package net.bytebuddy.agent;
import java.lang.instrument.Instrumentation;
/**
* An installer class which defined the hook-in methods that are required by the Java agent specification.
*/
public class Installer {
/**
* A field for carrying the {@link java.lang.instrument.Instrumentation} that was loaded by the Byte Buddy
* agent. Note that this field must never be accessed directly as the agent is injected into the VM's
* system class loader. This way, the field of this class might be {@code null} even after the installation
* of the Byte Buddy agent as this class might be loaded by a different class loader than the system class
* loader.
*/
@SuppressWarnings("unused")
private static volatile Instrumentation instrumentation;
/**
* The installer provides only {@code static} hook-in methods and should not be instantiated.
*/
private Installer() {
throw new UnsupportedOperationException();
}
/**
* <p>
* Returns the instrumentation that was loaded by the Byte Buddy agent. When a security manager is active,
* the {@link RuntimePermission} for {@code getInstrumentation} is required by the caller.
* </p>
* <p>
* <b>Important</b>: This method must only be invoked via the {@link ClassLoader#getSystemClassLoader()} where any
* Java agent is loaded. It is possible that two versions of this class exist for different class loaders.
* </p>
*
* @return The instrumentation instance of the Byte Buddy agent.
*/
public static Instrumentation getInstrumentation() {
SecurityManager securityManager = System.getSecurityManager();
if (securityManager != null) {
securityManager.checkPermission(new RuntimePermission("getInstrumentation"));
}
Instrumentation instrumentation = Installer.instrumentation;
if (instrumentation == null) {
throw new IllegalStateException("The Byte Buddy agent is not loaded or this method is not called via the system class loader");
}
return instrumentation;
}
/**
* Allows the installation of this agent via a command line argument.
*
* @param agentArguments The unused agent arguments.
* @param instrumentation The instrumentation instance.
*/
public static void premain(String agentArguments, Instrumentation instrumentation) {
Installer.instrumentation = instrumentation;
}
/**
* Allows the installation of this agent via the Attach API.
*
* @param agentArguments The unused agent arguments.
* @param instrumentation The instrumentation instance.
*/
@SuppressWarnings("unused")
public static void agentmain(String agentArguments, Instrumentation instrumentation) {
Installer.instrumentation = instrumentation;
}
}