Class search path

The default ClassPool returned by a static method ClassPool.getDefault() searches the same path that the underlying JVM (Java virtual machine) has. If a program is running on a web application server such as JBoss and Tomcat, the ClassPool object may not be able to find user classes since such a web application server uses multiple class loaders as well as the system class loader. In that case, an additional class path must be registered to the ClassPool. Suppose that pool refers to aClassPool object:

pool.insertClassPath(new ClassClassPath(this.getClass())); 

This statement registers the class path that was used for loading the class of the object that this refers to. You can use any Class object as an argument instead ofthis.getClass(). The class path used for loading the class represented by that Class object is registered.

You can register a directory name as the class search path. For example, the following code adds a directory /usr/local/javalib to the search path:

ClassPool pool = ClassPool.getDefault(); pool.insertClassPath("/usr/local/javalib"); 

The search path that the users can add is not only a directory but also a URL:

ClassPool pool = ClassPool.getDefault(); ClassPath cp = new URLClassPath("www.javassist.org", 80, "/java/", "org.javassist."); pool.insertClassPath(cp); 

This program adds "http://www.javassist.org:80/java/" to the class search path. This URL is used only for searching classes belonging to a package org.javassist. For example, to load a class org.javassist.test.Main, its class file will be obtained from:

http://www.javassist.org:80/java/org/javassist/test/Main.class 

Furthermore, you can directly give a byte array to a ClassPool object and construct a CtClass object from that array. To do this, use ByteArrayClassPath. For example,

ClassPool cp = ClassPool.getDefault(); byte[] b = a byte array; String name = class name; cp.insertClassPath(new ByteArrayClassPath(name, b)); CtClass cc = cp.get(name); 

The obtained CtClass object represents a class defined by the class file specified by b. The ClassPool reads a class file from the given ByteArrayClassPath if get() is called and the class name given to get() is equal to one specified by name.

If you do not know the fully-qualified name of the class, then you can use makeClass() in ClassPool:

ClassPool cp = ClassPool.getDefault(); InputStream ins = an input stream for reading a class file; CtClass cc = cp.makeClass(ins); 

makeClass() returns the CtClass object constructed from the given input stream. You can use makeClass() for eagerly feeding class files to the ClassPool object. This might improve performance if the search path includes a large jar file. Since a ClassPool object reads a class file on demand, it might repeatedly search the whole jar file for every class file. makeClass() can be used for optimizing this search. The CtClass constructed by makeClass() is kept in the ClassPool object and the class file is never read again.

The users can extend the class search path. They can define a new class implementing ClassPath interface and give an instance of that class to insertClassPath() inClassPool. This allows a non-standard resource to be included in the search path.