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package jdk.internal.reflect;

import java.security.AccessController;
import java.security.PrivilegedAction;
import jdk.internal.misc.Unsafe;

Utility class which assists in calling Unsafe.defineClass() by creating a new class loader which delegates to the one needed in order for proper resolution of the given bytecodes to occur.
/** Utility class which assists in calling Unsafe.defineClass() by creating a new class loader which delegates to the one needed in order for proper resolution of the given bytecodes to occur. */
class ClassDefiner { static final Unsafe unsafe = Unsafe.getUnsafe();

We define generated code into a new class loader which delegates to the defining loader of the target class. It is necessary for the VM to be able to resolve references to the target class from the generated bytecodes, which could not occur if the generated code was loaded into the bootstrap class loader.

There are two primary reasons for creating a new loader instead of defining these bytecodes directly into the defining loader of the target class: first, it avoids any possible security risk of having these bytecodes in the same loader. Second, it allows the generated bytecodes to be unloaded earlier than would otherwise be possible, decreasing run-time footprint.

/** <P> We define generated code into a new class loader which delegates to the defining loader of the target class. It is necessary for the VM to be able to resolve references to the target class from the generated bytecodes, which could not occur if the generated code was loaded into the bootstrap class loader. </P> <P> There are two primary reasons for creating a new loader instead of defining these bytecodes directly into the defining loader of the target class: first, it avoids any possible security risk of having these bytecodes in the same loader. Second, it allows the generated bytecodes to be unloaded earlier than would otherwise be possible, decreasing run-time footprint. </P> */
static Class<?> defineClass(String name, byte[] bytes, int off, int len, final ClassLoader parentClassLoader) { ClassLoader newLoader = AccessController.doPrivileged( new PrivilegedAction<ClassLoader>() { public ClassLoader run() { return new DelegatingClassLoader(parentClassLoader); } }); return unsafe.defineClass(name, bytes, off, len, newLoader, null); } } // NOTE: this class's name and presence are known to the virtual // machine as of the fix for 4474172. class DelegatingClassLoader extends ClassLoader { DelegatingClassLoader(ClassLoader parent) { super(parent); } }