Javassist (Java programming assistant) is a

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...

library A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...

providing a means to manipulate the

Java bytecode In computing, Java bytecode is the bytecode-structured instruction set of the Java virtual machine (JVM), a virtual machine that enables a computer to run programs written in the Java programming language and several other programming langua ...

of an application. In this sense Javassist provides the support for structural

reflection Reflection or reflexion may refer to: Science and technology * Reflection (physics), a common wave phenomenon ** Specular reflection, reflection from a smooth surface *** Mirror image, a reflection in a mirror or in water ** Signal reflection, in ...

, i.e. the ability to change the

implementation Implementation is the realization of an application, or execution of a plan, idea, model, design, specification, standard, algorithm, or policy. Industry-specific definitions Computer science In computer science, an implementation is a real ...

of a class at

run time Run(s) or RUN may refer to: Places * Run (island), one of the Banda Islands in Indonesia * Run (stream), a stream in the Dutch province of North Brabant People * Run (rapper), Joseph Simmons, now known as "Reverend Run", from the hip-hop group ...

. Bytecode manipulation is performed at

load-time In computer systems a loader is the part of an operating system that is responsible for loading programs and libraries. It is one of the essential stages in the process of starting a program, as it places programs into memory and prepares them f ...

through a provided class loader. Javassist enables Java programs to define a new class at runtime and to modify a class file when the JVM loads it. Unlike other similar bytecode editors, Javassist provides two levels of API: source level and bytecode level. Using the source-level API, programmers can edit a class file without knowledge of the specifications of the Java bytecode; the whole API is designed with only the vocabulary of the Java language. Programmers can even specify inserted bytecode in the form of Java source text; Javassist compiles it on the fly. On the other hand, the bytecode-level API allows the users to directly edit a class file as other editors.

Uses

Javassist can be used for the following: * For specifying the bytecode using source code – can compile a fragment of source text online (e.g., just a single statement) * For

aspect-oriented programming In computing, aspect-oriented programming (AOP) is a programming paradigm that aims to increase modularity by allowing the separation of cross-cutting concerns. It does so by adding behavior to existing code (an advice) ''without'' modifying th ...

(AOP) – can introduce new methods into a class and insert before/after/around advice at both the caller and callee sides * For

at runtime – can use a metaobject that controls method calls on base-level objects * For

remote method invocation In a distributed computing environment, distributed object communication realizes communication between distributed objects. The main role is to allow objects to access data and invoke methods on remote objects (objects residing in non-local memor ...

– can call a method on a remote object running on a web server, an alternative to Java RMI that does not need a stub compiler such as

References

External links

Java (programming language) libraries {{compu-lang-stub

Uses

See also

References

External links