Generally we call methods in a synchronous manner. In some cases we need to call methods asynchronously. @Async can help us call methods asynchronously when using Spring Boot. Before using @Async we need to add an @EnableAsync on the startup class. Here's a simple example that shows how to use @Async to implement asynchronous method calls.
Recently I am writing a program that processes messages in the background. The program quits when I start 10 threads. I checked all the exception stack information and found no errors. I tried to find this "error" on Google and didn't find any useful information. Why my program or my thread stop? I read my code line by line. It seems like following.
The default data directory of MySQL is /var/lib/mysql. If there is no disk space for this directory we need to move data to another directory(another fileSystem). In my environment I install MySQL by yum command. The /var/lib/mysql directory is mounted on / and there is no more space for data. I change data directory by using these following commands.
fastjson is excellent framework for handle json data. It can parse json string to generic classes. Here is sample code.
We can use telnet to check weather the remote server port is open or not. The command is easy to use, just telnet
Sometimes we need copy file from server to local. There are several ways to do that. We can use scp, sz commands to transfer files. scp command need us to input local IP, username and password. sz command need us to install lrzsz. Today I found another way to do this.
The class StopWatch class which in apache-common-lang package is a good tool for timing. It provides some useful method to measured running time of program. Most of these methods of StopWatch are easy to understand. Only one method: split() need us try to understand.
When I defined thrift file I need to create a column of numbers. The file looks something like this.
In this page I will show you how to use RSA to encrypt and decrypt data. As we all know RSA is one of asymmetric cryptographic algorithm. We need generate public key and private key before encrypting and decrypting data. The sample code is here.
We can use Jackson convert between json and object. But sometimes we need custom deserializer for special json. Let's say you need to handle the json like following.
Git is a distributed revision-control system.
Java Microbenchmark Harness is a good tool to test your code. It can tell you the code is efficiently or not. Today I will show you how to use it to test your code. Let's say you want to implement a functionality about probability. Maybe you want your program have a 1/10 probability of doing something. You have two ways to implement this.
Let's say you have installed some packages in your Linux. The following commend help you show installed packages. Use yum and grep commends can help you find installed packages.
In MySQL we can add \G in the end of sql to show the result vertically. In PostgreSQL you need to enter \x to show the result vertically. It is a toggle. Example sql is here.
In this book Systems Performance: Enterprise and the Cloud author make a single CPU cycle equivalent to one second to make us feel how fast CPU is.