Frequently there is a need to logon to a remote system and run some commands or programs to get the output, many software can serve this purpose such as putty and gitshell.These software usually provide secure access to the remote system. But have you ever wondered what to do if you need to run commands on many different systems at the same time and get all these results back at a single place? Especially in big data era, many tasks may run on different distributed systems and you want o have a single place to accumulate the result.In this post, we will introduce a Java library which can help ...

JKS is Java Keystore, a proprietary keystore type designed for Java. It can be used to store private keys and certificates used for SSL communication, it cannot store secret keys however. The keytool shipped with JDKs cannot extract private keys stored on JKS. This type of keystore usually has an extension of jks.Next we will show how to operate the JKS keystore with pure Java code.Create JKS keystoreThe simplest method to create a JKS keystore to create an empty keystore. We can first get an instance of KeyStore and then load a null keystore. After loading the null keystore, we just need to c...

What is the difference between Hacking and programming? One opinion I have heard expressed is that a hacker can put a lot of code together in a hurry but if a change is needed the code has to be completely rewritten. A programmer may take a little longer but if changes are needed they are more quickly and easily installed without the need for a complete rewrite. One source I heard attributed an observation like this to Maggie Johnson of Google. It rings true to me though. Hacking is usually described as “quick and dirty.” You though a bunch of code together and make it up as you go...

As a IT professional, we often need to capture screenshot of what we are working on to give proof of what we are doing and why we do it. The screenshot will provide a good sense to other people. You may be familiar with taking screenshot with different tools such as snagit, snipping tool or the Windows PrtSc button. But do you know how to take a screenshot of a dropdown menu?Here we show you how to capture screeenshot of dropdown menu with the snipping tool provided since Windows 7. Below are the steps:1. Open snipping tool and press Esc2. Move to the dropdown menu and expand it3. Then press C...

A .htaccess file is a directory-level configuration file supported by several web servers, that allows for decentralized management of web server configuration. What can a .htaccess file do? We summarized some of them here.  Hope it may help you. 1. Timezone settingSometimes when you use date() or mktime() functions in PHP, , it may display some weird information because of the timezone difference. For example, one possible warning is :Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone...

Following my article A String is not an Error, I want to bring attention to an issue that similarly applies to JavaScript in general, but has special relevance in the Node.JS environment.The problem boils down to the usage of {} as a data-structure where the keys are supplied by untrusted user input, and the mechanisms that are normally used to assert whether a key exists.Consider the example of a simple blog created with Express. We decide to store blog posts in memory in a {}, indexed by the blog post slug. For example, this blog post would be posts['an-object-is-not-a-hash'].We start writin...

In previous post, we have introduced the use of Certificate and how to generate self signed certificate using Java. In this post, we will show you how to generate a certificate chain. Sometimes we may only have a certificate request or we don't have a trusted certificate which can be used for business. Now we need to have a trusted CA to sign our certificate so that it can be used on SSL communications.To generate a certificate chain, we may first have our own certificate(A), then we may use other certificate(B) and its associated private key to sign the certificate we have, then we will use a...

Both ConcurrentHashMap and Hashtable are Collection classes for storing key value pairs and they both provide fast element search with a supplied key. They have much in common. However, we will not discuss the similarities between them here, instead we will focus on the differences between them.ConcurrentHashMap and Hashtable are both thread safe. But the mechanism for thread safe is different between them. Hashtable is synchronized, it utilizes the synchronization mechanism; while ConcurrentHashMap uses segmentation to lock the data, it uses concurrent locks operations for thread safety inste...