反射还能这么玩？

其实本来想加个前缀，结果标题是《Android 中反射还能这么用？》，后来想想，也不恰当，就把Android去了，本身反射是Java的东西，你硬生生的加个Android显然是不恰当的。

这几天稍微过了一下Weex的源码，可谓是亲眼目睹了它的源码。无意间发现一个类，叫WXHack，搜索一下代码，发现在Weex里用的地方就一处，好奇心驱使下去看了WXHack的源码，好家伙！看完之后总觉得这个类似曾相识，后来昨天在看OpenAtlas的代码的时候又看到了这个类，相关链接如下

Hack.java

Interception.java

后来我断定这个类应该是淘宝Atlas里的类，Weex直接抽出来了。为了验证自己的想法，下了个淘宝客户端反编译了下去找这个类，真的找到了。



想看源码的可以直接点上面的链接去看OpenAtals里的类，也可以看这个保持了淘宝的包结构，但是反编译并完全的项目，也就是包含了一些字节码的，但是这两个类应该是完整的。

AtlasForAndroid

那么携程的动态加载框架也算是有Atlas的成分了，自然也就有这两个类了,不出所料的找到了它们。

Hack.java

Interception.java

其实这个应该也不是淘专的专利，因为后来我在github上搜索了一番，发现了几个类似的类，这几个类在eclipse中竟然出现了。

HackedField.java

HackedMethod0.java

HackedMethod1.java

那么，这两个类到底有什么作用呢，莫慌，容我慢慢道来。

首先，从名字上可以看出这是一个Hack类，它的作用就是辅助反射，但是它们却不是简简单单的辅助反射，而是反射后包装的形式：类，方法，字段 ，也就是HackedClass,HackedConstructor,HackedMethod,HackedField这几个反射的包装形式。并且还有AssertionFailureHandler用于处理反射发生异常时的处理，你可以选择扔出异常或者自己处理掉。

在看他的源码之前，我们先来看看传统的反射是怎么玩的。

写了两三个类用来测试。

Student实体类，内部有一个IBehavior类，代表学生的行为；此外还有静态变量，非静态变量，静态方法，非静态方法，泛型变量，作用就是等下测试不同场景的反射。

scores = new HashMap();

private IBehavior behavior = new BehaviorImpl();

public Student() {
}

public Student(String name, int age) {
this.name = name;
this.age = age;
}

public IBehavior getBehavior() {
return behavior;
}

public void setBehavior(IBehavior behavior) {
this.behavior = behavior;
}

public void addScore(String name, int score) {
scores.put(name, score);
}

public HashMap getScores() {
return scores;
}

public void setScores(HashMap scores) {
this.scores = scores;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public static String getSchool() {
return school;
}

public static void setSchool(String school) {
Student.school = school;
}

public void say(String word) {
System.out.println(word);
}

@Override
public String toString() {
return "Student{" +
"school=" + school +
", age=" + age +
", name='" + name + '\'' +
", scores=" + scores +
", behavior=" + behavior +
'}';
}
}
" data-snippet-id="ext.ca8f931585b84a0209fec749c2b6697e" data-snippet-saved="false" data-codota-status="done">[code]public class Student implements Serializable {
private static String school = "清华大学";
private String name;
private int age;
private HashMap<String, Integer> scores = new HashMap<String, Integer>();

private IBehavior behavior = new BehaviorImpl();

public Student() {
}

public Student(String name, int age) {
this.name = name;
this.age = age;
}

public IBehavior getBehavior() {
return behavior;
}

public void setBehavior(IBehavior behavior) {
this.behavior = behavior;
}

public void addScore(String name, int score) {
scores.put(name, score);
}

public HashMap<String, Integer> getScores() {
return scores;
}

public void setScores(HashMap<String, Integer> scores) {
this.scores = scores;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public static String getSchool() {
return school;
}

public static void setSchool(String school) {
Student.school = school;
}

public void say(String word) {
System.out.println(word);
}

@Override
public String toString() {
return "Student{" +
"school=" + school +
", age=" + age +
", name='" + name + '\'' +
", scores=" + scores +
", behavior=" + behavior +
'}';
}
}

IBehavior接口以及其实现类的代码如下

public interface IBehavior {
void perform(String behaiviorName, String behaiviorContent);
}
public class BehaviorImpl implements IBehavior {
@Override
public void perform(String behaiviorName, String behaiviorContent) {
System.out.println("behaiviorName:" + behaiviorName);
System.out.println("behaiviorContent:" + behaiviorContent);
}
}

你要反射，就先得拿到Class对象，两种方式，一直是Class在你的项目中，可以直接引用，第二种就是这个Class可能你不能直接引用，比如Android中的ContextImpl，一般来说，第二种的使用场景会更广泛。

studentClassByClass = Student.class;

//通过class的字符串全类名
Class studentClassByName = Class.forName("cn.edu.zafu.Student");" data-snippet-id="ext.526205ef6aea7f48882bccbd81825bcb" data-snippet-saved="false" data-codota-status="done">[code]//直接通过class
Class<?> studentClassByClass = Student.class;

//通过class的字符串全类名
Class<?> studentClassByName = Class.forName("cn.edu.zafu.Student");

然后你可以直接调用class的newInstance方法新建一个对象，但是对于没有默认构造函数的类来说，你需要拿到构造函数再去新建对象。这里需要注意的是你不知道修饰符是private，protected，public中的哪一个时，建议调用setAccessible设置成true，不然极有可能会发生异常。

constructor = studentClassByName.getConstructor(String.class, int.class);
constructor.setAccessible(true);
Student student = (Student) constructor.newInstance("区长", 22);
System.out.println(student);" data-snippet-id="ext.4fa1e103a743a0644b71ec9c05ae22d3" data-snippet-saved="false" data-codota-status="done">[code]//构造函数new对象
Constructor<?> constructor = studentClassByName.getConstructor(String.class, int.class);
constructor.setAccessible(true);
Student student = (Student) constructor.newInstance("区长", 22);
System.out.println(student);

对于静态变量的访问，可以拿到Field，直接设置即可。set方法的第一个参数传null就是了。

//静态变量
Field schoolField = studentClassByName.getDeclaredField("school");
schoolField.setAccessible(true);
schoolField.set(null, "浙江大学");
System.out.println(Student.getSchool());

但是对于非静态变量，set方法的第一个参数你就需要传递一个实例进去，比如上面通过构造函数new出来的对象。

//非静态变量
Field ageFiled = studentClassByName.getDeclaredField("age");
ageFiled.setAccessible(true);
Integer age = (Integer) ageFiled.get(student);
System.out.println(age);

ageFiled.set(student, 100);
System.out.println(student.getAge());

同理静态方法同静态变量

//静态方法调用
Method setSchoolMethod = studentClassByName.getDeclaredMethod("setSchool", String.class);
setSchoolMethod.invoke(null, "清华大学");
System.out.println(Student.getSchool());

非静态方法同非静态变量

//非静态方法调用
Method sayMethod = studentClassByName.getDeclaredMethod("say", String.class);
sayMethod.setAccessible(true);
sayMethod.invoke(student, "hello world");

等等，还有一个泛型变量呢

scores = new HashMap();" data-snippet-id="ext.bedc64eb9121fe1ebb84b3c5cc452777" data-snippet-saved="false" data-codota-status="done">[code] private HashMap<String, Integer> scores = new HashMap<String, Integer>();

懵逼了，不会写。。。。。其实还是一样，强转就ok了，只不过强转前需要对类型进行校验。

然后就是异常处理，反射大多数人都是通过try catch直接捕捉异常。。。这也没什么好说的。

劫持，什么叫劫持呢，其实就是替换字段，有人说你直接反射拿到变量，直接反射替换就是了，这是一种方式，但是这并不是我想要的，比如我要劫持Student里的behavior变量，但是我不想修改它，我想保留它原来的逻辑，但是我又想加入新的东西，这个就有点类型面向切面编程了，比如日志的注入。怎么做？懵逼了。。。。显然是动态代理啊。使用代理类去完成劫持操作，既可以保留原有操作，又可以增加新的逻辑。

那么Hack类是怎么做的呢。首先生成HackedClass类，怎么生成的呢,调用Hack的into方法，入参有两种形式，一种就是直接传Class，另一种就是传递Class的全类名字符串。

HackedClass into(final Class clazz) {
return new HackedClass(clazz);
}

@SuppressWarnings({"rawtypes", "unchecked"})
public static  HackedClass into(final String class_name) throws HackDeclaration.HackAssertionException {
try {
return new HackedClass(Class.forName(class_name));
} catch (final ClassNotFoundException e) {
fail(new HackDeclaration.HackAssertionException(e));
return new HackedClass(null);    // TODO: Better solution to avoid null?
}
}" data-snippet-id="ext.5e91ff262e0e464ad898711f8fe92360" data-snippet-saved="false" data-codota-status="done">[code]public static <T> HackedClass<T> into(final Class<T> clazz) {
return new HackedClass<T>(clazz);
}

@SuppressWarnings({"rawtypes", "unchecked"})
public static <T> HackedClass<T> into(final String class_name) throws HackDeclaration.HackAssertionException {
try {
return new HackedClass(Class.forName(class_name));
} catch (final ClassNotFoundException e) {
fail(new HackDeclaration.HackAssertionException(e));
return new HackedClass(null);    // TODO: Better solution to avoid null?
}
}

into方法返回的是HackedClass对象，这个对象是对反射的包装类之一。其源码如下

{

protected Class mClass;

public HackedClass(final Class clazz) {
mClass = clazz;
}

public HackedField staticField(final String name) throws HackDeclaration.HackAssertionException {
return new HackedField(mClass, name, Modifier.STATIC);
}

public HackedField field(final String name) throws HackDeclaration.HackAssertionException {
return new HackedField(mClass, name, 0);
}

public HackedMethod staticMethod(final String name, final Class... arg_types) throws HackDeclaration.HackAssertionException {
return new HackedMethod(mClass, name, arg_types, Modifier.STATIC);
}

public HackedMethod method(final String name, final Class... arg_types) throws HackDeclaration.HackAssertionException {
return new HackedMethod(mClass, name, arg_types, 0);
}

public HackedConstructor constructor(final Class... arg_types) throws HackDeclaration.HackAssertionException {
return new HackedConstructor(mClass, arg_types);
}

public Class getmClass() {
return mClass;
}
}   " data-snippet-id="ext.64cee6afb187f4390fafb782427d0abb" data-snippet-saved="false" data-codota-status="done">[code]public static class HackedClass<C> {

protected Class<C> mClass;

public HackedClass(final Class<C> clazz) {
mClass = clazz;
}

public HackedField<C, Object> staticField(final String name) throws HackDeclaration.HackAssertionException {
return new HackedField<C, Object>(mClass, name, Modifier.STATIC);
}

public HackedField<C, Object> field(final String name) throws HackDeclaration.HackAssertionException {
return new HackedField<C, Object>(mClass, name, 0);
}

public HackedMethod staticMethod(final String name, final Class<?>... arg_types) throws HackDeclaration.HackAssertionException {
return new HackedMethod(mClass, name, arg_types, Modifier.STATIC);
}

public HackedMethod method(final String name, final Class<?>... arg_types) throws HackDeclaration.HackAssertionException {
return new HackedMethod(mClass, name, arg_types, 0);
}

public HackedConstructor constructor(final Class<?>... arg_types) throws HackDeclaration.HackAssertionException {
return new HackedConstructor(mClass, arg_types);
}

public Class<C> getmClass() {
return mClass;
}
}

如果你要获得静态方法，就调用staticMethod，静态变量就调用staticField，非静态方法就调用method，非静态变量就调用field，要获得构造函数就调用constructor，当然你也可以调用getmClass获得Class。最终如果你调用方法相关的函数会得到HackedMethod，调用变量相关的会得到HackedField，调用构造函数相关的会获得HackedConstructor，这三个类的源码如下。自己看源码。。。。不解释了。。。太长了，主要是对反射的封装，并达到面向对象的效果。

{

private final Field mField;

HackedField(final Class clazz, final String name, int modifiers) throws HackDeclaration.HackAssertionException {
Field field = null;
try {
if (clazz == null) {
return;
}
field = clazz.getDeclaredField(name);
if (modifiers > 0 && (field.getModifiers() & modifiers) != modifiers) {
fail(new HackDeclaration.HackAssertionException(field + " does not match modifiers: " + modifiers));
}
field.setAccessible(true);
} catch (final NoSuchFieldException e) {
HackDeclaration.HackAssertionException hae = new HackDeclaration.HackAssertionException(e);
hae.setHackedClass(clazz);
hae.setHackedFieldName(name);
fail(hae);
} finally {
mField = field;
}
}

@SuppressWarnings("unchecked")
public  HackedField ofGenericType(final Class type) throws HackDeclaration.HackAssertionException {
if (mField != null && !type.isAssignableFrom(mField.getType())) {
fail(new HackDeclaration.HackAssertionException(new ClassCastException(mField + " is not of type " + type)));
}
return (HackedField) this;
}

@SuppressWarnings("unchecked")
public HackedField ofType(final String type_name) throws HackDeclaration.HackAssertionException {
try {
return (HackedField) ofType(Class.forName(type_name));
} catch (final ClassNotFoundException e) {
fail(new HackDeclaration.HackAssertionException(e));
return this;
}
}

@SuppressWarnings("unchecked")
public  HackedField ofType(final Class type) throws HackDeclaration.HackAssertionException {
if (mField != null && !type.isAssignableFrom(mField.getType())) {
fail(new HackDeclaration.HackAssertionException(new ClassCastException(mField + " is not of type " + type)));
}
return (HackedField) this;
}

public void hijack(final C instance, final Interception.InterceptionHandler handler) {
final T delegatee = get(instance);
if (delegatee == null) {
throw new IllegalStateException("Cannot hijack null");
}
final Class[] interfaces = delegatee.getClass().getInterfaces();
set(instance, Interception.proxy(delegatee, handler, interfaces));
}

public T get(final C instance) {
try {
@SuppressWarnings("unchecked") final T value = (T) mField.get(instance);
return value;
} catch (final IllegalAccessException e) {
e.printStackTrace();
return null;
}
}

public void set(final C instance, final Object value) {
try {
mField.set(instance, value);
} catch (final IllegalAccessException e) {
e.printStackTrace();

}
}

public Field getField() {
return mField;
}
}

public static class HackedMethod {

protected final Method mMethod;

HackedMethod(final Class clazz, final String name, final Class[] arg_types, int modifiers) throws HackDeclaration.HackAssertionException {
Method method = null;
try {
if (clazz == null) {
return;
}
method = clazz.getDeclaredMethod(name, arg_types);
if (modifiers > 0 && (method.getModifiers() & modifiers) != modifiers) {
fail(new HackDeclaration.HackAssertionException(method + " does not match modifiers: " + modifiers));
}
method.setAccessible(true);
} catch (final NoSuchMethodException e) {
HackDeclaration.HackAssertionException hae = new HackDeclaration.HackAssertionException(e);
hae.setHackedClass(clazz);
hae.setHackedMethodName(name);
fail(hae);
} finally {
mMethod = method;
}
}

public Object invoke(final Object receiver, final Object... args) throws IllegalArgumentException, InvocationTargetException {
Object obj = null;
try {
obj = mMethod.invoke(receiver, args);
return obj;
} catch (final IllegalAccessException e) { /* Should never happen */
e.printStackTrace();
}
return obj;
}

public Method getMethod() {
return mMethod;
}
}

public static class HackedConstructor {

protected Constructor mConstructor;

HackedConstructor(final Class clazz, final Class[] arg_types) throws HackDeclaration.HackAssertionException {
try {
if (clazz == null) {
return;
}
mConstructor = clazz.getDeclaredConstructor(arg_types);
} catch (NoSuchMethodException e) {
HackDeclaration.HackAssertionException hae = new HackDeclaration.HackAssertionException(e);
hae.setHackedClass(clazz);
fail(hae);
}
}

public Object getInstance(final Object... arg_types) throws IllegalArgumentException {
Object obj = null;
mConstructor.setAccessible(true);
try {
obj = mConstructor.newInstance(arg_types);
} catch (Exception e) {
e.printStackTrace();
}
return obj;
}
}" data-snippet-id="ext.724d65d09729669340a38a5c5049e8cf" data-snippet-saved="false" data-codota-status="done">[code]
public static class HackedField<C, T> {

private final Field mField;

HackedField(final Class<C> clazz, final String name, int modifiers) throws HackDeclaration.HackAssertionException {
Field field = null;
try {
if (clazz == null) {
return;
}
field = clazz.getDeclaredField(name);
if (modifiers > 0 && (field.getModifiers() & modifiers) != modifiers) {
fail(new HackDeclaration.HackAssertionException(field + " does not match modifiers: " + modifiers));
}
field.setAccessible(true);
} catch (final NoSuchFieldException e) {
HackDeclaration.HackAssertionException hae = new HackDeclaration.HackAssertionException(e);
hae.setHackedClass(clazz);
hae.setHackedFieldName(name);
fail(hae);
} finally {
mField = field;
}
}

@SuppressWarnings("unchecked")
public <T2> HackedField<C, T2> ofGenericType(final Class<?> type) throws HackDeclaration.HackAssertionException {
if (mField != null && !type.isAssignableFrom(mField.getType())) {
fail(new HackDeclaration.HackAssertionException(new ClassCastException(mField + " is not of type " + type)));
}
return (HackedField<C, T2>) this;
}

@SuppressWarnings("unchecked")
public HackedField<C, T> ofType(final String type_name) throws HackDeclaration.HackAssertionException {
try {
return (HackedField<C, T>) ofType(Class.forName(type_name));
} catch (final ClassNotFoundException e) {
fail(new HackDeclaration.HackAssertionException(e));
return this;
}
}

@SuppressWarnings("unchecked")
public <T2> HackedField<C, T2> ofType(final Class<T2> type) throws HackDeclaration.HackAssertionException {
if (mField != null && !type.isAssignableFrom(mField.getType())) {
fail(new HackDeclaration.HackAssertionException(new ClassCastException(mField + " is not of type " + type)));
}
return (HackedField<C, T2>) this;
}

public void hijack(final C instance, final Interception.InterceptionHandler<?> handler) {
final T delegatee = get(instance);
if (delegatee == null) {
throw new IllegalStateException("Cannot hijack null");
}
final Class<?>[] interfaces = delegatee.getClass().getInterfaces();
set(instance, Interception.proxy(delegatee, handler, interfaces));
}

public T get(final C instance) {
try {
@SuppressWarnings("unchecked") final T value = (T) mField.get(instance);
return value;
} catch (final IllegalAccessException e) {
e.printStackTrace();
return null;
}
}

public void set(final C instance, final Object value) {
try {
mField.set(instance, value);
} catch (final IllegalAccessException e) {
e.printStackTrace();

}
}

public Field getField() {
return mField;
}
}

public static class HackedMethod {

protected final Method mMethod;

HackedMethod(final Class<?> clazz, final String name, final Class<?>[] arg_types, int modifiers) throws HackDeclaration.HackAssertionException {
Method method = null;
try {
if (clazz == null) {
return;
}
method = clazz.getDeclaredMethod(name, arg_types);
if (modifiers > 0 && (method.getModifiers() & modifiers) != modifiers) {
fail(new HackDeclaration.HackAssertionException(method + " does not match modifiers: " + modifiers));
}
method.setAccessible(true);
} catch (final NoSuchMethodException e) {
HackDeclaration.HackAssertionException hae = new HackDeclaration.HackAssertionException(e);
hae.setHackedClass(clazz);
hae.setHackedMethodName(name);
fail(hae);
} finally {
mMethod = method;
}
}

public Object invoke(final Object receiver, final Object... args) throws IllegalArgumentException, InvocationTargetException {
Object obj = null;
try {
obj = mMethod.invoke(receiver, args);
return obj;
} catch (final IllegalAccessException e) { /* Should never happen */
e.printStackTrace();
}
return obj;
}

public Method getMethod() {
return mMethod;
}
}

public static class HackedConstructor {

protected Constructor<?> mConstructor;

HackedConstructor(final Class<?> clazz, final Class<?>[] arg_types) throws HackDeclaration.HackAssertionException {
try {
if (clazz == null) {
return;
}
mConstructor = clazz.getDeclaredConstructor(arg_types);
} catch (NoSuchMethodException e) {
HackDeclaration.HackAssertionException hae = new HackDeclaration.HackAssertionException(e);
hae.setHackedClass(clazz);
fail(hae);
}
}

public Object getInstance(final Object... arg_types) throws IllegalArgumentException {
Object obj = null;
mConstructor.setAccessible(true);
try {
obj = mConstructor.newInstance(arg_types);
} catch (Exception e) {
e.printStackTrace();
}
return obj;
}
}

注意HackedField中有个方法叫hijack，这个方法的作用就是劫持。

最终，如果反射失败的话会进入Hack的fail方法处理，我们可以设置AssertionFailureHandler处理器，返回false会扔出异常，否则不会扔出异常。可以在里面做一些事，比如埋点。这样就可以集中到一个地方处理了。

private static void fail(HackDeclaration.HackAssertionException e) throws HackDeclaration.HackAssertionException {
if (sFailureHandler == null || !sFailureHandler.onAssertionFailure(e)) {
throw e;
}
}

public static void setAssertionFailureHandler(AssertionFailureHandler handler) {
sFailureHandler = handler;
}

public interface AssertionFailureHandler {
boolean onAssertionFailure(HackDeclaration.HackAssertionException failure);
}

瞎说了这么多，来实践一把。

获得HackedClass对象，调用Hack.into方法

hackPersonByClass = Hack.into(Student.class);
//输出class测试
System.out.println(hackPersonByClass.getmClass());
//通过Class的全类名获得一个HackedClass
Hack.HackedClass hackPersonByName = Hack.into("cn.edu.zafu.Student");
//输出class测试
System.out.println(hackPersonByName.getmClass());" data-snippet-id="ext.a40a5f5553d8573e25bdf902acd5e58f" data-snippet-saved="false" data-codota-status="done">[code]//通过Class来获得一个HackedClass
Hack.HackedClass<Student> hackPersonByClass = Hack.into(Student.class);
//输出class测试
System.out.println(hackPersonByClass.getmClass());
//通过Class的全类名获得一个HackedClass
Hack.HackedClass<Student> hackPersonByName = Hack.into("cn.edu.zafu.Student");
//输出class测试
System.out.println(hackPersonByName.getmClass());

创建实例，调用HackedClass的constructor方法，将参数的类型传入，然后调用getInstance方法就可以获得一个实例了。

//获得构造函数
Hack.HackedConstructor personConstructor = hackPersonByName.constructor(String.class, int.class);
//创建并获得实例
Student student = (Student) personConstructor.getInstance("区长", 121);
//输出结果测试
System.out.println(student);
//直接调用反射获得的对象的方法
student.say("世界你好,世界再见");

非静态变量需要通过field方法获得一个HackedField对象，这时候你获得的field是一个Object类型的，因此如果你想要类型安全，需要调用一下ofType方法，将类型传入。

ofType 获得一个HackedField,非静态
Hack.HackedField hackName = hackPersonByName.field("name").ofType(String.class);
//反射调用
String name = hackName.get(student);
//输出结果测试
System.out.println(name);

//通过field -> ofType 获得一个HackedField,非静态
Hack.HackedField hackAge = hackPersonByName.field("age").ofType(int.class);
//反射设置属性
hackAge.set(student, 16);
//反射获得age,进行验证
Integer age = hackPersonByName.field("age").ofType(int.class).get(student);
//输出结果测试
System.out.println(age);" data-snippet-id="ext.fa9eb43902e7e86f69da14bbbf3a323e" data-snippet-saved="false" data-codota-status="done">[code]//通过field -> ofType 获得一个HackedField,非静态
Hack.HackedField<Student, String> hackName = hackPersonByName.field("name").ofType(String.class);
//反射调用
String name = hackName.get(student);
//输出结果测试
System.out.println(name);

//通过field -> ofType 获得一个HackedField,非静态
Hack.HackedField<Student, Integer> hackAge = hackPersonByName.field("age").ofType(int.class);
//反射设置属性
hackAge.set(student, 16);
//反射获得age,进行验证
Integer age = hackPersonByName.field("age").ofType(int.class).get(student);
//输出结果测试
System.out.println(age);

静态变量直接调用staticField方法即可，除了上面的ofType将类型传入，这个类型可以是Class对象，也可以是Class字符串的全类名。

hackSchool = hackPersonByName.staticField("school").ofType("java.lang.String");

//获得静态变量值
String sSchool = (String) hackSchool.get(null);
//输出结果测试
System.out.println(sSchool);

//设置值
hackSchool.getField().set(null, "北京大学");
//获得值验证是否设置成功,通过getField()方式
sSchool = (String) hackSchool.getField().get(null);
//输出结果测试
System.out.println(sSchool);" data-snippet-id="ext.840950dfd42bf0f51202441c6563cc12" data-snippet-saved="false" data-codota-status="done">[code]
//反射获得静态变量
Hack.HackedField<Student, Object> hackSchool = hackPersonByName.staticField("school").ofType("java.lang.String");

//获得静态变量值
String sSchool = (String) hackSchool.get(null);
//输出结果测试
System.out.println(sSchool);

//设置值
hackSchool.getField().set(null, "北京大学");
//获得值验证是否设置成功,通过getField()方式
sSchool = (String) hackSchool.getField().get(null);
//输出结果测试
System.out.println(sSchool);

泛型参数可以调用ofGenericType方法转为泛型，比如下面的Map

> hackScores = hackPersonByName.field("scores").ofGenericType(Map.class);
Map stringIntegerMap = hackScores.get(student);
stringIntegerMap.put("语文", 80);
stringIntegerMap.put("数学", 90);
//泛型参数设置
hackScores.set(student, stringIntegerMap);
//输出结果测试
System.out.println(student.getScores());" data-snippet-id="ext.1ba30094a925872cd8b861cd077a907e" data-snippet-saved="false" data-codota-status="done">[code]//泛型参数
Hack.HackedField<Student, Map<String, Integer>> hackScores = hackPersonByName.field("scores").ofGenericType(Map.class);
Map<String, Integer> stringIntegerMap = hackScores.get(student);
stringIntegerMap.put("语文", 80);
stringIntegerMap.put("数学", 90);
//泛型参数设置
hackScores.set(student, stringIntegerMap);
//输出结果测试
System.out.println(student.getScores());

方法的调用需要调用method相关的方法，非静态方法直接调用method方法获得HackedMethod对象，需要将方法的参数类型传入。之后直接invoke调用的时候将调用对象实例和参数传入。

//反射非静态方法调用
hackPersonByName.method("say", String.class).invoke(student, "fuck the source code");

静态方法和非静态方法相比就是invoke的时候调用对象可以直接传null。

//反射静态方法调用
hackPersonByName.staticMethod("setSchool", String.class).invoke(null, "南京大学");
//输出结果测试
System.out.println(Student.getSchool());
//反射静态方法调用
String school = (String) hackPersonByName.staticMethod("getSchool").getMethod().invoke(null);
System.out.println(school);

以上调用的最终输出如下图所示,代码可能跟图有出入（貌似修改过前后顺序）



Hack类里的异常处理最终都会走到fail方法中，fail方法中会判断AssertionFailureHandler是否为空，空的情况下会直接扔出异常，否则会看AssertionFailureHandler的处理结果，如果结果返回true，则不扔出异常，返回fasle的情况下也会扔出异常，我们通过setAssertionFailureHandler方法设置一个异常处理器就可以了。下面调用两个不存在的字段，让它进入到这个处理器中，如果字段名是notHandler则扔出异常，否则输出信息并返回true。

hackedClass = failure.getHackedClass();
String hackedFieldName = failure.getHackedFieldName();
String hackedMethodName = failure.getHackedMethodName();
System.out.println("=====onAssertionFailure start=====");
System.out.println("hackedClass:" + hackedClass);
System.out.println("hackedFieldName:" + hackedFieldName);
System.out.println("hackedMethodName:" + hackedMethodName);
System.out.println("=====onAssertionFailure end=====");
//返回true不会抛出异常,否则抛出异常

return true;
}
});
//获得一个不存在的对象,验证onAssertionFailure回调
Hack.HackedField unknownField = hackPersonByName.field("unknownField").ofType(String.class);
Hack.HackedField notHandler = hackPersonByName.field("notHandler").ofType(String.class);
" data-snippet-id="ext.9ecd6bd84d1b21724eb64f71ae87101f" data-snippet-saved="false" data-codota-status="done">[code]//异常处理
Hack.setAssertionFailureHandler(new Hack.AssertionFailureHandler() {
@Override
public boolean onAssertionFailure(Hack.HackDeclaration.HackAssertionException failure) {
//如果是notHandler字段,则不处理,即扔出异常,否则打印输出,不扔出异常
if ("notHandler".equals(failure.getHackedFieldName())) {
return false;
}

Class<?> hackedClass = failure.getHackedClass();
String hackedFieldName = failure.getHackedFieldName();
String hackedMethodName = failure.getHackedMethodName();
System.out.println("=====onAssertionFailure start=====");
System.out.println("hackedClass:" + hackedClass);
System.out.println("hackedFieldName:" + hackedFieldName);
System.out.println("hackedMethodName:" + hackedMethodName);
System.out.println("=====onAssertionFailure end=====");
//返回true不会抛出异常,否则抛出异常

return true;
}
});
//获得一个不存在的对象,验证onAssertionFailure回调
Hack.HackedField<Student, String> unknownField = hackPersonByName.field("unknownField").ofType(String.class);
Hack.HackedField<Student, String> notHandler = hackPersonByName.field("notHandler").ofType(String.class);

最终的效果如下



劫持字段，字段的劫持就是通过动态代理来实现的，内部的逻辑如下

implements
InvocationHandler {
private T mDelegatee;

@Override
public Object invoke(Object obj, Method method, Object[] args)
throws Throwable {
Object obj2 = null;
try {
obj2 = method.invoke(delegatee(), args);
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e2) {
e2.printStackTrace();
} catch (InvocationTargetException e3) {
throw e3.getTargetException();
}
return obj2;
}

protected T delegatee() {
return this.mDelegatee;
}

void setDelegatee(T t) {
this.mDelegatee = t;
}
}" data-snippet-id="ext.908e22327e1ea819f85ed07937a157d7" data-snippet-saved="false" data-codota-status="done">[code]public static abstract class InterceptionHandler<T> implements
InvocationHandler {
private T mDelegatee;

@Override
public Object invoke(Object obj, Method method, Object[] args)
throws Throwable {
Object obj2 = null;
try {
obj2 = method.invoke(delegatee(), args);
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e2) {
e2.printStackTrace();
} catch (InvocationTargetException e3) {
throw e3.getTargetException();
}
return obj2;
}

protected T delegatee() {
return this.mDelegatee;
}

void setDelegatee(T t) {
this.mDelegatee = t;
}
}

这个字段的方法调用都是调用委托对象，这个对象就是我们原始的字段，这个delegatee方法我们可以重写返回新对象，这样就和反射直接替换没有什么差别了。当然也可以重写invoke方法，在调用前和调用后做一些处理。比如我做一些日志输出。如下代码

() {
@Override
public Object invoke(Object obj, Method method, Object[] args) throws Throwable {
System.out.println("hijack:[invoke start]");

Object o = super.invoke(obj, method, args);

System.out.println("hijack:[invoke end]");
return o;
}
};
//劫持behavior字段
hackPersonByName.field("behavior").hijack(student, handler);
//测试劫持效果
student.getBehavior().perform("sleep", "sleep 10h");" data-snippet-id="ext.3710ef91fd9836945d5edf969058baa6" data-snippet-saved="false" data-codota-status="done">[code]//字段劫持处理
Interception.InterceptionHandler handler = new Interception.InterceptionHandler<IBehavior>() {
@Override
public Object invoke(Object obj, Method method, Object[] args) throws Throwable {
System.out.println("hijack:[invoke start]");

Object o = super.invoke(obj, method, args);

System.out.println("hijack:[invoke end]");
return o;
}
};
//劫持behavior字段
hackPersonByName.field("behavior").hijack(student, handler);
//测试劫持效果
student.getBehavior().perform("sleep", "sleep 10h");

最终效果如下



好了说了这么多，还是不明白这个东西有什么软用呢？Android动态加载资源的时候我们需要用到的ContextImpl对象，需要对AssetManager和Resources需要做一些操作，就可以这么来了。

AssetManager;
public static HackedMethod AssetManager_addAssetPath;
public static HackedClass ContextImpl;
public static HackedField ContextImpl_mResources;
public static boolean sIsReflectChecked;
public static boolean sIsReflectAvailable;

public static boolean defineAndVerify() {
if (sIsReflectChecked) {
return sIsReflectAvailable;
}
Hacks hacks = new Hacks();
try {
Hack.setAssertionFailureHandler(hacks);
allClasses();
allConstructors();
allFields();
allMethods();
sIsReflectAvailable = true;
return sIsReflectAvailable;
} catch (Throwable e) {
e.printStackTrace();
} finally {
Hack.setAssertionFailureHandler(null);
sIsReflectChecked = true;
}
return false;
}

private static void allClasses() throws HackAssertionException {
AssetManager = Hack.into(AssetManager.class);
ContextImpl = Hack.into("android.app.ContextImpl");
}

private static void allConstructors() throws HackAssertionException {

}

private static void allFields() throws HackAssertionException {

ContextImpl_mResources = ContextImpl.field("mResources").ofType(
Resources.class);
}

private static void allMethods() throws HackAssertionException {
AssetManager_addAssetPath = AssetManager.method("addAssetPath", String.class);
}

@Override
public boolean onAssertionFailure(HackAssertionException hackAssertionException) {
//throw it
return false;
}
}" data-snippet-id="ext.761aabe2bd8c30242e974baa0a5b4f3f" data-snippet-saved="false" data-codota-status="done">[code]

import java.lang.reflect.InvocationTargetException;

public class Hacks extends HackDeclaration implements
AssertionFailureHandler {

public static HackedClass<AssetManager> AssetManager;
public static HackedMethod AssetManager_addAssetPath;
public static HackedClass<Object> ContextImpl;
public static HackedField<Object, Resources> ContextImpl_mResources;
public static boolean sIsReflectChecked;
public static boolean sIsReflectAvailable;

public static boolean defineAndVerify() {
if (sIsReflectChecked) {
return sIsReflectAvailable;
}
Hacks hacks = new Hacks();
try {
Hack.setAssertionFailureHandler(hacks);
allClasses();
allConstructors();
allFields();
allMethods();
sIsReflectAvailable = true;
return sIsReflectAvailable;
} catch (Throwable e) {
e.printStackTrace();
} finally {
Hack.setAssertionFailureHandler(null);
sIsReflectChecked = true;
}
return false;
}

private static void allClasses() throws HackAssertionException {
AssetManager = Hack.into(AssetManager.class);
ContextImpl = Hack.into("android.app.ContextImpl");
}

private static void allConstructors() throws HackAssertionException {

}

private static void allFields() throws HackAssertionException {

ContextImpl_mResources = ContextImpl.field("mResources").ofType(
Resources.class);
}

private static void allMethods() throws HackAssertionException {
AssetManager_addAssetPath = AssetManager.method("addAssetPath", String.class);
}

@Override
public boolean onAssertionFailure(HackAssertionException hackAssertionException) {
//throw it
return false;
}
}

调用 Hacks.defineAndVerify反复进行定义和验证，成功后就可以直接调用了。

boolean flag = Hacks.defineAndVerify();

if (flag) {
AssetManager assetManager = AssetManager.class.newInstance();
Hacks.AssetManager_addAssetPath.invoke(assetManager,"assetPath");
Hacks.ContextImpl_mResources.set(context, resources);
}

上面的这个例子是伪代码，实际情况自己去把握~~~~写的比较随意，看看就好了~