Mybatis框架基础支持层——反射工具箱之Reflector&ReflectorFactory（3）
2024-09-03 13:34:32
说明：Reflector是Mybatis反射工具的基础，每个Reflector对应一个类，在Reflector中封装有该类的元信息，
以及基于类信息的一系列反射应用封装API
public class Reflector {
private static final String[] EMPTY_STRING_ARRAY = new String[0];
/**
* 对应的类Class对象
*/
private Class<?> type;
/**
* 类中可读属性的集合，就是存在相应的getter方法的属性
*/
private String[] readablePropertyNames = EMPTY_STRING_ARRAY;
/**
* 类中可写属性的集合，就是存在相应的setter方法的属性
*/
private String[] writeablePropertyNames = EMPTY_STRING_ARRAY;
/**
* 记录了属性相应的setter方法，key是属性名称，value是invoker对象，
* invoker是对setter方法对应Method对象的封装
*/
private Map<String, Invoker> setMethods = new HashMap<String, Invoker>();
/**
* 记录了属性相应的getter方法，key是属性名称，value是invoker对象，
* invoker是对getter方法对应Method对象的封装
*/
private Map<String, Invoker> getMethods = new HashMap<String, Invoker>();
/**
* 记录了属性相应的setter方法的参数值类型，key是属性名称，value是setter方法的参数值类型
*/
private Map<String, Class<?>> setTypes = new HashMap<String, Class<?>>();
/**
* 记录了属性相应的getter方法的返回值类型，key是属性名称，value是getter方法的返回值类型
*/
private Map<String, Class<?>> getTypes = new HashMap<String, Class<?>>();
/**
* 记录了默认构造方法
*/
private Constructor<?> defaultConstructor;
/**
* 记录了所有属性名称的集合
*/
private Map<String, String> caseInsensitivePropertyMap = new HashMap<String, String>();
/**
* 在Reflector构造方法中会指定某个类的Class对象，并填充上述集合
*/
public Reflector(Class<?> clazz) {
type = clazz;
/**
* 查找clazz的默认构造方法（无参构造）
*/
addDefaultConstructor(clazz);
/**
* 处理clazz中的getter方法，填充getMethods集合和getTypes集合
*/
addGetMethods(clazz);
/**
* 处理clazz中的setter方法，填充setMethods集合和setTypes集合
*/
addSetMethods(clazz);
/**
* 处理没有getter/setter方法的字段
*/
addFields(clazz);
/**
* 根据getMethods、setMethods集合，初始化可读/写属性名称的集合
*/
readablePropertyNames = getMethods.keySet().toArray(new String[getMethods.keySet().size()]);
writeablePropertyNames = setMethods.keySet().toArray(new String[setMethods.keySet().size()]);
/**
* 初始化caseInsensitivePropertyMap，其中记录了所有大写格式的属性名称
*/
for (String propName : readablePropertyNames) {
caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
}
for (String propName : writeablePropertyNames) {
caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
}
}
private void addDefaultConstructor(Class<?> clazz) {
/**
* 返回类中声明的所有构造函数Constructor，包括public、protected、default、private声明
* 如果Class对象是一个接口、抽象类、数组类或void，则返回length=0的Constructor数组
*/
Constructor<?>[] consts = clazz.getDeclaredConstructors();
for (Constructor<?> constructor : consts) {
if (constructor.getParameterTypes().length == 0) {
if (canAccessPrivateMethods()) {
try {
constructor.setAccessible(true);
} catch (Exception e) {
// Ignored. This is only a final precaution, nothing we can do.
}
}
if (constructor.isAccessible()) {
this.defaultConstructor = constructor;
}
}
}
}
private void addGetMethods(Class<?> cls) {
Map<String, List<Method>> conflictingGetters = new HashMap<String, List<Method>>();
/**
* 获取当前类中所有的方法，包括自己、父类、父类的父类...,接口等
*/
Method[] methods = getClassMethods(cls);
for (Method method : methods) {
String name = method.getName();
if (name.startsWith("get") && name.length() > 3) {
if (method.getParameterTypes().length == 0) {
/**
* PropertyNamer：
* setter、getter方法名=>属性名称转换,和属性getter、setter方法判断
*/
name = PropertyNamer.methodToProperty(name);
addMethodConflict(conflictingGetters, name, method);
}
} else if (name.startsWith("is") && name.length() > 2) {
if (method.getParameterTypes().length == 0) {
name = PropertyNamer.methodToProperty(name);
addMethodConflict(conflictingGetters, name, method);
}
}
}
//填充getMethods和getTypes集合
resolveGetterConflicts(conflictingGetters);
}
private void resolveGetterConflicts(Map<String, List<Method>> conflictingGetters) {
for (String propName : conflictingGetters.keySet()) {
List<Method> getters = conflictingGetters.get(propName);
Iterator<Method> iterator = getters.iterator();
Method firstMethod = iterator.next();
if (getters.size() == 1) {
addGetMethod(propName, firstMethod);
} else {
Method getter = firstMethod;
Class<?> getterType = firstMethod.getReturnType();
while (iterator.hasNext()) {
Method method = iterator.next();
Class<?> methodType = method.getReturnType();
if (methodType.equals(getterType)) {
throw new ReflectionException("Illegal overloaded getter method with ambiguous type for property "
+ propName + " in class " + firstMethod.getDeclaringClass()
+ ". This breaks the JavaBeans " + "specification and can cause unpredictable results.");
} else if (methodType.isAssignableFrom(getterType)) {
// OK getter type is descendant
} else if (getterType.isAssignableFrom(methodType)) {
getter = method;
getterType = methodType;
} else {
throw new ReflectionException("Illegal overloaded getter method with ambiguous type for property "
+ propName + " in class " + firstMethod.getDeclaringClass()
+ ". This breaks the JavaBeans " + "specification and can cause unpredictable results.");
}
}
addGetMethod(propName, getter);
}
}
}
private void addGetMethod(String name, Method method) {
if (isValidPropertyName(name)) {
getMethods.put(name, new MethodInvoker(method));
Type returnType = TypeParameterResolver.resolveReturnType(method, type);
getTypes.put(name, typeToClass(returnType));
}
}
private void addSetMethods(Class<?> cls) {
Map<String, List<Method>> conflictingSetters = new HashMap<String, List<Method>>();
Method[] methods = getClassMethods(cls);
for (Method method : methods) {
String name = method.getName();
if (name.startsWith("set") && name.length() > 3) {
if (method.getParameterTypes().length == 1) {
name = PropertyNamer.methodToProperty(name);
addMethodConflict(conflictingSetters, name, method);
}
}
}
resolveSetterConflicts(conflictingSetters);
}
private void addMethodConflict(Map<String, List<Method>> conflictingMethods, String name, Method method) {
List<Method> list = conflictingMethods.get(name);
if (list == null) {
list = new ArrayList<Method>();
conflictingMethods.put(name, list);
}
list.add(method);
}
private void resolveSetterConflicts(Map<String, List<Method>> conflictingSetters) {
for (String propName : conflictingSetters.keySet()) {
List<Method> setters = conflictingSetters.get(propName);
Class<?> getterType = getTypes.get(propName);
Method match = null;
ReflectionException exception = null;
for (Method setter : setters) {
Class<?> paramType = setter.getParameterTypes()[0];
if (paramType.equals(getterType)) {
// should be the best match
match = setter;
break;
}
if (exception == null) {
try {
match = pickBetterSetter(match, setter, propName);
} catch (ReflectionException e) {
// there could still be the 'best match'
match = null;
exception = e;
}
}
}
if (match == null) {
throw exception;
} else {
addSetMethod(propName, match);
}
}
}
private Method pickBetterSetter(Method setter1, Method setter2, String property) {
if (setter1 == null) {
return setter2;
}
Class<?> paramType1 = setter1.getParameterTypes()[0];
Class<?> paramType2 = setter2.getParameterTypes()[0];
if (paramType1.isAssignableFrom(paramType2)) {
return setter2;
} else if (paramType2.isAssignableFrom(paramType1)) {
return setter1;
}
throw new ReflectionException("Ambiguous setters defined for property '" + property + "' in class '"
+ setter2.getDeclaringClass() + "' with types '" + paramType1.getName() + "' and '"
+ paramType2.getName() + "'.");
}
private void addSetMethod(String name, Method method) {
if (isValidPropertyName(name)) {
setMethods.put(name, new MethodInvoker(method));
// TypeParameterResolver解析类型，下一篇博文介绍
Type[] paramTypes = TypeParameterResolver.resolveParamTypes(method, type);
setTypes.put(name, typeToClass(paramTypes[0]));
}
}
private Class<?> typeToClass(Type src) {
Class<?> result = null;
if (src instanceof Class) {
result = (Class<?>) src;
} else if (src instanceof ParameterizedType) {
result = (Class<?>) ((ParameterizedType) src).getRawType();
} else if (src instanceof GenericArrayType) {
Type componentType = ((GenericArrayType) src).getGenericComponentType();
if (componentType instanceof Class) {
result = Array.newInstance((Class<?>) componentType, 0).getClass();
} else {
Class<?> componentClass = typeToClass(componentType);
result = Array.newInstance((Class<?>) componentClass, 0).getClass();
}
}
if (result == null) {
result = Object.class;
}
return result;
}
private void addFields(Class<?> clazz) {
Field[] fields = clazz.getDeclaredFields();
for (Field field : fields) {
if (canAccessPrivateMethods()) {
try {
field.setAccessible(true);
} catch (Exception e) {
// Ignored. This is only a final precaution, nothing we can do.
}
}
if (field.isAccessible()) {
if (!setMethods.containsKey(field.getName())) {
// issue #379 - removed the check for final because JDK 1.5 allows
// modification of final fields through reflection (JSR-133). (JGB)
// pr #16 - final static can only be set by the classloader
int modifiers = field.getModifiers();
if (!(Modifier.isFinal(modifiers) && Modifier.isStatic(modifiers))) {
addSetField(field);
}
}
if (!getMethods.containsKey(field.getName())) {
addGetField(field);
}
}
}
//递归
if (clazz.getSuperclass() != null) {
addFields(clazz.getSuperclass());
}
}
private void addSetField(Field field) {
if (isValidPropertyName(field.getName())) {
setMethods.put(field.getName(), new SetFieldInvoker(field));
Type fieldType = TypeParameterResolver.resolveFieldType(field, type);
setTypes.put(field.getName(), typeToClass(fieldType));
}
}
private void addGetField(Field field) {
if (isValidPropertyName(field.getName())) {
getMethods.put(field.getName(), new GetFieldInvoker(field));
Type fieldType = TypeParameterResolver.resolveFieldType(field, type);
getTypes.put(field.getName(), typeToClass(fieldType));
}
}
private boolean isValidPropertyName(String name) {
return !(name.startsWith("$") || "serialVersionUID".equals(name) || "class".equals(name));
}
/*
* This method returns an array containing all methods
* declared in this class and any superclass.
* We use this method, instead of the simpler Class.getMethods(),
* because we want to look for private methods as well.
*
* @param cls The class
* @return An array containing all methods in this class
*/
private Method[] getClassMethods(Class<?> cls) {
//key是方法签名（唯一标识，下文生成），value是Method对象
Map<String, Method> uniqueMethods = new HashMap<String, Method>();
Class<?> currentClass = cls;
while (currentClass != null) {
/**
* currentClass.getDeclaredMethods()返回当前类或接口中所有被声明的方法，包括
* public、protected、default、private，但是排除集成的方法
*
* 此方法是将当前类中非桥接（下文有介绍）方法填入uniqueMethods集合
*/
addUniqueMethods(uniqueMethods, currentClass.getDeclaredMethods());
// we also need to look for interface methods -
// because the class may be abstract
Class<?>[] interfaces = currentClass.getInterfaces();
for (Class<?> anInterface : interfaces) {
addUniqueMethods(uniqueMethods, anInterface.getMethods());
}
/**
* Returns the {@code Class} representing the superclass of the entity
* (class, interface, primitive type or void) represented by this
* {@code Class}. If this {@code Class} represents either the
* {@code Object} class, an interface, a primitive type, or void, then
* null is returned. If this object represents an array class then the
* {@code Class} object representing the {@code Object} class is
* returned
*/
currentClass = currentClass.getSuperclass();
}
Collection<Method> methods = uniqueMethods.values();
return methods.toArray(new Method[methods.size()]);
}
private void addUniqueMethods(Map<String, Method> uniqueMethods, Method[] methods) {
for (Method currentMethod : methods) {
/**
* 桥接方法是 JDK 1.5 引入泛型后，为了使Java的泛型方法生成的字节码和 1.5 版本前的字节码相兼容，
* 由编译器自动生成的方法。我们可以通过Method.isBridge()方法来判断一个方法是否是桥接方法。
*/
if (!currentMethod.isBridge()) {
//获取当前方法的签名
String signature = getSignature(currentMethod);
// check to see if the method is already known
// if it is known, then an extended class must have
// overridden a method
if (!uniqueMethods.containsKey(signature)) {
if (canAccessPrivateMethods()) {
try {
currentMethod.setAccessible(true);
} catch (Exception e) {
// Ignored. This is only a final precaution, nothing we can do.
}
}
uniqueMethods.put(signature, currentMethod);
}
}
}
}
/**
* 获取一个方法的签名，根据方法的返回值、方法、方法参数构建一个签名
*/
private String getSignature(Method method) {
StringBuilder sb = new StringBuilder();
Class<?> returnType = method.getReturnType();
if (returnType != null) {
sb.append(returnType.getName()).append('#');
}
sb.append(method.getName());
Class<?>[] parameters = method.getParameterTypes();
for (int i = 0; i < parameters.length; i++) {
if (i == 0) {
sb.append(':');
} else {
sb.append(',');
}
sb.append(parameters[i].getName());
}
return sb.toString();
}
private static boolean canAccessPrivateMethods() {
try {
//java安全管理器具体细节，可看博客中另一篇介绍
SecurityManager securityManager = System.getSecurityManager();
if (null != securityManager) {
securityManager.checkPermission(new ReflectPermission("suppressAccessChecks"));
}
} catch (SecurityException e) {
return false;
}
return true;
}
/*
* Gets the name of the class the instance provides information for
*
* @return The class name
*/
public Class<?> getType() {
return type;
}
public Constructor<?> getDefaultConstructor() {
if (defaultConstructor != null) {
return defaultConstructor;
} else {
throw new ReflectionException("There is no default constructor for " + type);
}
}
public boolean hasDefaultConstructor() {
return defaultConstructor != null;
}
public Invoker getSetInvoker(String propertyName) {
Invoker method = setMethods.get(propertyName);
if (method == null) {
throw new ReflectionException("There is no setter for property named '" + propertyName + "' in '" + type + "'");
}
return method;
}
public Invoker getGetInvoker(String propertyName) {
Invoker method = getMethods.get(propertyName);
if (method == null) {
throw new ReflectionException("There is no getter for property named '" + propertyName + "' in '" + type + "'");
}
return method;
}
/*
* Gets the type for a property setter
*
* @param propertyName - the name of the property
* @return The Class of the propery setter
*/
public Class<?> getSetterType(String propertyName) {
Class<?> clazz = setTypes.get(propertyName);
if (clazz == null) {
throw new ReflectionException("There is no setter for property named '" + propertyName + "' in '" + type + "'");
}
return clazz;
}
/*
* Gets the type for a property getter
*
* @param propertyName - the name of the property
* @return The Class of the propery getter
*/
public Class<?> getGetterType(String propertyName) {
Class<?> clazz = getTypes.get(propertyName);
if (clazz == null) {
throw new ReflectionException("There is no getter for property named '" + propertyName + "' in '" + type + "'");
}
return clazz;
}
/*
* Gets an array of the readable properties for an object
*
* @return The array
*/
public String[] getGetablePropertyNames() {
return readablePropertyNames;
}
/*
* Gets an array of the writeable properties for an object
*
* @return The array
*/
public String[] getSetablePropertyNames() {
return writeablePropertyNames;
}
/*
* Check to see if a class has a writeable property by name
*
* @param propertyName - the name of the property to check
* @return True if the object has a writeable property by the name
*/
public boolean hasSetter(String propertyName) {
return setMethods.keySet().contains(propertyName);
}
/*
* Check to see if a class has a readable property by name
*
* @param propertyName - the name of the property to check
* @return True if the object has a readable property by the name
*/
public boolean hasGetter(String propertyName) {
return getMethods.keySet().contains(propertyName);
}
public String findPropertyName(String name) {
return caseInsensitivePropertyMap.get(name.toUpperCase(Locale.ENGLISH));
}
}
ReflectorFactory接口主要实现了对Reflector对象的创建和缓存，Mybatis为该接口提供了仅有的一个实现类DefaultReflectorFactory：
public interface ReflectorFactory {
/**
* 检测ReflectorFactory对象是否启用缓存Reflector功能
*/
boolean isClassCacheEnabled();
/**
* 设置ReflectorFactory对象是否启用缓存Reflector功能
*/
void setClassCacheEnabled(boolean classCacheEnabled);
/**
* 创建指定Class对象对应的Reflector，如果缓存有，就从缓存取，否则新建一个
*/
Reflector findForClass(Class<?> type);
}
public class DefaultReflectorFactory implements ReflectorFactory {
/**
* 默认启用缓存Reflector的功能
*/
private boolean classCacheEnabled = true;
/**
* 缓存Reflector的数据结构，key[Class对象]，value[Class对应的Reflector对象]
*/
private final ConcurrentMap<Class<?>, Reflector> reflectorMap = new ConcurrentHashMap<Class<?>, Reflector>();
public DefaultReflectorFactory() {
}
@Override
public boolean isClassCacheEnabled() {
return classCacheEnabled;
}
@Override
public void setClassCacheEnabled(boolean classCacheEnabled) {
this.classCacheEnabled = classCacheEnabled;
}
@Override
public Reflector findForClass(Class<?> type) {
if (classCacheEnabled) {
// synchronized (type) removed see issue #461
Reflector cached = reflectorMap.get(type);
if (cached == null) {
cached = new Reflector(type);
reflectorMap.put(type, cached);
}
return cached;
} else {
return new Reflector(type);
}
}
}
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