Application examples of Spring ASM framework in the Java library
Application examples of Spring ASM framework in the Java library
Introduction:
The Spring ASM framework is a lightweight Java bytecode operation and analysis framework that allows you to dynamically modify and operate the byte code when loading the class.In the Java class library, the Spring ASM framework is often used to provide more flexible classes extension and enhanced functions. At the same time, it can also be operated at the bytecode level to achieve more efficient and accurate performance optimization.
Applications:
The following will introduce two application instances of the Spring ASM framework in the Java class library.
1. Dynamic generation proxy class:
In the Java class library, we often need to use agency mode to implement some functions, such as log records and transaction management.The Spring ASM framework can realize the proxy mode by dynamically generating proxy classes.The following is an example code:
public interface UserService {
void saveUser(User user);
}
public class UserServiceImpl implements UserService {
public void saveUser(User user) {
// Save user logic
}
}
public class UserServiceProxy implements UserService {
private UserService userService;
public UserServiceProxy(UserService userService) {
this.userService = userService;
}
public void saveUser(User user) {
// Do some pre -operation before preserving the user
System.out.println ("front operation");
// Call the actual preservation user method
userService.saveUser(user);
// After saving the user, do some rear operations
System.out.println ("rear operation");
}
}
public class UserServiceProxyGenerator {
public static UserService createProxy(UserService userService) {
ClassReader classReader;
try {
classReader = new ClassReader(userService.getClass().getName());
} catch (IOException e) {
throw new RuntimeException("Failed to read class file");
}
ClassWriter classWriter = new ClassWriter(classReader, ClassWriter.COMPUTE_FRAMES);
ClassVisitor classVisitor = new ClassVisitor(Opcodes.ASM8, classWriter) {
@Override
public MethodVisitor visitMethod(int access, String name, String descriptor,
String signature, String[] exceptions) {
if ("saveUser".equals(name)) {
MethodVisitor methodVisitor = cv.visitMethod(access, name, descriptor,
signature, exceptions);
return new MethodVisitor(api, methodVisitor) {
@Override
public void visitCode() {
// Insert the code before the method execution
mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out",
"Ljava/io/PrintStream;");
MV.VISITLDCINSN ("Pre -operation");
mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream",
"println", "(Ljava/lang/String;)V", false);
super.visitCode();
}
@Override
public void visitInsn(int opcode) {
if (opcode == Opcodes.RETURN) {
// Insert the code of the rear operation after the method execution
mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out",
"Ljava/io/PrintStream;");
mvisitldcinsn ("rear operation");
mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream",
"println", "(Ljava/lang/String;)V", false);
}
super.visitInsn(opcode);
}
};
}
return super.visitMethod(access, name, descriptor, signature, exceptions);
}
};
classReader.accept(classVisitor, ClassReader.EXPAND_FRAMES);
byte[] classBytes = classWriter.toByteArray();
Class<?> proxyClass = new ClassLoader() {
public Class<?> defineClass(String name, byte[] bytes) {
return defineClass(name, bytes, 0, bytes.length);
}
}.defineClass(userService.getClass().getName() + "$Proxy", classBytes);
try {
return (UserService) proxyClass.getDeclaredConstructors()[0].newInstance(userService);
} catch (InstantiationException | IllegalAccessException |
InvocationTargetException | IllegalArgumentException e) {
throw new RuntimeException("Failed to create proxy object");
}
}
}
// Use dynamically generated proxy classes
public class ExampleMain {
public static void main(String[] args) {
UserService userService = new UserServiceImpl();
UserService proxy = UserServiceProxyGenerator.createProxy(userService);
proxy.saveUser(new User());
}
}
In the above code, we define a `UserService` interface and a` UserServiceIMPL` class as the original object, and then dynamically generate the proxy class `UserserViceProxyGenerator`.The proxy class implements the `userService` interface, and inserts the code of the front operation and rear operation before and after saving the user method.Finally, in the `ExampleMain` class, we initialize the original object and call the user method through the proxy class.
2. Static method enhancement:
Sometimes we may need to inject some functions in static methods of a certain class, such as monitoring and performance statistics.The Spring ASM framework can help us enhance the static method at the bytecode level.Here are a sample code that enhances static methods:
public class MathUtils {
public static int add(int a, int b) {
return a + b;
}
}
public class MathUtilsEnhancer {
public static void enhanceAddMethod() {
ClassReader classReader;
try {
classReader = new ClassReader(MathUtils.class.getName());
} catch (IOException e) {
throw new RuntimeException("Failed to read class file");
}
ClassWriter classWriter = new ClassWriter(classReader, ClassWriter.COMPUTE_FRAMES);
ClassVisitor classVisitor = new ClassVisitor(Opcodes.ASM8, classWriter) {
@Override
public MethodVisitor visitMethod(int access, String name, String descriptor,
String signature, String[] exceptions) {
if ("add".equals(name)) {
MethodVisitor methodVisitor = cv.visitMethod(access, name, descriptor,
signature, exceptions);
return new MethodVisitor(api, methodVisitor) {
@Override
public void visitCode() {
// Insert the monitoring code before the method execution
mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out",
"Ljava/io/PrintStream;");
mvISITLDCINSN ("Monitoring Start");
mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream",
"println", "(Ljava/lang/String;)V", false);
super.visitCode();
}
@Override
public void visitInsn(int opcode) {
if (opcode >= Opcodes.IADD && opcode <= Opcodes.LREM) {
// Insert performance statistics code after each addition and subtraction instruction
mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out",
"Ljava/io/PrintStream;");
MV.VISITLDCINSN ("Performance Statistics");
mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream",
"println", "(Ljava/lang/String;)V", false);
}
super.visitInsn(opcode);
}
};
}
return super.visitMethod(access, name, descriptor, signature, exceptions);
}
};
classReader.accept(classVisitor, ClassReader.EXPAND_FRAMES);
byte[] classBytes = classWriter.toByteArray();
try {
FileOutputStream fos = new FileOutputStream("MathUtils.class");
fos.write(classBytes);
fos.close();
} catch (IOException e) {
throw new RuntimeException("Failed to write class file");
}
// The enhanced mathutils class will be output to the mathutils.class file in the current directory
}
}
// Use the enhanced static method
public class ExampleMain {
public static void main(String[] args) {
MathUtilsEnhancer.enhanceAddMethod();
int result = MathUtils.add(1, 2);
System.out.println("Result: " + result);
}
}
In the above code, we define a `mathutils` class and realize a static method of adding method` add`.Then through the `Mathutilsenhancer` class, we enhanced the` adD` method with the Spring ASM framework.Before the method execution, we inserted a monitoring code and inserted a performance statistical code after each addition and subtraction instructions.Finally, in the `ExampleMain` class, we tested the enhanced static method and output the result.
Summarize:
The application of the Spring ASM framework in the Java library is very wide. It can help us realize the dynamic generation of proxy classes and enhance static methods at the bytecode level.By operating bytecode, we can achieve more flexible class extensions and enhancement, and at the same time, we can also improve performance and achieve more accurate optimization.In actual development, we can flexibly use the Spring ASM framework to improve the quality and performance of the code according to specific needs, so as to better meet business needs.
