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Author Archives: Michal Jastak

Michał is a Chief Technology Officer in Java Division of AIS.PL, company developing mostly Web Applications of different kind, usually e-Government related.

Spring MVC – HTTP message converter

Quite often you need to provide users with the same data, but in different forms, like JSON, PDF, XLS, etc. If your application is Spring Framework based, this task can be achieved using HTTP message converters. HTTP message converters are applied when HTTP request (or its parts) needs to be converted into type required for handler method argument (see: Handler ...

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JDBC – Emulating a sequence

Probably each of us encountered this problem at least once in the programmer’s life – how to emulate a database sequence? Below you may find my variation of this problem’s solution. Suppose that we have an interface defining the desired API for returning a sequence of integer numbers: 1 2 3 4 5 public interface Sequences {       int nextValue(String ...

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Serialization Proxy Pattern example

There are books, which change your life immensely. One of such books is “Effective Java” by Joshua Bloch. Below you may find small experiment, which was inspired by Chapter 11 of this book – “Serialization”. Suppose that we have a class designed for inheritance, which is not Serializable itself, and has no parameterless constructor, like in this example:     ...

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JPA – Querydsl Projections

In my last post: JPA – Basic Projections – I’ve mentioned about two basic possibilities of building JPA Projections. This post brings you more examples, this time based on Querydsl framework. Note, that I’m referring Querydsl version 3.1.1 here. Reinvented constructor expressions Take a look at the following code:         ... import static com.blogspot.vardlokkur.domain.QEmployee.employee; import javax.persistence.EntityManager; import ...

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JPA – Should I become a laziness extremist?

java-interview-questions-answers

When you spoke with the Developers about mapping objects to relational databases, they very often complain about poor JPA performance, unpredictable behavior of JPA Providers, etc. Usually at some point of the conversation you will hear: “Let’s drop this technology at all, we’ve seen something much better on the conference last month. We will use it in our projects instead ...

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JPA – Hibernate – Type mapping on package level

When we are finally mature enough to use some custom types mapping in JPA, we usually stuck with some provider specific solution, because JPA itself doesn’t define any mechanism for doing it. Let me show you an example of custom type mapping definition for one of the JPA providers – Hibernate. Suppose that we use Joda Money in our project, ...

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Spring’s Web MVC – Redirect to the Memory Leak

spring-interview-questions-answers

They say that one rock can cause an avalanche. Lately, one of my Colleagues, Marcin Radoszewski, gave me such a rock. You’ll probably never guess what it is, but there is a chance, that you use it in many of your Web Applications. Allow me to introduce this rock to you. You probably well know redirect after post pattern. Using ...

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Customize PMD in Eclipse with your own rules

PMD is very nice Java code scanner which helps you avoid potential programming problems. It can be easily extended to your needs, and this post will bring you simple example of custom PMD rules related to JPA’s @Enumerated annotation usage. Before you’ll continue the reading, you should check one of my previous posts – JPA – @Enumerated default attribute. When ...

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JSON – Jackson to the rescue

Sometimes you have to fetch some data from the server in JavaScript, JSON is pretty good choice for this task. Let’s play with the Employer – Employee – Benefit example from the post JPA Demystified (episode 1) – @OneToMany and @ManyToOne mappings. We will use it inside the web application based on Spring Framework. Our first controller will return the ...

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