这篇博客介绍了Java中的动态代理实现原理，包括静态代理和动态代理的示例，详细解析了Proxy.newProxyInstance方法的内部流程。同时，回顾了Java反射和注解的基本用法。最后，通过一个实战案例展示了如何利用注解、反射和动态代理实现IOC框架ButterKnife，详细解释了注入布局、成员变量和事件的处理过程。
20210702 - 架构 - IOC动态代理实现原理
1、生成代理类class
public interface HelloInterface {
void sayHello();
}
public static void main(String[] args) throws Exception {
// 生成一个class二进制文件
byte[] bytes = ProxyGenerator.generateProxyClass("DavidHelloImpl", new Class[]{HelloInterface.class});
// 输出二进制文件
File file = new File("输出路径/DavidHelloImpl.class");
FileOutputStream outputStream = new FileOutputStream(file);
outputStream.write(bytes);
outputStream.flush();
outputStream.close();
}
2、静态代理demo
public class HelloProxy implements HelloInterface {
private final HelloInterface helloInterface = new Hello();
@Override
public void sayHello() {
System.out.println("Before invoke sayHello");
helloInterface.sayHello();
System.out.println("After invoke sayHello");
}
}
public static void main(String[] args) {
HelloProxy proxy = new HelloProxy();
proxy.sayHello();
}
3、动态代理demo
public static void main(String[] args) {
// 被代理者
Hello hello = new Hello();
// 代理
HelloInterface proxy = (HelloInterface) Proxy.newProxyInstance(
hello.getClass().getClassLoader(),
hello.getClass().getInterfaces(),
new ProxyHandler(hello)// 持有被代理者引用
);
proxy.sayHello();
}
// 代理处理器
static class ProxyHandler implements InvocationHandler {
private final Object object;
public ProxyHandler(Object object) {
this.object = object;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("Before invoke " + method.getName());
Object ob = method.invoke(object, args);
System.out.println("After invoke " + method.getName());
return ob;
}
}
// 控制台输出如下：
// Before invoke sayHello
// sayHello
// After invoke sayHello
Proxy.newProxyInstance 方法内部做了三件事：
- ProxyGenerator.generateProxyClass 方法生成了一个class
- 加载这个class
- 实例化对象
4、java反射回顾
package com.watayouxiang.myjava.reflect;
public class Person {
private String name;
public Person(String name) {
super();
this.name = name;
}
private void say(String txt) {
System.out.println(txt);
}
}
// 获取字节码
Class personClazz = Class.forName("com.watayouxiang.android.java.reflect.Person");
// 获取构造函数，并实例化对象
Constructor personConstructor = personClazz.getConstructor(String.class);
Object person = personConstructor.newInstance("wata");
// 获取私有字段 name
Field nameField = personClazz.getDeclaredField("name");
nameField.setAccessible(true);
Object name = nameField.get(person);
// 调用有参私有方法
Method sayMethod = personClazz.getDeclaredMethod("say", String.class);
sayMethod.setAccessible(true);
sayMethod.invoke(person, "新年快乐~");
5、java注解回顾
- @Retention - 标识这个注解怎么保存，是只在代码中，还是编入class文件中，或者是在运行时可以通过反射访问
- @Target - 标记这个注解应该是哪种 Java 成员
6、IOC实现butterknife实战
IOC 实现：注入布局、注入成员变量、注入"点击事件/长按事件"
注解+反射+动态代理 实现 butterknife
1）使用示例
@InjectLayout(R.layout.activity_main)
public class MainActivity extends BaseActivity {
@InjectView(R.id.text)
TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
InjectManager.inject(this);
}
@OnClick({R.id.btn, R.id.text})
public void testClick(View view) {
Toast.makeText(this, "单击", Toast.LENGTH_SHORT).show();
}
@OnLongClick({R.id.btn, R.id.text})
public boolean testLongClick(View v) {
Toast.makeText(this, "长按", Toast.LENGTH_SHORT).show();
return true;
}
}
2）申明注解
@OnClick、@OnLongClick、@ViewInject、@ContentView
// --------------------------- InjectEvent
@Target(ElementType.ANNOTATION_TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface InjectEvent {
//事件三要素
//1、setOnClickListener
//2、View.onClickListener
//3、onClick
String listenerSetter();
Class<?> listenerType();
String callbackMethod();
}
// --------------------------- OnClick
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@InjectEvent(listenerSetter = "setOnClickListener",
listenerType = View.OnClickListener.class,
callbackMethod = "onClick")
public @interface OnClick {
int[] value();
}
// --------------------------- OnLongClick
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@InjectEvent(listenerSetter = "setOnLongClickListener",
listenerType = View.OnLongClickListener.class,
callbackMethod = "onLongClick")
public @interface OnLongClick {
int[] value() default -1;
}
// --------------------------- InjectLayout
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface InjectLayout {
int value();
}
// --------------------------- InjectView
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface InjectView {
int value();
}
3）实现注解功能
注解+反射+动态代理 实现 butterknife
public class InjectManager {
public static void inject(Object obj) {
// 布局注入
injectLayout(obj);
// 控件注入
injectViews(obj);
// 事件注入
injectEvent(obj);
}
private static void injectEvent(final Object obj) {
Class<?> clazz = obj.getClass();
// 获取类中的所有方法
Method[] methods = clazz.getDeclaredMethods();
for (final Method method : methods) {
// 获取方法中的所有注解如：@OnClick, @OnLongClick, @Override...
Annotation[] annotations = method.getAnnotations();
for (Annotation annotation : annotations) {
// 只获取 @InjectEvent 类型的注解
Class<? extends Annotation> annotationType = annotation.annotationType();
InjectEvent injectEvent = annotationType.getAnnotation(InjectEvent.class);
if (injectEvent == null) continue;
// 获取 @InjectEvent 注解的事件三要素
String listenerSetter = injectEvent.listenerSetter();// "setOnClickListener"
Class<?> listenerType = injectEvent.listenerType();// View.onClickListener.class
String callbackMethod = injectEvent.callbackMethod();// "onClick"
// --------------------------------------------------------
try {
// 获取 @InjectEvent 注解的 value 方法
// 通过调用该方法，从而拿到 viewIds
Method valueMethod = annotationType.getDeclaredMethod("value");
int[] viewIds = (int[]) valueMethod.invoke(annotation);
if (viewIds == null) continue;
for (int id : viewIds) {
// 通过 View view = findViewById(R.id.my_view) 方法，拿到 view 对象
Method findViewById = clazz.getMethod("findViewById", int.class);
View view = (View) findViewById.invoke(obj, id);
if (view == null) continue;
// 拿到 View 的 setOnClickListener(View.onClickListener l) 方法
Method setterMethod = view.getClass().getMethod(listenerSetter, listenerType);
// 动态代理
Object proxy = Proxy.newProxyInstance(
// ClassLoader loader
listenerType.getClassLoader(),
// Class<?>[] interfaces
new Class[]{listenerType},
// InvocationHandler h
new InvocationHandler() {
@Override
public Object invoke(Object _proxy, Method _method, Object[] args)
throws Throwable {
return method.invoke(obj, args);
}
}
);
// 调用 View 的 setOnClickListener(View.onClickListener l) 方法
setterMethod.invoke(view, proxy);
}
} catch (Exception e) {
e.printStackTrace();
}
// --------------------------------------------------------
}
}
}
private static void injectViews(Object obj) {
Class<?> clazz = obj.getClass();
Field[] fields = clazz.getDeclaredFields();
for (Field field : fields) {
InjectView injectView = field.getAnnotation(InjectView.class);
if (injectView != null) {
try {
// TextView textView = findViewById(R.id.text);
Method method = clazz.getMethod("findViewById", int.class);
int viewId = injectView.value();
View view = (View) method.invoke(obj, viewId);
field.setAccessible(true);
field.set(obj, view);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
private static void injectLayout(Object obj) {
Class<?> clazz = obj.getClass();
InjectLayout injectLayout = clazz.getAnnotation(InjectLayout.class);
if (injectLayout != null) {
// setContentView(R.layout.activity_main);
try {
Method method = clazz.getMethod("setContentView", int.class);
int value = injectLayout.value();
method.invoke(obj, value);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
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