When maintaining code using version control systems such as git, it is unavoidable that we need to rollback some wrong commits either due to bugs or temp code revert. In this case, rookie developers would be very nervous because they may get lost on what they should do to rollback their changes without affecting others, but to veteran developers, this is their routine work and they can show you different ways of doing that.In this post, we will introduce two major ones used frequently by developers.git resetgit revertWhat are their differences and corresponding use cases? We will discuss them ...

PKCS12 is an active file format for storing cryptography objects as a single file. It can be used to store secret key, private key and certificate.It is a standardized format published by RSA Laboratories which means it can be used not only in Java but also in other libraries in C, C++ or C# etc. This file format is frequently used to import and export entries from or to other keystore types.Next we will explain the operations which can be performed on PKCS12 keystore.Create PKCS12 keystoreBefore storing an entry into a PKCS12 keystore, the keystore has to be loaded first. This means we have t...

In this post, I will create a HTTPS server and HTTPS client demo which can establish HTTPS communication between a server and a client using Java. This should be very useful when we want to test our understanding about SSL communication. We will use both a detailed SSL client and a simple HttpsURLConnection as the HTTPS client.Before creating the actual HTTPS server and HTTPS client, we first need to generate the keystore and truststore to be used by the server and client. To generate the keystore, we can follow instructions at Different types of keystore in Java -- JKS. In this demo, we ...

Do you know what value will be printed when following program is ran?class Test { public int aaa() { int x = 1; try { return ++x; } catch (Exception e) { } finally { ++x; } return x; } public static void main(String[] args) { Test t = new Test(); int y = t.aaa(); System.out.println(y); }}And before answering the above question, do you have answers to following questions?If there is a return statement in try block, will the finally block be executed when the return is executed?If finally will be exe...

ConcurrentHashMap and Collections.synchronizedMap() both provide thread-safe operations of collections of data. They are used in multithreaded programs to provide both thread safety and performance improvements. In many cases, we can use either of them.But the realization of thread safety is different for these two implementations. ConcurrentHashMap will create an HashEntry[] array internally to store the elements passed in from a Map, while Collections.synchronizedMap() will return a SynchronizedMap.The main difference between these two is that ConcurrentHashMap will lock only portion of the ...

Socket is a kind of interface for different sides t communicate, it usually identified by an IP and a port. There are many server side software on a server and they would provide different service. Each server many create some sockets and bind them to some ports so that clients can listen to.Software on the Internet will exchange data though a bidirectional connection established. Each end of the connection has a socket created. In Java, Socket and ServerSocket are in java.net package, ServerSocket is used for server side and Socket is used when establishing connection. Once a successful conne...

You may notice that there is no max/min function provided to compare the maximum/minimum of two or more integers if you are a GoLang developer with some experience . In other languages, these functions are provided as part of the core lib functions. Have you wondered why? Indeed GoLang provides max/min function in math package, but they are used for comparing float64 data type. The signature of these two functions aremath.Min(float64, float64) float64math.Max(float64, float64) float64The reason why GoLang provides the max/min function for comparing float64 numbers are that floating n...

I got an email request to publish this article a few days ago.I was actually on the verge of moving the email to the trash when I noticed the first name of the author: Rand.For those of you not familiar with the Wheel of Time series, the main character’s name is Rand.I admit that it’s an embarrassing weak reason to respond to a strange email, but reading some 10,000 pages of a fantasy series obviously messes with your mind.Then again, it’s probably no stranger than Rand Mendoza wanting to publish his article on this blog to begin with.Anyways, enjoy…**...