Category Archives: Java

Hibernate internals – how does pagination work?

Hibernate supports pagination for all query types – HQL, Criteria and SQL, via the query setMaxResults() and setFirstResult() methods, but how does this work under the covers? Well, assuming your database supports it, it will add a row_number() to your … Continue reading

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Memory leak with TestNG and Spring DirtiesContext annotation

We recently added some new integration tests to our test suite. All three tests were Spring integration tests. Normally in a Spring integration test, the entire code for a test method operates in a single transaction, and at the end … Continue reading

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IntelliJ Hints and Tips

Most useful keyboard shortcuts (these are for Mac): CMD + O Open class CMD + SHIFT + OOpen file CMD + F Find in file CMD + R Replace in file CMD + SHIFT + F Find in path CMD … Continue reading

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log4j in maven tests

If you want to specify log4j configuration when running tests via Maven, you can do so by updating the Maven surefire plugin configuration to point to a specific log4j configuration file. For log4j v2 the appropriate parameter is called log4j.configuration. … Continue reading

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Generating code with JavaPoet

Why write code when you can generate it? There are lots of situations when it makes more sense to generate. In this article I’m going to work through an example of how to use JavaPoet and Apache BeanUtils to write … Continue reading

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Writing a custom spliterator in Java 8

In this article I’m going to give two examples of writing a custom spliterator in Java 8. What is a spliterator and why would you need to write your own? Well, a spliterator is used by the Java streams code … Continue reading

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Using Optional in Java 8

“The introduction of null references was my billion dollar mistake” – Tony Hoare Optional is a (typed) container object. It may contain a single object, or it may be empty. It allows you to avoid null pointer exceptions. In this … Continue reading

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Java 8 Streams Tutorial

In this tutorial, I’m going to start by explaining some of the basics of streams. Viz: What streams are Terminal and non-terminal operations Their “lazy” nature Their read-once nature Why they were introduced i.e. how they enable easy parallel operations … Continue reading

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Yet another Java 8 custom collector example

Java 8 introduces a number of functional programming techniques to the language. Collections can be turned into streams which allows you to perform standard functional operations on them, such as filtering, mapping, reducing and collecting. In this post I’m going … Continue reading

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Hibernate example 4 – many to many associations

I’ve put some code on Github that shows three ways of modelling many to many associations with JPA / Hibernate: Using a join table that is not mapped as either an entity or an embedded component type. Mapping the join … Continue reading

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