Java Annotation

By -
Annotation in Java is there to make programmers life a bit easy.
Annotation-based development relieves Java developers from the pain of cumbersome configuration.

Advantages of using Annotations
  • Annotations are attached to Classes and can be processed via reflection.
  • It is much easier to see the Annotations as they are defined in Java code and no need to refer external configurations (like XML).
  • Compiler will do static type checking for Annotation uses. Compile time the proper uses of annotation will be done.
Here are some rules-of-thumb when defining an annotation type:

Annotation declaration should start with an 'at' sign like @, following with an interface keyword, following with the annotation name.
Method declarations should not have any parameters.
Method declarations should not have any throws clauses.
Return types of the method should be one of the following:
  • primitives
  • String
  • Class
  • enum
  • array of the above types

The following shows example of deceleration an annotation.
1
2
3
4
5
public @interface RestAPIRequestLog {
    int id();
    String requestIp();
    String requestLanguage(); default "[en]"; 
}

An annotation type with no elements is termed a marker annotation type, for example:

public @interface RestAPIMonitored { }

In annotations with a single element, the element should be named
value, as shown below:


1
2
3
public @interface SecuredRestAPI {
 String token();
}

Comments

Post a Comment

Popular posts from this blog

Difference between volatile and synchronized

By -
volatile is a field modifier, while synchronized modifies code blocks and methods. So we can specify three variations of a simple accessor using those two keywords: int i1; int geti1() {return i1;} volatile int i2; int geti2() {return i2;} int i3; synchronized int geti3() {return i3;} geti1() accesses the value currently stored in i1 in the current thread . Threads can have local copies of variables, and the data does not have to be the same as the data held in other threads. In particular, another thread may have updated i1 in it's thread, but the value in the current thread could be different from that updated value. In fact Java has the idea of a "main" memory, and this is the memory that holds the current "correct" value for variables. Threads can have their own copy of data for variables, and the thread copy can be different from the "main" memory. So in fact, it is possible for the "main"
Read more

Converting Java Map to String

By -
Java Collections framework, String manipulation etc is something that we often encounter in Development process. For processing collections (like checking null/empty, Intersection, Disjunction) We do have some of the very use full libraries. Some of the Collection related libraries are Apche Commons Collections and Google  Collections(Guava). Problem Use Case This article explains how to convert a Java Map to String(and vice versa) using different libraries and technique. One way is to use StringBuilder(Or String) and loop though the Map and build the String by applying some sort of separator ( for key:value and entry). Here we have to take care of the null value etc. Without Any Library If we want to convert the map to a String with key value separator and also individual entry seperator in the resulting String, we have to write code for that. For a simple Map, we have to iterate though the map, take care of the null values etc. Following is a sample to get String built
Read more

Masking Credit Card number in Java

By -
Sometimes we need to mask crucial information like Credit Card Numbers, CVV numbers etc before storing  or logging the information. This example mask Credit Card Number (Except last 4 Digit) from a Text which contains information along with Credit Card Number. The following example demonstrates how we can easily mask the credit card with Matcher and Pattern Classes. This Sample Code uses Matcher and Pattern. Pattern Used in this sample is not optimized for Credit Card Numbers, this pattern will get any numerical numbers in the String Content.  Based on the Credit Card Type a more efficient and Strict RegEx can be used to mask the Credit Card. /**Mask the Credit card number but last four digit value **/   Pattern PATTERN = Pattern.compile( "[0-9]+" ); String message = content; Matcher matcher = PATTERN.matcher(message); String maskingChar = "*"; StringBuilder finalMask = new StringBuilder(maskingChar);
Read more