This post is next update in sequence of discussions regarding little known features of java. Please subscribe through email to get updated when next discussion goes live. And do not forget to express your views in comments section. Java is a safe programming language and prevents programmer from doing a …
Java SerialVersionUID example. Learn to create generate serialVersionUID for classes to be serialized. Learn to change serialversionuid correctly.
Learn to convert InputStream to String using Google guava IO’s ByteSource and CharStreams, BufferedReader, Scanner, and IOUtils classes.
Today the line between “app server” and “web server” is fuzzy. But people continue to use the terms differently, primarily for emphasis.
In software engineering, the decorator design pattern is used to add additional features or behaviors to a particular instance of a class without modifying the other instances of the same class. The decorator pattern is often useful for adhering to the Single Responsibility Principle, as it allows functionality to be …
Design patterns are used to solve the problems which occur in a pattern, we all know that, right? Also we know that behavioral design patterns are design patterns that identify common communication patterns between objects. One of such behavioral patterns is visitor pattern, which we are going to learn about …
Learn to store and fetch large objects such as images, videos and other documents. Learn to mapping objects to LOB, CLOB and other types
We know that what global variables or constants are, these are fields which are accessible application wide. In java, it is done usually done using defining “public static” fields. Here by adding final keyword, we can change the global variable to global constant. So easy, right? But what about javascript? …
The immutable strings help in achieving the required data safety and performance in a Java application with help of underlying string pool.
So far we have learned about securing spring application using login form based security, custom user details security and many more such security related concepts. In this post, I am giving an example of scenario where use is already authenticated via any third party application or tool e.g. site minder …
Learn to use the EntityManager’s getReference() and find() usages and differences, their behavior when the primary identifies does not exist.
Learn the difference between natural id and primary id, @NaturalId annotation and various APIs to load persistent and proxy entities.
JAX-RS Resteasy has automatic GZIP decompression support. If the client framework or a JAX-RS service receives a message body with a Content-Encoding of “gzip”, it will automatically decompress it. The client framework automatically sets the Accept-Encoding header to be “gzip, deflate”. So you do not have to set this header …
JAX-RS 2.0 has brought lots of improvement over previous version. One of major improvement is client API which was completely missing in JAX-RS 1.0. While it was easy to write a portable JAX-RS service, each JAX-RS implementation defined their own proprietary API. JAX-RS 2.0 fills in this gap with a …
If you are using RESTEasy 3.x.y which has been support for JAX-RS 2.0, and you are trying to write RESTEasy client then you can face this exception. Full stack trace might look like this: Exception in thread “main” java.lang.RuntimeException: java.lang.ClassNotFoundException: org.glassfish.jersey.client.JerseyClientBuilder at javax.ws.rs.client.ClientBuilder.newBuilder(ClientBuilder.java:103) at test.jaxrs2.Demo_JAXRS_2_Example.main(Demo_JAXRS_2_Example.java:14) Caused by: java.lang.ClassNotFoundException: org.glassfish.jersey.client.JerseyClientBuilder at …
We know that JAXB(Java Architecture for XML Binding) allows Java developers to map Java classes to XML representations. JAXB provides two main features: the ability to marshal Java objects into XML and the inverse, i.e. to unmarshal XML back into Java objects. JAXB mostly is used while implementing webservices or …
This exception occurs when you are using JAXB to marshal a Java object (collection type) to xml format. The stack trace looks like this in case of Lists. OR in the case of Maps. Exception in thread "main" com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 3 counts of IllegalAnnotationExceptions java.util.Map is an interface, and JAXB can't …
This exception occurs when you are using JAXB to marshal a Java object (collection type) to xml format. The stack trace looks like this: 1. Reason The above exception occurs because JAXB always expects a @XmlRootElement annotation on the entity, it gets to marshal. This is mandatory and can not …
Java examples to marshal and unmarshal the collection of objects of type List and Set implementations such as ArrayList or HashSet into XML.
Learn to use RESTEasy ContainerRequestFilter to create security filter which is able to to perform authentication and authorization on RESTEasy based web applications.
Java compiler rearranges the statements we write in a Java program for performance improvements. Learn to generate the byte code for a class file to see how they have been rearranged.
Learn Java Secure Hashing algorithms in-depth. Java examples of MD5, SHA256, SHA512, PBKDF2, BCrypt, SCrypt algorithms with salt to create secure passwords.
Learn the basics of CountDownLatch and how to use it in real-life applications, its methods and use it to control the flow of application.
Since Java 7, the try-with-resources statements allow declaring AutoCloseable resources in a try block that JVM will close automatically.
1. Reason The ObjectNotFoundException exception is thrown when we try to load an entity in hibernate with session.load() method and entity is not found. The exception trace looks like this: 2. Solution The correct way to solve this problem is to use session.get() method. The get() method will return null …
Polymorphism in Java is the ability to create member functions or fields that behaves differently in different programmatic contexts.
Java collection interview questions. These questions are most asked interview questions for beginners to medium level developers in Java interviews.
The Path class, introduced in the Java SE 7 release, is one of the primary entry points of the java.nio.file package. If our application uses Java New IO, we should learn more about the powerful features available in this class. In this Java tutorial, we are learning 6 ways to …
Learn to configure and use the Ehcache library as the second-level cache provider for our hibernate application with an example.
1. Reason While working on post “Named queries in hibernate“, I encountered this error. Hibernate entity I coded was like this: And the error was: 2. Solution The problem is with the entity names in most of the cases. Actually, we have to follow HQL syntax, and it tells us …
Learn to create, group and execute named HQL and named native SQL queries in Hibernate using @NamedQuery and @NamedNativeQuery annotations.
The hibernate second-level cache is separate from the first-level cache and is available to be used globally in SessionFactory scope.
The first level cache (enabled by default) helps Hibernate to reduce the number of queries made to the database to improve the performance.
Learn to insert an object into the database using hibernate’s Session interface, JPA’s EntityManager and HQL Query interface with examples.
Security is an integral part of any enterprise application. Security involves two phases i.e. authentication and authorization. Authentication verifies who you are. Authorization verifies what you are authorized to do. In this post, we will learn to build role based basic authentication/ authorization security for REST APIs. Sections in this …
Learn to read and write excel files in Java using Apache POI library – with examples. Learn to add and evaluate formula cells and add color formatting also.
HashMap interview questions and ConcurrentHashMap interview questions. Learn questions like how hashmap works, rehashing in concurrenthashmap and more.
Let us identify 8 such warning signs, which will provide us with subtle hints that a particular test/suit should be improved.
Learn SOLID principles in Java with examples. Single Responsibility Principle, Open Closed Principle, Liskov’s Substitution Principle, Interface Segregation Principle, Dependency Inversion Principle.
This Jersey tutorial will help you set up the Jersey environment in your local machine and get started with a simple Hello World REST API.
ETags or entity tags are useful HTTP headers which can help in building a super fast application by minimizing the server load on system. ETag is set to the response to the client so a client can use various control request headers such as If-Match and If-None-Match for conditional requests. …
I have been facing this issue from quite long time as I didn’t took care of it. Everytime I faced this issue, I just went and changed the project compiler level for projects facets menu in eclipse. Today, I decided to end this for all. This error looks like in …
If you have started working on Jersey then you might face this issue while configuring it. This is the result of insufficient project dependencies on runtime. This issue is likely to be faced in the tomcat server. The Error The error log will look like this. SEVERE: Servlet /JerseyHelloWorld threw …
ToStringBuilder is a utility class provided by apache commons lang library. ToStringBuilder is a utility class provided by apache commons lang library. It provides a consistent and better control over what and how much data, an object should expose using toString() method and in which format. It can also help …
Learn to create and handle custom exceptions using resteasy ExceptionMapper interface implementations. It must be annotated with @Provider to work.
Launch4j is a cross-platform tool for wrapping Java applications distributed as jars in lightweight Windows native executable files. In this post, we will learn making such an executable file for a demo java application. Step1 ) Create a java application I am creating a very basic java class which simply …
The Bean Validation API (JSR-303) defines a meta-data model and API for bean validation based on annotations. The functionality is achieved through the resteasy-hibernatevalidator-provider component. In order to integrate, we need to add resteasy-hibernatevalidator-provider.jar and hibernate-validator.jar files to the classpath. If you are using maven the, you need to add …
RESTEasy can generate a JavaScript API that uses AJAX calls to invoke JAX-RS operations. Learn to use JSAPIServlet with examples.
Excessive logging is a common cause of performance degradation of applications. It is one of the best practices to ensure proper logging within your Java EE application implementation. However, be careful with the logging level that you enable in your production environment. Excessive logging will trigger high IO on your …
Spring send email program for explaing the usage of javamailsender interface of javax.mail dependency. Send email example in Java using Spring framework.
HowToDoInJava provides tutorials and how-to guides on Java and related technologies.
It also shares the best practices, algorithms & solutions and frequently asked interview questions.