In this article we are going to see the apt commands.
What is apt?
apt is a java annotation processor which are used in the source file using reflective API. APT stands for annotation processing tool.
This provides a build time , source based, read only view of programs structure that follows java generics.
First apt determines used annotations, then look annotation processing factories and get what annotations they process , then ask a factory to provide an annotation processor .
That creates new source code/other files. If the processors have generated new source files, apt will repeat this process until no new source files are generated.
apt [options] [source file
apt Options :
apt accepts all javac options. Following are apt specific options.
- s (dir) : Set root directory for generated source(sub-directories are created based on package) -nocompile : Do not compile source to class .
- print : Prints (as text) specified types and performs no annotation processing or compilation.
- A(key(=val)) : Key and value passing to annotation processor(Not interpreted by apt , but set for individual processors)
- factorypath (path): Set path to find annotation processor factories(classpath is not searched for factories)
- factory (classname) : Used Annotation Processor Factory Name
Debugging apt options :
- XListAnnotationTypes : Shows found annotation types
- XListDeclarations : Shows declarations
- XPrintAptRounds : Prints initial and recursive apt rounds
- XPrintFactoryInfo : Prints about annotations that asked a factory to process
Shared javac’s options:
- d (dir) : Set location to place processor and javac generated classes.
- cp/-classpath (path) : Specify where to find class files and annotation processor factories.
Use of annotation and processing :
- Framework implementation(annotations in a framework perform some task depend on annotations. Ex-spring, hibernate or others.)
- Reporting(making reports function results like Unit Test results, program output, application/function states) with different type of files.
- Debugging(to see inner states of the functions with annotations)
- Run time processing
- Compile time and Deploy time processing
- Compiler state information.