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.
SimpleDateFormat is the only choice when you want to parse String to Date before Java8. But, SimpleDateFormat is unthread-safe class. You may get the wrong result when you use it in multi-thread scenario. I recommend you use DateTimeFormatter to handle date string.
There are two ways to convert LocalDateTime to Date in java. Both of them need convert LocalDateTime to Instant then convert Instant to Date. LocalDateTime and Instant are new classes in Java8 I recommend you to use them instead of Date. Here is the sample code.
Don't use SimpleDateFormat in multi-threaded scenario. It is not thread-safe class. Here is the code to verify it. I start 10 threads to parse string to date with the same instance of SimpleDateFormat.
spring-boot-maven-plugin can help you build runnable Spring Boot jar. Add following config in your pom file and execute clean install you will get a runnable jar file.
In this page I will show you how to use gson parse json string to object array. Add gson dependency in pom.xml file.
We can use stream().parallel() to handle tasks in multi-thread. CompletableFuture is very useful when you handle tasks which need to wait IO or network. Let's say you have two services. The one is getting content by contentId and another is getting author information by authorId. Both of them need RPC. In other words, you have to wait the remote server responses. I use Thread.sleep() to mock network delays.
We can use Arrays.asList() to init an array with values. This page will show you how to convert List
You may have used ThreadPoolExecutor to submit some task and waiting for the result. In this way program can get the better performance. The question is how to calculate the size of pool size, in other words how to make CPU 100% or close to 100% busy?
Stream in Java8 can help us make code clear and efficient. We can use Stream to iterate a collection without the keyword for. It is very convenient. The question is how to print the information of item in a stream? In this page I will show you how to add log in stream. JDK provides peek function for debugging.
In this page I will show you how to integrate MyBatis and Spring. I use maven to build the project. The structure of the project is like following.
We can use show create table
There are different ways to generate random 6 digits. I recommend you to use RandomUtils or RandomStringUtils in apache-common-lang3 framework to generate it. Here is the sample code.