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Posts Tagged ‘java’

How to Print out Http Request Headers in Java Servlet

August 25th, 2015 1 comment

While developing a new project, I need to check a request header from client side AJAX call in Javascript. This is not a difficult problem at all, but I found it’s pretty helpful with the headers printed in the log file, especially while debugging. The following code snippet iterates through all the headers and add their values into the string buffer, and further into logger of the Servlet. Notice that the value of a header is not a primitive value, therefore the inner loop is needed to go over each element.

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How to Pretty Print JSON with Gson and Jackson

May 20th, 2015 No comments

In my last article, I compared two leading JSON APIs in Java: Jackson and Gson. If you have tried the samples there, you may have noticed that the two samples print the JSON string into one line. While it’s pretty efficient for machine, it may not easy for human consumption when the Json string is long. Sometimes I have to copy a long Json string into an editor to find out what are there.

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Tricks and Tips on Paypal Integration

April 24th, 2015 1 comment

After releasing the DoubleClou ICE, I finally got some time to write what I had experienced with Paypal as a user and developer. Because the DoubleCloud ICE is productivity tool that sells within $100, I want people to buy it online quickly and easily. Given Paypal’s #1 position in online payment, I turned to Paypal without much thinking. After that I had gone through all the integration process from initial research to bring the site to production.

Gson vs Jackson: Which to Use for JSON in Java

March 27th, 2015 7 comments

There are many JSON libraries for Java. While it’s nice to have many options, it can also be frustrating to decide which one to use. If you do an online search, you will find many opinions and all these libraries are used somewhere. When in doubt, the best thing to do is: stop searching and start coding. It doesn’t take long to get the ultimate answer for you.

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Rotating Log Files with Logback

November 25th, 2014 1 comment

Just fixed an issue related to configuration of Logback recently. You may be wondering why the Logback is used given that it’s much less known than Log4j and Java Logging. Very good question. This page from Logback may provide you some insights. I haven’t tested the performance, but it’s said to be 10 times faster than others. There is also an independent version of comparison on StackOverflow. After browsing it, I didn’t have an impression that I have to use one over the other.

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OAuth For HTTP and REST API Authentication

November 24th, 2014 No comments

Authentication is to verify users are really whom they claim they are. Since its inception, HTTP(s) has used different approaches like BASIC authentication, Form based authentication. Both require passing the user name and password from the client to the server. It’s definitely not good idea to use HTTP because the password is passed as it is or with very limited encoding like BASE64 – very easy to intercept the IP packets and extract out the password. When HTTPs is used, it’s much harder to get the password as all the traffic are encrypted. Still it’s subject to attacks like man-in-the-middle.

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Gradle for Building Java Applications

November 3rd, 2014 1 comment

Building software is a very important part of software development cycle. In the C/C++ age, we used make and continue to use it today. When it came to Java age, two important build tools emerged: Ant and Maven. The former is very similar to make, but instead of script it uses XML. Both make and Ant describe HOW to build software in steps. The Maven takes a quite different approach – it describes WHAT the built software is using XML, and leaves the how to the Maven and its plugins.

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Parsing, Modifying, and Generating Java Source Code With Javaparser

June 24th, 2014 3 comments

It’s not common to do something with Java source code programmatically, but I find the javaparser project is very handy if such a use case comes up. It’s a Java 1.5 parser with AST generation and visitor support. With the API, you can access various elements in the source code like class, methods, statements, javadoc, comments, etc.

Java 8 New Features: JavaFX

May 4th, 2014 2 comments

The JavaFX is not really a new feature, but it’s the first time for it to make into a major Java release. JavaFX has a pretty long history as the next big thing for building cross platform GUI applications. Initially it has its own scripting language and hasn’t made its way in the Java community. The reason is simple: although the JavaFX has richer features on graphics, it does not seem worth learning a new language for it. For a long time, I was wonder why Sun didn’t use the investment to improve its Swing library which has much bigger audience than JavaFX.

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Java 8 New Features: Nashorn JavaScript Engine

April 28th, 2014 No comments

When JavaScript was created, it had not much to do with Java. It’s named as such maybe due to the popularity of Java language at that time. But over the years, JavaScript has gained its own popularity and dominated the client side of Web applications. There are even some work for JavaScript to extend its reach to the server side, for example, Node.js.

Accessing Database in Java with JDO

April 27th, 2014 No comments

I haven’t written Java code to access relational database for a while. Over the years there have been lots of progresses, especially with various Object Relational Mapping (ORM) frameworks. With these frameworks, accessing relational databases becomes pretty easy. In some cases, you don’t have to know SQL at all. Of course understanding SQL is always an advantage.

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Java 8 New Features: Map Reduce Made Easy With Stream APIs

April 20th, 2014 1 comment

In my article, I introduced the new Stream API. With the new stream APIs, you can apply many different operations on the stream, including the map-reduce functions.

One of the most famous framework to support map-reduce for large scale data processing, a.k.a. BigData, is Hadoop as I introduced almost two years ago here. Data processing wise, the Java 8 stream API can do pretty much the same. Here is a quick sample that shows how it count number of words in string. There are significant differences in how they are implemented and the cases in which they should be used. Let’s discuss them after the sample.

Java 8 New Features: Stream API

April 7th, 2014 No comments

Java Collections APIs consists of well designed classes and interfaces for managing all sorts of data structures. With Java 8, there is a new enhancement called Stream API related to the Collection APIs (see What’s New in JDK 8). I spent some time to study the new feature last week as part of my effort to bring myself up to date with Java 8.

Java 8 New Features: Method Reference

March 31st, 2014 2 comments

Coming with lambda feature in Java 8 is the method reference feature. It allows programmers to use methods as variables, and parameters to other methods. It works for class constructors too, where the method name is unanimously “new.’

There are four types of method references per Oracle documentation. Syntax wise, they all look similar with double colons as shown in the following sample code.

Java 8 New Features: Default Method

March 26th, 2014 No comments

Following the last article about Lambda feature in Java 8, I spent some more time on other features and will blog about them along the way. It’s a good way to push me to really think through and thus deepen my understanding. This article is about default method which is in fact related to the lambda feature.

Java 8 New Features: Lambda Expression

March 23rd, 2014 2 comments

On last Tuesday (March 18, 2014), Oracle released the Java SE 8. Here is the official documentation from the company on the new features in Java SE 8, ranging from language itself, libraries, tool, and run-time.

Reading X.509 Certificate in Java: How to Handle Format Issue

March 16th, 2014 14 comments

I got into a very interesting problem while writing code to read a X.509 certificate. It’s a standard PEM encoded certificate (shown below) as you would find anywhere else.

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

The exception is as follows. It’s pretty clear, but also confusing because the certificate string has included both BEGIN and END. It seems to me very complete. Of course, the program does not lie and we have to trust it most of the time unless there is a bug.

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Simplest Way to Encode Base64 in Java

February 3rd, 2014 4 comments

Base64 is a straight forward encoding for binary data into readable characters (RFC 4648 and RFC 2045). Although you can do it by yourself, more often than not you would like use an existing library, for example, Apache common. If you just need the Base64 encoding but have to import the whole library, it’s not a good idea. There is actually a better way without introducing extra dependency, which is to hack Java standard library 1.6.

How to Monitor New Changes of Log File with Java

October 30th, 2013 1 comment

If you have a log file that you want to monitor the incremental changes, you can use the following simple code. Whatever new log entries written to the log will be quickly picked up and printed out to console. It does not interfere with the application that writes the log file. To test the code, you can use any text editor to append more entries to the end of log file (don’t forget to save it).

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How to Run Maven Based Java Application From Command Line

October 28th, 2013 2 comments

It’s pretty straight forward to run Maven based projects in NetBeans IDE. For some projects that involve console related capabilities, you have to run it from OS console. One example is projects that use the JANSI APIs for colorful console output (see my last post for a sample). If you run the code within IDE, you won’t see the colors as would in a console.

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