最近有个需求,需要获取java方法参数的名称,网上查了下,然后自己也实践了下,总结出3点:
1.能不能获取方法参数的名称取决于class文件里是否含有LocalVariableTable。
2.javac编译生成的class文件不含有LocalVariableTable,但是eclipse编译生成的class文件却含有LocalVariableTable。
3.有2种方式可以获得,用Asm和Javassist,Asm的性能略高。
贴代码:
maven依赖:
<dependency> <groupId>org.javassist</groupId> <artifactId>javassist</artifactId> <version>3.18.0-GA</version> </dependency> <dependency> <groupId>org.ow2.asm</groupId> <artifactId>asm</artifactId> <version>4.1</version> </dependency>
User类:
/** * * @author <a href="mailto:yankai913@gmail.com">yankai</a> * @date 2013-7-17 */ public class User { String name; String address; int age; public User(String name, String address, int age) { this.name = name; this.address = address; this.age = age; } public static User newInstance(String name, String address, int age) { return new User(name, address, age); } public User copy(String name, String address, int age) { return new User(name, address, age); } }
asm实现:
import java.lang.reflect.Method; import java.lang.reflect.Modifier; import org.objectweb.asm.ClassReader; import org.objectweb.asm.ClassVisitor; import org.objectweb.asm.Label; import org.objectweb.asm.MethodVisitor; import org.objectweb.asm.Opcodes; /** * @author <a href="mailto:yankai913@gmail.com">yankai</a> * @date 2013-7-17 */ public class AsmTool { private static boolean sameType(Type[] types, Class<?>[] clazzes) { if (types.length != clazzes.length) { return false; } for (int i = 0; i < types.length; i++) { if (!Type.getType(clazzes[i]).equals(types[i])) { return false; } } return true; } public static String[] getMethodParamNames(final Method m) throws Exception { final String[] paramNames = new String[m.getParameterTypes().length]; String methodClass = m.getDeclaringClass().getName(); ClassReader cr = new ClassReader(methodClass); cr.accept(new ClassVisitor(Opcodes.ASM4) { @Override public MethodVisitor visitMethod(final int access, final String name, final String desc, final String signature, final String[] exceptions) { Type[] args = Type.getArgumentTypes(desc); if (!name.equals(m.getName()) || !sameType(args, m.getParameterTypes())) { return null; } return new MethodVisitor(Opcodes.ASM4) { @Override public void visitLocalVariable(String name, String desc, String signature, Label start, Label end, int index) { int i = index - 1; if (Modifier.isStatic(m.getModifiers())) { i = index; } if (i >= 0 && i < paramNames.length) { paramNames[i] = name; } } }; } }, 0); return paramNames; } }
asm测试:
import java.lang.reflect.Method; import java.util.Arrays; /** * * @author <a href="mailto:yankai913@gmail.com">yankai</a> * @date 2013-7-17 */ public class TestAsm { public static void main(String[] args) throws Exception { long start = System.currentTimeMillis(); final Method method = User.class.getMethod("newInstance", new Class<?>[]{String.class, String.class, int.class}); String[] s = AsmTool.getMethodParamNames(method); System.out.println(Arrays.toString(s)); System.out.println(System.currentTimeMillis() - start);//40 } }
javassist实现:
import javassist.ClassPool; import javassist.CtClass; import javassist.CtMethod; import javassist.Modifier; import javassist.bytecode.CodeAttribute; import javassist.bytecode.LocalVariableAttribute; import javassist.bytecode.MethodInfo; /** * * @author <a href="mailto:yankai913@gmail.com">yankai</a> * @date 2013-7-17 */ public class JavassistTool { // <ClassLoader, ClassPool> static final Map<ClassLoader, ClassPool> pool2map = new ConcurrentHashMap<ClassLoader, ClassPool>(); public static String[] getMethodParamNames(Method method) throws Exception { Class<?> clazz = method.getDeclaringClass(); String methodName = method.getName(); ClassPool pool = ClassPool.getDefault(); CtClass cc = null; try { cc = pool.get(clazz.getName()); } catch (Exception e) { if (e instanceof NotFoundException) { pool = pool2map.get(clazz.getClassLoader()); if (pool == null) { pool = new ClassPool(true); pool.appendClassPath(new LoaderClassPath(clazz.getClassLoader())); pool2map.put(clazz.getClassLoader(), pool); } } } cc = pool.get(clazz.getName()); CtMethod cm = cc.getDeclaredMethod(methodName); MethodInfo methodInfo = cm.getMethodInfo(); CodeAttribute codeAttribute = methodInfo.getCodeAttribute(); LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute.getAttribute(LocalVariableAttribute.tag); if (attr == null) { throw new IllegalStateException("LocalVariableAttribute is null"); } String[] paramNames = new String[cm.getParameterTypes().length]; int offset = Modifier.isStatic(cm.getModifiers()) ? 0 : 1; for (int i = 0; i < paramNames.length; i++) { paramNames[i] = attr.variableName(i + offset); } return paramNames; } }
javassist测试:
import java.util.Arrays; /** * * @author <a href="mailto:yankai913@gmail.com">yankai</a> * @date 2013-7-17 */ public class TestJavassist { public static void main(String[] args) throws Exception { long start = System.currentTimeMillis(); String[] paramNames = JavassistTool.getMethodParamNames(User.class, "newInstance"); System.out.println(Arrays.toString(paramNames)); System.out.println(System.currentTimeMillis() - start);//90 } }