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Hibernate / JPA Lazy Loading Pitfalls

Hibernate provides different kinds of relationships between entities like OneToMany, ManyToOne, ManyToMany or OneToOne. In the early days of Hibernate the fething strategy of all relationships was “lazy”. This stayed true for a long time and changed when Hibernate started to support JPA, because the JPA specification defines different default fetching strategies. The default fetching strategy up to Hibernate version 4.3 is: By default, Hibernate uses lazy select fetching for collections and lazy proxy fetching for single-valued associations. These defaults make sense for most associations in the majority of applications. Hibernate 4.3 manual, 20.1.1. Working with lazy associations In contrast to this the JPA specification specifies different default fetching strategies per… Read More »Hibernate / JPA Lazy Loading Pitfalls

Impact of proxy on equals and hashCode

A lot of frameworks create proxies  to apply aspect oriented programming or the lazy loading pattern. Hibernate for example uses cglib or javasissit to create lazy loading proxies. The famous springframework mainly uses java proxyies created via java.lang.reflect.Proxy.newProxyInstance(ClassLoader, Class<?>[], InvocationHandler) or cglib as well. Therefore it is important to know exactly how proxies work and the impact of proxies on your implementations. Especially when implementing basic methods like equals() and hashCode(). How proxies work A proxy is (like the name implies) not the real object. It is another object with the same interface as the real object. Since it has the same interface it can either delegate all calls to… Read More »Impact of proxy on equals and hashCode

Handling complex object state with design

Some APIs that implement a complex object state management often violate the single responsibility principle and make the usage very difficult. When you do all aspects of the complex state management in one inferface the interface’s methods must be invoked in the chronological correct order. Such APIs are hard to understand and to integrate. What we really want are APIs that guide the client code programmers in such situations. Lets take a look at an API that breaks the single responsibility principle and let us think about the consequences for the client code programmer. If you take a look at the FTPClient API of apache commons you can see that all… Read More »Handling complex object state with design

The difference between pojos and java beans

Java Beans and Pojos are often used and misunderstood terms. Some think that a pojo is a java bean and vice versa. In fact it is not. There are differences that matter. The pojo If you want to know what a term really means you have to find the source context in which the term has been created. So for the term pojo it was originally created by Martin Fowler, Rebecca Parsons and Josh MacKenzie at a time when J2EE had it’s hype. At that time J2EE developer were more busy with technology instead of concentrating on the business value. The problem arised because J2EE requires a lot of techology code in your… Read More »The difference between pojos and java beans