Java Reflect一些方法介绍

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1. URLClassLoader

正常的ClassLoader,只能加载环境变量中的Class。即生成到默认的目录中的Class。

如果Class在单独的文件夹下,则需要使用URLClassLoader来加载。

URLClassLoader既可以加载网络的也可以加载本地的。

URL[] urls = new URL[] {new URL("file:/" + classOut)};
URLClassLoader urlClassLoader = new URLClassLoader(urls);
Class clz = urlClassLoader.loadClass("com.outman.example.proxy.ProxyTest");
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2. Constructor相关

利用Class中的getConstructor可以获取到Constructor对象,通过newInstance()即可创建对象。

getConstructor()获取无参数的构造函数对象

getConstructor(Class<?>... parameterTypes)获取带参数的构造函数对象,参数类型必须完成一致。如果参数类型定义的是接口类型,则此处也应该使用接口类型。

3. Class中getDeclaredMethods()和getMethods()区别

getDeclaredMethods : 简单的说,就是返回当前对象的所有方法,包括private、protected、public,但不包括继承和实现父类或父接口的。

/**
     *
     * Returns an array containing {@code Method} objects reflecting all the
     * declared methods of the class or interface represented by this {@code
     * Class} object, including public, protected, default (package)
     * access, and private methods, but excluding inherited methods.
     *
     * <p> If this {@code Class} object represents a type that has multiple
     * declared methods with the same name and parameter types, but different
     * return types, then the returned array has a {@code Method} object for
     * each such method.
     *
     * <p> If this {@code Class} object represents a type that has a class
     * initialization method {@code <clinit>}, then the returned array does
     * <em>not</em> have a corresponding {@code Method} object.
     *
     * <p> If this {@code Class} object represents a class or interface with no
     * declared methods, then the returned array has length 0.
     *
     * <p> If this {@code Class} object represents an array type, a primitive
     * type, or void, then the returned array has length 0.
     *
     * <p> The elements in the returned array are not sorted and are not in any
     * particular order.
     *
     * @return  the array of {@code Method} objects representing all the
     *          declared methods of this class
     * @throws  SecurityException
     *          If a security manager, <i>s</i>, is present and any of the
     *          following conditions is met:
     *
     *          <ul>
     *
     *          <li> the caller's class loader is not the same as the
     *          class loader of this class and invocation of
     *          {@link SecurityManager#checkPermission
     *          s.checkPermission} method with
     *          {@code RuntimePermission("accessDeclaredMembers")}
     *          denies access to the declared methods within this class
     *
     *          <li> the caller's class loader is not the same as or an
     *          ancestor of the class loader for the current class and
     *          invocation of {@link SecurityManager#checkPackageAccess
     *          s.checkPackageAccess()} denies access to the package
     *          of this class
     *
     *          </ul>
     *
     * @jls 8.2 Class Members
     * @jls 8.4 Method Declarations
     * @since JDK1.1
     */
    @CallerSensitive
    public Method[] getDeclaredMethods() throws SecurityException {
        checkMemberAccess(Member.DECLARED, Reflection.getCallerClass(), true);
        return copyMethods(privateGetDeclaredMethods(false));
    }
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getMethods : 简单的说,就是返回所有public的方法,不止自己的,还包括父类和父接口的。

/**
     * Returns an array containing {@code Method} objects reflecting all the
     * public methods of the class or interface represented by this {@code
     * Class} object, including those declared by the class or interface and
     * those inherited from superclasses and superinterfaces.
     *
     * <p> If this {@code Class} object represents a type that has multiple
     * public methods with the same name and parameter types, but different
     * return types, then the returned array has a {@code Method} object for
     * each such method.
     *
     * <p> If this {@code Class} object represents a type with a class
     * initialization method {@code <clinit>}, then the returned array does
     * <em>not</em> have a corresponding {@code Method} object.
     *
     * <p> If this {@code Class} object represents an array type, then the
     * returned array has a {@code Method} object for each of the public
     * methods inherited by the array type from {@code Object}. It does not
     * contain a {@code Method} object for {@code clone()}.
     *
     * <p> If this {@code Class} object represents an interface then the
     * returned array does not contain any implicitly declared methods from
     * {@code Object}. Therefore, if no methods are explicitly declared in
     * this interface or any of its superinterfaces then the returned array
     * has length 0. (Note that a {@code Class} object which represents a class
     * always has public methods, inherited from {@code Object}.)
     *
     * <p> If this {@code Class} object represents a primitive type or void,
     * then the returned array has length 0.
     *
     * <p> Static methods declared in superinterfaces of the class or interface
     * represented by this {@code Class} object are not considered members of
     * the class or interface.
     *
     * <p> The elements in the returned array are not sorted and are not in any
     * particular order.
     *
     * @return the array of {@code Method} objects representing the
     *         public methods of this class
     * @throws SecurityException
     *         If a security manager, <i>s</i>, is present and
     *         the caller's class loader is not the same as or an
     *         ancestor of the class loader for the current class and
     *         invocation of {@link SecurityManager#checkPackageAccess
     *         s.checkPackageAccess()} denies access to the package
     *         of this class.
     *
     * @jls 8.2 Class Members
     * @jls 8.4 Method Declarations
     * @since JDK1.1
     */
    @CallerSensitive
    public Method[] getMethods() throws SecurityException {
        checkMemberAccess(Member.PUBLIC, Reflection.getCallerClass(), true);
        return copyMethods(privateGetPublicMethods());
    }
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下面通过简单的代码来看下

public class Product implements IProduct {

    @Override
    public void produce() {

    }
}
public class ChildProduct extends Product {

    public ChildProduct() {

    }
    public void log() {

    }
    private void get() {

    }
}
public class Main {

    public static void main(String[] args) {

        Product childProduct = new ChildProduct();
        Method[] decMethods = childProduct.getClass().getDeclaredMethods();
        System.out.println("getDeclaredMethods...");
        for (Method m : decMethods) {
            System.out.println(m.toGenericString());
        }
        Method[] methods = childProduct.getClass().getMethods();
        System.out.println("getMethods...");
        for (Method m : methods) {
            System.out.println(m.toGenericString());
        }
    }
}
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输出结果如下

getDeclaredMethods...
private void com.outman.example.proxy.ChildProduct.get()
public void com.outman.example.proxy.ChildProduct.log()

getMethods...
public void com.outman.example.proxy.ChildProduct.log()
public void com.outman.example.proxy.Product.produce()
public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
public final void java.lang.Object.wait() throws java.lang.InterruptedException
public boolean java.lang.Object.equals(java.lang.Object)
public java.lang.String java.lang.Object.toString()
public native int java.lang.Object.hashCode()
public final native java.lang.Class<?> java.lang.Object.getClass()
public final native void java.lang.Object.notify()
public final native void java.lang.Object.notifyAll()
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