Java Serialization Enhancer
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Seren : the Java Serialization Enhancer

Seren (SERialization ENhancer) aims to enhance your classes so that they are much quicker to serialize. It does so by instrumenting the classes at load-time to generate optimized writeObject / readObject methods, based on some best practices seen in the JavaSpecialist Master Course.

Which classes should be enhanced is determined by a "filter", which is configured in the "" configuration file (see below).

In each selected class, Seren will detect and optimize all non-static, non-transient fields (as the standard serialization system does).

Building Seren

To compile the library and package it as a jar :

mvn clean compile package

To run the integration tests (after the library has been packaged) :

mvn verify


To know which classes to instrument, Seren needs you to configure a "class filter". Some of the most commonly needed are provided for your convenience (see the javadoc for a list of available filters and their configuration options), but you can very easily write your own if required.

A class filter is defined by a logical name, and an optional set of configuration properties specific to this filter.

All this configuration takes place in the "" file, which must be placed at the root of the classpath. You can configure several filters in this file; only the one specified by the "seren.filter" property will be used.

The syntax is easy :



For example :

// Configure which filter will be used

// The selected filter's configuration

// Another filter configuration - won't be used

One othe configuration option is the "seren.verbose" parameter, which can be set to true or false (default). In verbose mode, both the filter and the transformer print extra information on the standart output stream (console).


Running Seren

To run your application with Seren, just add the following option to the command line. Also, make sure the Javassist library (javassist.jar) is available in the classpath.


For example :

java -cp <classpath> -javaagent:/home/olivier/seren.jar

Developing a custom class filter

Class filters must implement the net.thecodersbreakfast.seren.filter.ClassFilter interface, that defines two methods :

    public void configure(Map<String,String> config) throws Exception;
    public boolean acceptClass(ClassLoader classLoader, CtClass classDefinition) throws Exception;

The "configure" method is called after the Filter is instanciated. The Map passed as a parameter contains the filter's properties defined in the configuration file; its keys are the names of the properties related to this particular filter, minus the filter's prefix (filter.).

The "acceptClass" method is then called for each loaded class. It's up to you to use the provided class definition (a Javassist CtClass instance) to determine if it should be instrumented. It is recommended to used BaseClassFilter (net.thecodersbreakfast.seren.filter.BaseClassFilter) as a superclass for all filters, as it provides utility methods and performs some basic checks, such as verifying if the class is actually a class (not an enum, interface, etc.) and if it implements Serializable.

As an example, below is the code of the PackageListFilter filter :

    public class PackageListFilter extends BaseClassFilter {

        private Set<String> packages = new HashSet<String>();

        public void configure(Map<String, String> config) {
            String packageNames = config.get("packages");

        public boolean acceptClass(ClassLoader classLoader, CtClass classDefinition) throws Exception {
            return super.acceptClass(classLoader, classDefinition) && packages.contains(classDefinition.getPackageName());

Licence & Contact info

This library is licenced under the 3-clause BSD Licence (see the attached LICENCE file).

IANAL, but this means (roughly) that you can freely use SEREN in your personal or commercial product, in source or binary form, provided you distribute the unmodified licence file with it, make clear I am the original author, and do not use my name or the library name to promote your own products. Oh, and if it explodes in production, I don't have anything to do with it :)

For any question, please contact me at olivier(@)