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Provides a small and fast bytecode manipulation framework.
The ASM framework is organized
around the {@link com.uwyn.rife.asm.ClassVisitor ClassVisitor},
{@link com.uwyn.rife.asm.FieldVisitor FieldVisitor} and
{@link com.uwyn.rife.asm.MethodVisitor MethodVisitor} interfaces, which allow
one to visit the fields and methods of a class, including the bytecode
instructions of each method.
In addition to these main interfaces, ASM provides a {@link
com.uwyn.rife.asm.ClassReader ClassReader} class, that can parse an
existing class and make a given visitor visit it. ASM also provides
a {@link com.uwyn.rife.asm.ClassWriter ClassWriter} class, which is
a visitor that generates Java class files.
In order to generate a class from scratch, only the {@link
com.uwyn.rife.asm.ClassWriter ClassWriter} class is necessary. Indeed,
in order to generate a class, one must just call its visitXXX
methods with the appropriate arguments to generate the desired fields
and methods. See the "helloworld" example in the ASM distribution for
more details about class generation.
In order to modify existing classes, one must use a {@link
com.uwyn.rife.asm.ClassReader ClassReader} class to analyze
the original class, a class modifier, and a {@link com.uwyn.rife.asm.ClassWriter
ClassWriter} to construct the modified class. The class modifier
is just a {@link com.uwyn.rife.asm.ClassVisitor ClassVisitor}
that delegates most of the work to another {@link com.uwyn.rife.asm.ClassVisitor
ClassVisitor}, but that sometimes changes some parameter values,
or call additional methods, in order to implement the desired
modification process. In order to make it easier to implement such
class modifiers, ASM provides the {@link com.uwyn.rife.asm.ClassAdapter
ClassAdapter} and {@link com.uwyn.rife.asm.MethodAdapter MethodAdapter}
classes, which implement the {@link com.uwyn.rife.asm.ClassVisitor ClassVisitor}
and {@link com.uwyn.rife.asm.MethodVisitor MethodVisitor} interfaces by
delegating all work to other visitors. See the "adapt" example in the ASM
distribution for more details about class modification.
The size of the core ASM library, asm.jar, is only 31KB, which is much
more smaller than
the size of the BCEL library (350KB
without the class verifier), and than the size of the
SERP library (150KB). ASM is also
much more faster than these tools. Indeed the overhead of a load time class
transformation process is of the order of 60% with ASM, 700% or more with BCEL,
and 1100% or more with SERP (see the test/perf directory in the ASM
distribution)!
@since ASM 1.3
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