定义：Reflection是java开发语言特性之一，它允许运行中的java程序对自身进行检测，自审，并能操作程序内部的属性和方法，Reflection是java被视为动态语言关键之一。允许程序从执行期的Reflection APIS取得任何已知名称的class内部信息，包含packages、type parameters、superclass、implement Interfaces、inner classes、outer class、fields、methods、constructors、modifiers，并可在执行期间执行instance，更变field内容，唤醒method。
反射过程中常用的类： java反射所需要的类并不多，他们分别是：Class、Constructor、Object、Method、Field。 Class类：每个class都有一个相应的Class对象。也就是说，当我们编写一个类，编译完成后，在生成的.class文件中，就会产生一个Class对象，在运行期间如果我们需要产生某个类的对象，JVM就会检测该类型的Class对象是否已经被加载，如果没有被加载，则虚拟机会根据类名称找到并加载相对应的.class文件，一旦某个类型的Class对象加载到内存中，就可以用它来产生相应的对象。 Constructor类：封装了反射类的构造方法，提供该类单个构造方法和访问权限信息。 Object类：每个类都使用Object作为超类，所有的对象都实现这个类的方法。 Method类：提供有关类或者接口单独某个方法的信息，以及动态访问权限，所反映的方法可能是类方法或者实例方法以及抽象方法。 Field类：提供有关类或者结构单独属性的信息，以及动态访问权限，所反映的属性可能是类属性或者实例属性。
项目中的实际运用： 上次在讲述Android AIDL IPC通信的时候提到过，基于AIDL实现客户端被注册的view通过反射以及服务端传过来的数据达成一个交互过程。实现图片文字的显示过程。
客户端调用： 首先：我们需要实现我们要注册的MyImageView，继承自ImageView，主要用来图片显示。
package com.zlc.aidl.client;
import android.content.Context;
import android.graphics.Bitmap;
import android.widget.ImageView;
public class MyImageView extends ImageView{
public MyImageView(Context context) {
super(context);
}
@Override
public void setImageBitmap(Bitmap bm) {
// TODO Auto-generated method stub
super.setImageBitmap(bm);
}
}
package com.zlc.aidl.client;
import android.content.Context;
import android.graphics.Bitmap;
import android.widget.ImageView;
public class MyImageView extends ImageView{
public MyImageView(Context context) {
super(context);
}
@Override
public void setImageBitmap(Bitmap bm) {
// TODO Auto-generated method stub
super.setImageBitmap(bm);
}
}然后：我们需要反射的工具类ReflectionInvoke.java，用来反射调用注册view对象里面的方法，通过服务端传过来的参数和对应方法名来进行反射调用。在工具类中包含一个InvokeKey的内部类，主要用来标示一个对象的某个方法，并保存到工具类集合里面，下次调用的时候不需要再进行寻找method的过程，直接invoke反射调用就行。
package com.zlc.aidl.client;
import java.lang.ref.WeakReference;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.List;
import android.util.Log;
public class ReflectionInvoke {
public static HashMap<InvokeKey, WeakReference<ReflectionInvoke>> reflections = new HashMap<ReflectionInvoke.InvokeKey, WeakReference<ReflectionInvoke>>();
private Method method;
private Class<?> clazz;
private Class<?> parameterClasses[];
static class InvokeKey {
String className;
String methodName;
String[] paramsClassName;
public InvokeKey(String className, String methodName, String[] paramsClassName) {
this.className = className;
this.methodName = methodName;
this.paramsClassName = paramsClassName;
}
@Override
public int hashCode() {
// TODO Auto-generated method stub
int ret = className.hashCode();
ret = methodName.hashCode() + ret * 10;
for (int i = 0; i < paramsClassName.length; i++) {
ret = paramsClassName[i].hashCode() + ret * 10;
}
return ret;
}
@Override
public boolean equals(Object o) {
if (o instanceof InvokeKey) {
InvokeKey key = (InvokeKey) o;
if (!key.className.equals(className) || !key.methodName.equals(methodName)
|| key.paramsClassName.length != paramsClassName.length) {
return false;
} else {
for (int i = 0; i < paramsClassName.length; i++) {
if (!key.paramsClassName[i].equals(paramsClassName[i]))
return false;
}
return true;
}
}
return false;
}
}
Class<?> classForNameX(String name) throws Exception {
if ("int".equals(name))
return int.class;
else if ("char".equals(name))
return char.class;
else if ("short".equals(name))
return short.class;
else if ("byte".equals(name))
return byte.class;
else if ("long".equals(name))
return long.class;
else if ("float".equals(name))
return float.class;
else if ("double".equals(name))
return double.class;
else if ("boolean".equals(name))
return boolean.class;
return Class.forName(name);
}
private ReflectionInvoke(InvokeKey key) throws Exception {
clazz = Class.forName(key.className);
parameterClasses = new Class[key.paramsClassName.length];
for (int i = 0; i < parameterClasses.length; i++) {
parameterClasses[i] = classForNameX(key.paramsClassName[i]);
}
method = clazz.getMethod(key.methodName, parameterClasses);
}
public static ReflectionInvoke getInvoker(String className, String methodName,
List<String> argsClassName) {
String[] arrayarges = new String[argsClassName.size()];
argsClassName.toArray(arrayarges);
return getInvoker(className, methodName, arrayarges);
}
public static ReflectionInvoke getInvoker(String className, String methodName, String... args) {
ReflectionInvoke invoke = null;
synchronized (reflections) {
try {
InvokeKey key = new InvokeKey(className, methodName, args);
WeakReference<ReflectionInvoke> w = reflections.get(key);
if (w == null ? true : (invoke = w.get()) == null) {
invoke = new ReflectionInvoke(key);
reflections.put(key, new WeakReference<ReflectionInvoke>(invoke));
}
} catch (Exception e) {
e.printStackTrace();
}
}
return invoke;
}
public Object invokeNoException(Object obj, Object... args) {
try {
return method.invoke(obj, args);
} catch (Exception e) {
Log.d("Exception", "invoke error");
}
return null;
}
public Object invoke(Object obj, Object... args) throws IllegalArgumentException,
IllegalAccessException, InvocationTargetException {
Log.d("ReflectionInvoke", "invoke invoke invoke");
return method.invoke(obj, args);
}
}
package com.zlc.aidl.client;
import java.lang.ref.WeakReference;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.List;
import android.util.Log;
public class ReflectionInvoke {
public static HashMap<InvokeKey, WeakReference<ReflectionInvoke>> reflections = new HashMap<ReflectionInvoke.InvokeKey, WeakReference<ReflectionInvoke>>();
private Method method;
private Class<?> clazz;
private Class<?> parameterClasses[];
static class InvokeKey {
String className;
String methodName;
String[] paramsClassName;
public InvokeKey(String className, String methodName, String[] paramsClassName) {
this.className = className;
this.methodName = methodName;
this.paramsClassName = paramsClassName;
}
@Override
public int hashCode() {
// TODO Auto-generated method stub
int ret = className.hashCode();
ret = methodName.hashCode() + ret * 10;
for (int i = 0; i < paramsClassName.length; i++) {
ret = paramsClassName[i].hashCode() + ret * 10;
}
return ret;
}
@Override
public boolean equals(Object o) {
if (o instanceof InvokeKey) {
InvokeKey key = (InvokeKey) o;
if (!key.className.equals(className) || !key.methodName.equals(methodName)
|| key.paramsClassName.length != paramsClassName.length) {
return false;
} else {
for (int i = 0; i < paramsClassName.length; i++) {
if (!key.paramsClassName[i].equals(paramsClassName[i]))
return false;
}
return true;
}
}
return false;
}
}
Class<?> classForNameX(String name) throws Exception {
if ("int".equals(name))
return int.class;
else if ("char".equals(name))
return char.class;
else if ("short".equals(name))
return short.class;
else if ("byte".equals(name))
return byte.class;
else if ("long".equals(name))
return long.class;
else if ("float".equals(name))
return float.class;
else if ("double".equals(name))
return double.class;
else if ("boolean".equals(name))
return boolean.class;
return Class.forName(name);
}
private ReflectionInvoke(InvokeKey key) throws Exception {
clazz = Class.forName(key.className);
parameterClasses = new Class[key.paramsClassName.length];
for (int i = 0; i < parameterClasses.length; i++) {
parameterClasses[i] = classForNameX(key.paramsClassName[i]);
}
method = clazz.getMethod(key.methodName, parameterClasses);
}
public static ReflectionInvoke getInvoker(String className, String methodName,
List<String> argsClassName) {
String[] arrayarges = new String[argsClassName.size()];
argsClassName.toArray(arrayarges);
return getInvoker(className, methodName, arrayarges);
}
public static ReflectionInvoke getInvoker(String className, String methodName, String... args) {
ReflectionInvoke invoke = null;
synchronized (reflections) {
try {
InvokeKey key = new InvokeKey(className, methodName, args);
WeakReference<ReflectionInvoke> w = reflections.get(key);
if (w == null ? true : (invoke = w.get()) == null) {
invoke = new ReflectionInvoke(key);
reflections.put(key, new WeakReference<ReflectionInvoke>(invoke));
}
} catch (Exception e) {
e.printStackTrace();
}
}
return invoke;
}
public Object invokeNoException(Object obj, Object... args) {
try {
return method.invoke(obj, args);
} catch (Exception e) {
Log.d("Exception", "invoke error");
}
return null;
}
public Object invoke(Object obj, Object... args) throws IllegalArgumentException,
IllegalAccessException, InvocationTargetException {
Log.d("ReflectionInvoke", "invoke invoke invoke");
return method.invoke(obj, args);
}
}其次：需要准备一个实现parcelable的对象，用来在两个进程之间传递方法名、方法参数等信息。
package com.zlc.aidl;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import android.graphics.Bitmap;
import android.os.Parcel;
import android.os.ParcelFileDescriptor;
import android.os.Parcelable;
public class JsonReflectionInvokParcelable implements Parcelable{
public String objectId;
public String methodname;
public List<String> argsClassName;
public List<Object> argsVaule;
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(objectId);
dest.writeString(methodname);
dest.writeList(argsClassName);
dest.writeList(argsVaule);
}
public static final Parcelable.Creator<JsonReflectionInvokParcelable> CREATOR = new Parcelable.Creator<JsonReflectionInvokParcelable>() {
public JsonReflectionInvokParcelable createFromParcel(Parcel in) {
JsonReflectionInvokParcelable tp = new JsonReflectionInvokParcelable();
tp.objectId = in.readString();
tp.methodname = in.readString();
tp.argsClassName = new ArrayList<String>();
in.readList(tp.argsClassName, null);
tp.argsVaule = new ArrayList<Object>();
in.readList(tp.argsVaule, null);
return tp;
}
public JsonReflectionInvokParcelable[] newArray(int size) {
return new JsonReflectionInvokParcelable[size];
}
};
public void clean() {
for (Object o : argsVaule) {
try {
if (o instanceof ParcelFileDescriptor)
((ParcelFileDescriptor) o).close();
else if (o instanceof Bitmap)
((Bitmap) o).recycle();
} catch (IOException e) {
}
}
}
}
package com.zlc.aidl;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import android.graphics.Bitmap;
import android.os.Parcel;
import android.os.ParcelFileDescriptor;
import android.os.Parcelable;
public class JsonReflectionInvokParcelable implements Parcelable{
public String objectId;
public String methodname;
public List<String> argsClassName;
public List<Object> argsVaule;
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(objectId);
dest.writeString(methodname);
dest.writeList(argsClassName);
dest.writeList(argsVaule);
}
public static final Parcelable.Creator<JsonReflectionInvokParcelable> CREATOR = new Parcelable.Creator<JsonReflectionInvokParcelable>() {
public JsonReflectionInvokParcelable createFromParcel(Parcel in) {
JsonReflectionInvokParcelable tp = new JsonReflectionInvokParcelable();
tp.objectId = in.readString();
tp.methodname = in.readString();
tp.argsClassName = new ArrayList<String>();
in.readList(tp.argsClassName, null);
tp.argsVaule = new ArrayList<Object>();
in.readList(tp.argsVaule, null);
return tp;
}
public JsonReflectionInvokParcelable[] newArray(int size) {
return new JsonReflectionInvokParcelable[size];
}
};
public void clean() {
for (Object o : argsVaule) {
try {
if (o instanceof ParcelFileDescriptor)
((ParcelFileDescriptor) o).close();
else if (o instanceof Bitmap)
((Bitmap) o).recycle();
} catch (IOException e) {
}
}
}
}服务端调用
再次：服务端发送数据之前检测并且封装参数的类型
……
public void callReflection(String json, String objId, String method,
Object ...args) throws RemoteException {
JsonReflectionInvokParcelable p = new JsonReflectionInvokParcelable();
p.objectId = objId;
p.methodname = method;
p.argsClassName = new ArrayList<String>();
p.argsVaule = new ArrayList<Object>();
Log.d(TAG, "callReflection222 json=" + json);
for (int i = 0; i < args.length; i++) {
Object o = args[i];
@SuppressWarnings("rawtypes")
Class clazz = o.getClass();
if (clazz.isPrimitive() || o instanceof Parcelable || o instanceof String
|| o instanceof Integer || o instanceof Short || o instanceof Float
|| o instanceof Double || o instanceof Character) {
p.argsClassName.add(clazz.getCanonicalName());
p.argsVaule.add(o);
} else {
throw new RuntimeException("args only support primitives and String");
}
}
callback.onReflectionCallback(p, json);
Log.d(TAG, "callReflection222 end json=" + json);
}
……
……
public void callReflection(String json, String objId, String method,
Object ...args) throws RemoteException {
JsonReflectionInvokParcelable p = new JsonReflectionInvokParcelable();
p.objectId = objId;
p.methodname = method;
p.argsClassName = new ArrayList<String>();
p.argsVaule = new ArrayList<Object>();
Log.d(TAG, "callReflection222 json=" + json);
for (int i = 0; i < args.length; i++) {
Object o = args[i];
@SuppressWarnings("rawtypes")
Class clazz = o.getClass();
if (clazz.isPrimitive() || o instanceof Parcelable || o instanceof String
|| o instanceof Integer || o instanceof Short || o instanceof Float
|| o instanceof Double || o instanceof Character) {
p.argsClassName.add(clazz.getCanonicalName());
p.argsVaule.add(o);
} else {
throw new RuntimeException("args only support primitives and String");
}
}
callback.onReflectionCallback(p, json);
Log.d(TAG, "callReflection222 end json=" + json);
}
……最后：从服务端调用客户端注册view的某个指定方法
private final IMyAidlService.Stub mBinder = new IMyAidlService.Stub() {
@Override
public void registerClient(AIDLCallback cb) throws RemoteException {
Log.d(TAG, "registerClient");
callback = cb;
Bitmap bmp = BitmapFactory.decodeFile("/data/data/com.zlc.aidl.server/files/1.jpg");
callReflection("just for test","myImageView","setImageBitmap",bmp);
cb.asBinder().linkToDeath(new DeathRecipient() {
@Override
public void binderDied() {
// TODO Auto-generated method stub
try {
Log.i(TAG, "[ServiceAIDLImpl]binderDied.");
} catch (Throwable e) {
}
}
}, 0);
}
};
private final IMyAidlService.Stub mBinder = new IMyAidlService.Stub() {
@Override
public void registerClient(AIDLCallback cb) throws RemoteException {
Log.d(TAG, "registerClient");
callback = cb;
Bitmap bmp = BitmapFactory.decodeFile("/data/data/com.zlc.aidl.server/files/1.jpg");
callReflection("just for test","myImageView","setImageBitmap",bmp);
cb.asBinder().linkToDeath(new DeathRecipient() {
@Override
public void binderDied() {
// TODO Auto-generated method stub
try {
Log.i(TAG, "[ServiceAIDLImpl]binderDied.");
} catch (Throwable e) {
}
}
}, 0);
}
};具体反射的其他一些用途和使用方式，大家可以去问问度娘和谷哥，这有个例子讲述了大部分使用方法。
最后附上反射使用实例的源码，图片自己下载一张存放到/data/data/com.zlc.aidl.server/files/目录下，如果没有files目录，可通过代码创建或者通过linux命令创建。
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