Shulou(Shulou.com)06/02 Report--

It is believed that many inexperienced people have no idea about how to analyze the reflection mechanism Reflection in Java. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

1. Get the properties of an object

Java instance

Public Object getProperty (Object owner, String fieldName) throws Exception {Class ownerownerClass = owner.getClass (); Field field = ownerClass.getField (fieldName) Object property = field.get (owner) Return property;}

Class ownerClass = owner.getClass (): get the Class of the object.

Field field = ownerClass.getField (fieldName): get the properties declared by the class through Class.

Object property = field.get (owner): get an instance of this property through the object. If the attribute is non-public, IllegalAccessException will be reported here.

two。 Get the static properties of a class

Public Object getStaticProperty (String className, String fieldName) throws Exception {Class ownerClass = Class.forName (className); Field field = ownerClass.getField (fieldName) Object property = field.get (ownerClass); return property }

Class ownerClass = Class.forName (className): first get the Class of this class.

Field field = ownerClass.getField (fieldName): as above, get the properties declared by the class through Class.

Object property = field.get (ownerClass): this is a little different from the above, because this property is static, so it is taken directly from the Class of the class.

3. A method that executes an object

Public Object invokeMethod (Object owner, String methodName, Object [] args) throws Exception {Class ownerownerClass = owner.getClass (); Class [] argsClass = new Class [args.length]; for (int I = 0, j = args.length; I < j; iClass +) {argsClass [I] = args [I] .getClass ();} Method method = ownerClass.getMethod (methodName, argsClass) Return method.invoke (owner, args);}

Class owner_class = owner.getClass (): first of all, you must get the Class of this object.

Line 3: 6: configure the Class array of parameters as a condition for finding Method.

Method method = ownerClass.getMethod (methodName, argsClass): get the Method to be executed through the Class array of Method names and parameters.

Method.invoke (owner, args): the parameters that execute the Method,invoke method are the objects that execute the method, and the array of parameters. The return value is Object, which is also the return value of the method.

4. Execute the static method of a class

Public Object invokeStaticMethod (String className, String methodName, Object [] args) throws Exception {Class ownerClass = Class.forName (className) Class [] argsClass = new Class [args.length] For (int I = 0, j = args.length; I < j; iClass +) {argsClass [I] = args [I] .getClass () } Method method = ownerClass.getMethod (methodName, argsClass) Return method.invoke (null, args);}

The basic principle is the same as example 3, except for * one line. One parameter of invoke is null, because this is a static method and does not need to be run with an instance.

5. Create a new Java instance

Public Object newInstance (String className, Object [] args) throws Exception {Class newoneClass = Class.forName (className); Class [] argsClass = new Class [args.length] For (int I = 0, j = args.length; I < j; iClass +) {argsClass [I] = args [I] .getClass () } Constructor cons = newoneClass.getConstructor (argsClass) Return cons.newInstance (args);}

The method here is a method that executes a constructor with parameters to create a new instance. If you don't need parameters, you can directly use newoneClass.newInstance () to do so.

Class newoneClass = Class.forName (className): * * step to get the Class of the instance to be constructed.

Lines 6-10: get the Class array of parameters.

Constructor cons = newoneClass.getConstructor (argsClass): get the constructor.

Cons.newInstance (args): create a new instance.

6. Determine whether it is a Java instance of a class

Public boolean isInstance (Object obj, Class cls) {return cls.isInstance (obj);}

7. Get an element in the array

Public Object getByArray (Object array, int index) {return Array.get (array,index);}

Complete source code is attached:

Import java.lang.reflect.Array; import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.Method / * Java Reflection Cookbook * * @ author Michael Lee * @ since 2006-8-23 * @ version 0.1a * / public class Reflection {/ * get the public property of an object * * @ param owner FieldName * @ return this attribute object * @ throws Exception * * / public Object getProperty (Object owner, String fieldName) throws Exception {Class ownerownerClass = owner.getClass () Field field = ownerClass.getField (fieldName); Object property = field.get (owner); return property } / * get the static public property of a class * * @ param className class name * @ param fieldName property name * @ return the attribute object * @ throws Exception * / public Object getStaticProperty (String className String fieldName) throws Exception {Class ownerClass = Class.forName (className) Field field = ownerClass.getField (fieldName); Object property = field.get (ownerClass); return property } / * execute an object method * * @ param owner * object * @ param methodName * method name * @ param args * parameter * @ The return method returns a value of * @ throws Exception * / public Object invokeMethod (Object owner String methodName, Object [] args) throws Exception {Class ownerownerClass = owner.getClass () Class [] argsClass = new Class [args.length]; for (int I = 0, j = args.length; I < j; iClass +) {argsClass [I] = args [I] .getClass ();} Method method = ownerClass.getMethod (methodName, argsClass); return method.invoke (owner, args) } / * execute a static method of a class * * @ param className * class name * @ param methodName * method name * @ param args * parameter array * @ return results returned by the execution method * @ throws Exception * / public Object invokeStaticMethod (String className String methodName, Object [] args) throws Exception {Class ownerClass = Class.forName (className) Class [] argsClass = new Class [args.length]; for (int I = 0, j = args.length; I < j; iClass +) {argsClass [I] = args [I] .getClass ();} Method method = ownerClass.getMethod (methodName, argsClass); return method.invoke (null, args) } / * New instance * * @ param className * Class name * @ param args * Constructor parameter * @ return newly created instance * @ throws Exception * / public Object newInstance (String className Object [] args) throws Exception {Class newoneClass = Class.forName (className) Class [] argsClass = new Class [args.length]; for (int I = 0, j = args.length; I < j; iClass +) {argsClass [I] = args [I] .getClass ();} Constructor cons = newoneClass.getConstructor (argsClass); return cons.newInstance (args) } / * * is it an instance of a class * @ param obj instance * @ param cls class * @ return if obj is an instance of this class, return true * / public boolean isInstance (Object obj, Class cls) {return cls.isInstance (obj) } / * get an element in the array * @ param array array * @ param index index * @ return returns the value of the index component in the specified array object * / public Object getByArray (Object array, int index) {return Array.get (array,index) } after reading the above, have you mastered how to parse the reflection mechanism Reflection in Java? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.