org.testifyproject.bytebuddy.agent.Attacher Maven / Gradle / Ivy
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package org.testifyproject.bytebuddy.agent;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.lang.reflect.InvocationTargetException;
/**
* A Java program that attaches a Java agent to an external process.
*/
public class Attacher {
/**
* Base for access to a reflective member to make the code more readable.
*/
private static final Object STATIC_MEMBER = null;
/**
* The name of the {@code attach} method of the {@code VirtualMachine} class.
*/
private static final String ATTACH_METHOD_NAME = "attach";
/**
* The name of the {@code loadAgent} method of the {@code VirtualMachine} class.
*/
private static final String LOAD_AGENT_METHOD_NAME = "loadAgent";
/**
* The name of the {@code detach} method of the {@code VirtualMachine} class.
*/
private static final String DETACH_METHOD_NAME = "detach";
/**
* Runs the attacher as a Java application.
*
* @param args A list containing the fully qualified name of the virtual machine type,
* the process id, the fully qualified name of the Java agent jar followed by
* an empty string if the argument to the agent is {@code null} or any number
* of strings where the first argument is proceeded by any single character
* which is stripped off.
*/
@SuppressFBWarnings(value = "REC_CATCH_EXCEPTION", justification = "Exception should not be rethrown but trigger a fallback")
public static void main(String[] args) {
try {
String argument;
if (args[3].isEmpty()) {
argument = null;
} else {
StringBuilder stringBuilder = new StringBuilder(args[3].substring(1));
for (int index = 4; index < args.length; index++) {
stringBuilder.append(' ').append(args[index]);
}
argument = stringBuilder.toString();
}
install(Class.forName(args[0]), args[1], args[2], argument);
} catch (Exception ignored) {
System.exit(1);
}
}
/**
* Installs a Java agent on a target VM.
*
* @param virtualMachineType The virtual machine type to use for the external attachment.
* @param processId The id of the process being target of the external attachment.
* @param agent The Java agent to attach.
* @param argument The argument to provide or {@code null} if no argument is provided.
* @throws NoSuchMethodException If the virtual machine type does not define an expected method.
* @throws InvocationTargetException If the virtual machine type raises an error.
* @throws IllegalAccessException If a method of the virtual machine type cannot be accessed.
*/
protected static void install(Class virtualMachineType,
String processId,
String agent,
String argument) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
Object virtualMachineInstance = virtualMachineType
.getMethod(ATTACH_METHOD_NAME, String.class)
.invoke(STATIC_MEMBER, processId);
try {
virtualMachineType
.getMethod(LOAD_AGENT_METHOD_NAME, String.class, String.class)
.invoke(virtualMachineInstance, agent, argument);
} finally {
virtualMachineType
.getMethod(DETACH_METHOD_NAME)
.invoke(virtualMachineInstance);
}
}
/**
* The attacher provides only {@code static} utility methods and should not be instantiated.
*/
private Attacher() {
throw new UnsupportedOperationException();
}
}