.

Read more java debugging option here:

Now on the IDE Eclipse side, you can connect to your WLS server with the following instruction:

1. In Eclipse menu, select Run > Debug Configuration ...
2. On left side, select Remote Java Application, and then press the + button to create a new configuration.
3. On the right side you can fill in the server info such as hostname and port number.
4. Click Debug button

UPDATE (10/30/14):
Remember each remote debug setup is per JVM and requires a unique port. So how to set each WebLogic Managed Server with unique debug port? You can easily do this by updating your line above to this:

JAVA_OPTIONS="$JAVA_OPTIONS -Xrunjdwp:transport=dt_socket,address=$DEBUG_PORT,server=y,suspend=n" 

Now you can start managed server like this to change the port in a Bash shell by change to your domain directory first, then run:

bash>DEBUG_PORT=8001 bin/ my_server_name

Saturday, April 5, 2014

Creating your own loop structure in Java 8 lambda

Java doesn't have an easy construct of repeat something N number of times. We can make a for loop of course, but many times we don't even care about the variable that we created in the loop. We just want repeat N times of some code and that's it. With the lambda available in Java 8, you may attempt something like this:

public class RepeatDemo {
    public static void main(String[] args) {

        // One liner repeat
        repeat(10, () -> System.out.println("HELLO"));

        // Multi-liners repeat

        repeat(10, () -> {
    static void repeat(int n, Runnable r) {
        for (int i = 0; i < n; i++)

Probably not as eye pleasing or straight forward as the good fashion for-loop, but you do get rid of the unnecessary loop variable. Only if Java 8 would go extra mile and treat the lambda argument in method with sugar syntax, then we could have it something like the Scala/Groovy style, which makes code more smoother. For example:

        // Wouldn't this be nice to have in Java?

        repeat(10) {


Thursday, April 3, 2014

How to reset WebLogic admin server password

If you forgot your admin user password for WebLogic, you can reset it this way. Ensure you are in the domain directory first! 
source $WL_HOME/server/bin/ 
cd mydomain
mv security/DefaultAuthenticatorInit.ldift security/DefaultAuthenticatorInit.ldift.bak
java <admin_username> <new_password> security

Tuesday, April 1, 2014

How to process stream and read text file in Java 8

I have converted one of my old utility class using latest Java8. I use this often to print content of manifest file to check any mysterious jar file for version etc. Just run "java ztools.PrintJar /path/to/my.jar" to see output. In the new code, you will see how I use the Java 8 stream processing to filter what I need from an Enumeration list, and then get the optional result if there is any. And then the BufferedReader now comes with "lines()" method that also do streaming. It's pretty cool to see Java 8 in actions!

package ztools;

import java.util.Optional;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

 * Print text based resource file inside a jar file. (eg: META-INF/MANIFEST.MF)
 * @author Zemian Deng
public class PrintJar {
    public static void main(String[] args) throws Exception {
        // Search given name in a jar
        JarFile jarFile = new JarFile(args[0]);
        final String searchName = (args.length >= 2) ? args[1] : "META-INF/MANIFEST.MF";
        Optional<JarEntry> searchResult = jarFile
                .filter(e -> e.getName().equals(searchName))
        if (!searchResult.isPresent())
            throw new RuntimeException(searchName + " not found!");
        // Print the JarEntry
        JarEntry entry = searchResult.get();
        try (InputStream instream = jarFile.getInputStream(entry)) {
            BufferedReader reader = new BufferedReader(new InputStreamReader(instream));
            reader.lines().forEach(line -> System.out.println(line));