注释mybatis-Reflector
2019-07-05 本文已影响0人
lazyguy
/**
* Copyright 2009-2019 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package org.apache.ibatis.reflection;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.ReflectPermission;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Map.Entry;
import org.apache.ibatis.reflection.invoker.GetFieldInvoker;
import org.apache.ibatis.reflection.invoker.Invoker;
import org.apache.ibatis.reflection.invoker.MethodInvoker;
import org.apache.ibatis.reflection.invoker.SetFieldInvoker;
import org.apache.ibatis.reflection.property.PropertyNamer;
/**
* This class represents a cached set of class definition information that allows for easy mapping
* between property names and getter/setter methods. 这个类抽取一个Class的各种相关元信息缓存起来。
* 主要是一个JAVABEAN的property名字和对应的getter/setter方法。
*
* @author Clinton Begin
*/
public class Reflector {
//传入的的Class对象，实际应用的时候就是我们定义的javabean
private final Class<?> type;
//可读property的名字数组，只有有对应的getter方法的property才是可读的
private final String[] readablePropertyNames;
//同理
private final String[] writablePropertyNames;
//
private final Map<String, Invoker> setMethods = new HashMap<>();
private final Map<String, Invoker> getMethods = new HashMap<>();
private final Map<String, Class<?>> setTypes = new HashMap<>();
private final Map<String, Class<?>> getTypes = new HashMap<>();
private Constructor<?> defaultConstructor;
private Map<String, String> caseInsensitivePropertyMap = new HashMap<>();
/**
* 这个类的主要逻辑就是就是抽取Class的元信息，就在构造函数中完成的。
*/
public Reflector(Class<?> clazz) {
type = clazz;
addDefaultConstructor(clazz);
addGetMethods(clazz);
addSetMethods(clazz);
addFields(clazz);
readablePropertyNames = getMethods.keySet().toArray(new String[getMethods.keySet().size()]);
writablePropertyNames = setMethods.keySet().toArray(new String[setMethods.keySet().size()]);
//将解析出来的属性再做一次大写转换作为key存起来
for (String propName : readablePropertyNames) {
caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
}
for (String propName : writablePropertyNames) {
caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
}
//所以整个解析过程就是在解析getter/setter方法和field字段成为property。封装到对应Invoker中存起来
//Invoker其实就是封装对应的方法/Field的简便容器
}
/**
* Checks whether can control member accessible.
*
* @return If can control member accessible, it return {@literal true}
* @since 3.5.0
*/
public static boolean canControlMemberAccessible() {
try {
SecurityManager securityManager = System.getSecurityManager();
if (null != securityManager) {
securityManager.checkPermission(new ReflectPermission("suppressAccessChecks"));
}
} catch (SecurityException e) {
return false;
}
return true;
}
/**
* 抽取class的默认构造函数，就是没有任何参数那一个
*/
private void addDefaultConstructor(Class<?> clazz) {
/**
* 抽取出JAVABEAN里面那个没有参数的那个构造器.注意Class类里面有很多getDeclaredXXX的方法。
* 这个Declared的意思是声明的。所谓getDeclaredXXX，既获取由这个Class本身声明的各种对应的XXX（构造器，方法，属性，注解）
* public，private，protected的都包括。
* 但是不会包括从父类继承而来的，因为父类和接口的来的不是它自己“Declared”的。
*/
Constructor<?>[] consts = clazz.getDeclaredConstructors();
for (Constructor<?> constructor : consts) {
if (constructor.getParameterTypes().length == 0) {
this.defaultConstructor = constructor;
}
}
}
/**
* 抽取property的Getter方法
*/
private void addGetMethods(Class<?> cls) {
Map<String, List<Method>> conflictingGetters = new HashMap<>();
Method[] methods = getClassMethods(cls);
//有参数的不符合getter方法规范，过滤掉
for (Method method : methods) {
if (method.getParameterTypes().length > 0) {
continue;
}
String name = method.getName();
//必须以get/is开头
if ((name.startsWith("get") && name.length() > 3)
|| (name.startsWith("is") && name.length() > 2)) {
//javaBean的property叫啥是由方法名决定的。所以专门写了一个工具解析对应的property
name = PropertyNamer.methodToProperty(name);
addMethodConflict(conflictingGetters, name, method);
}
}
resolveGetterConflicts(conflictingGetters);
}
/**
* 这里又一次再处理重复方法，其实任然是子类重写父类方法引起的问题。 我们在addUniqueMethods中已经过滤了一遍重载方法，为什么这里又有呢？
* 原因是重载不仅仅是可能一模一样，也有可能返回值不同。比如父类返回List，子类返回ArrayList。 而在我们解析Signature里面返回值是算在了里面的。所以就可能出现2个方法，除了返回值不一样，其他都一样
* 此时我们取返回值范围为较小的那个。既ArrayList
*/
private void resolveGetterConflicts(Map<String, List<Method>> conflictingGetters) {
for (Entry<String, List<Method>> entry : conflictingGetters.entrySet()) {
Method winner = null;
String propName = entry.getKey();
for (Method candidate : entry.getValue()) {
if (winner == null) {
winner = candidate;
continue;
}
Class<?> winnerType = winner.getReturnType();
Class<?> candidateType = candidate.getReturnType();
if (candidateType.equals(winnerType)) {
if (!boolean.class.equals(candidateType)) {
throw new ReflectionException(
"Illegal overloaded getter method with ambiguous type for property "
+ propName + " in class " + winner.getDeclaringClass()
+ ". This breaks the JavaBeans specification and can cause unpredictable results.");
} else if (candidate.getName().startsWith("is")) {
winner = candidate;
}
} else if (candidateType.isAssignableFrom(winnerType)) {
// OK getter type is descendant
} else if (winnerType.isAssignableFrom(candidateType)) {
winner = candidate;
} else {
throw new ReflectionException(
"Illegal overloaded getter method with ambiguous type for property "
+ propName + " in class " + winner.getDeclaringClass()
+ ". This breaks the JavaBeans specification and can cause unpredictable results.");
}
}
addGetMethod(propName, winner);
}
}
/**
* 将proerty和对应的getter放入容器
* @param name
* @param method
*/
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<>();
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.computeIfAbsent(name, k -> new ArrayList<>());
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));
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(componentClass, 0).getClass();
}
}
if (result == null) {
result = Object.class;
}
return result;
}
/**
* 抽取Class本身的成员变量field，注意它不是javaBean中的property
* @param clazz
*/
private void addFields(Class<?> clazz) {
Field[] fields = clazz.getDeclaredFields();
for (Field field : fields) {
//如果之前通过解析getter/setter得到的property没有包含当前field，
//也会解析出来放入对应的setMethods，getMethods，getTypes
//而且同理，父类的field依样画葫芦
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);
}
}
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 <code>Class.getMethods()</code>, because we want to
* look for private methods as well.
*
* 这是一个反射API很常见的使用场景，获取一个类的“所有方法”。 因为getDeclaredMethods和getMethods， 前者不能获取父类接口的方法，后者不能获取私有方法。
* 所以就用getDeclaredMethods和循环往上查找来获取所有方法。
*
* @param cls The class
* @return An array containing all methods in this class
*/
private Method[] getClassMethods(Class<?> cls) {
Map<String, Method> uniqueMethods = new HashMap<>();
Class<?> currentClass = cls;
while (currentClass != null && currentClass != Object.class) {
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());
}
currentClass = currentClass.getSuperclass();
}
Collection<Method> methods = uniqueMethods.values();
return methods.toArray(new Method[methods.size()]);
}
/**
* 这个方法会先剔除掉桥接方法，同时剔除掉重复的方法。 为什么一个类里面会有重复方法？ 当子类重写了父类的一个方法时，父类和子类的Class.getDeclaredMethods都能取到同名的一个方法,虽然声明的类不同
* 但我们的getSignature不考虑class的名字作为key，显然我们只想要子类的，所以后面加入的就不用放入map了
*/
private void addUniqueMethods(Map<String, Method> uniqueMethods, Method[] methods) {
for (Method currentMethod : methods) {
if (!currentMethod.isBridge()) {
//key的拼接规则
//Reflector.getSignature(Method)方法的唯一签名是：
//java.lang.String#getSignature:java.lang.reflect.Method
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)) {
uniqueMethods.put(signature, currentMethod);
}
}
}
}
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();
}
/**
* 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 property 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 property 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 writable properties for an object.
*
* @return The array
*/
public String[] getSetablePropertyNames() {
return writablePropertyNames;
}
/**
* Check to see if a class has a writable property by name.
*
* @param propertyName - the name of the property to check
* @return True if the object has a writable 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));
}
}
