Java ReentrantLock example

ReentrantLock and synchronized keyword both can make sure only one thread execute the code on the same time. They are similar but not the same. ReentrantLock is more flexible than synchronized. In this page I will show you a simple use case of ReentrantLock.

Linux scp command examples

scp command can help you copy file from remote computer. Here are some examples.

Linux awk command examples

awk is more power than grep when you want handle the text in Linux. awk read the input line by line and split the words by space. You can also define your own separator.

git merge rebase

There are two ways to put your change to remote: merge and rebase. Let's say there is a branch and you develop your feature in this branch. You merge the changes to this branch you will get the result like following.

Git create remote branch

You can use these commands to create a new branch locally and push it to remote.

mysqldump access denied when doing LOCK TABLES

When I try to dump the table with the mysqldump command I got the error message. The dump command and the error message are here.

Java8 convert list to map

Before Java8 if you need convert list to map you have to iterate over the list. Java8 provide stream to help you iterate over the list. You can convert list to map by using stream with only one line of code.

Spring Data keyvalue example

Spring Data KeyValue framework use java.util.Map to store data in memory. I will show you how use it in this page.

Java isAssignableFrom example

The isAssignableFrom method is used to judge the relationship of two classes. This method can tell you whether A is the subclass of B. or A class implement B interface. The example code is here.

Java finally example

The code in finally block will always be executed except invoke System.exit() method. The example code is like following.

Spring data jpa example

This is a sample example to quick start to use spring data framework. I assume you have created a Mysql database which name is db. For quick start we only save data into database and query them out without any condition.

Book list

So many books, so little time.

Java force garbage collection

As we all know, JVM will do garbage collection when there is not enough memory to use. You can use System.gc() in your code to trigger garbage collection. But when JVM does this is not uncertainty.

spring boot handlerexceptionresolver example

There are many ways to handle the exception in Spring Boot. You can click Spring Boot exception handler example or Spring Boot global exception example to see how to handle exception in controller or handler. I will show you how to handle exception by implementing HandlerExceptionResolver.

Java add separator to string

Let's say you have a list of string and you want to add separator to them. If you use JDK8+ you can use String.join(). For JDK7-, I recommend you to use StringUtils in apache-commons-lang. The code is like following.