org.objectweb.asm2.package.html Maven / Gradle / Ivy
Provides a small and fast bytecode manipulation framework.
The ASM framework is organized
around the {@link org.objectweb.asm.ClassVisitor ClassVisitor},
{@link org.objectweb.asm.FieldVisitor FieldVisitor} and
{@link org.objectweb.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 org.objectweb.asm2.ClassReader
ClassReader} class, that can parse an existing class and make a given visitor visit it. ASM also
provides a {@link org.objectweb.asm2.ClassWriter ClassWriter} class, which is a visitor that
generates Java class files.
In order to generate a class from scratch, only the {@link
org.objectweb.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 org.objectweb.asm2.ClassReader
ClassReader} class to analyze the original class, a class modifier, and a {@link
org.objectwebasm2m.ClassWriter ClassWriter} to construct the modified class. The class modifier
is just a {@link org.objectweasm2sm.ClassVisitor ClassVisitor} that delegates most of the work to
another {@link org.objectweb.asm2.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
org.objectasm2.asm.ClassAdapter ClassAdapter} and {@link org.objectweb.asm2.MethodAdapter
MethodAdapter} classes, which implement the {@link org.objectasm2.asm.ClassVisitor ClassVisitor}
and {@link org.objeasm2eb.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