Mybatis源码解读（二）--反射模块
Mybatis反射模块的代码在org.apache.ibatis.reflection。Mybatis的反射十分强大，对jdk的反射进行了很好的封装，完全可以作为一个独立的工具类在其他项目中使用。
核心类解读
MetaObject：封装了对象的元信息，包装了Mybatis中五个核心的反射类。也是提供给外部使用的反射工具类，通过它可以读取或修改对象的属性。
public class MetaObject {
//原始的java对象
private final Object originalObject;
private final ObjectWrapper objectWrapper;
private final ObjectFactory objectFactory;
private final ObjectWrapperFactory objectWrapperFactory;
private final ReflectorFactory reflectorFactory;ObjectFactory：对象工厂。Mybatis每次创建结果对象的新实例时，它都会使用ObjectFactory去创建POJO。
public interface ObjectFactory {
//设置配置信息
void setProperties(Properties properties);
//通过无参构造函数创建指定类的对象
T create(Class type);
//根据参数列表，选择合适的构造函数创建对象
T create(Class type, List> constructorArgTypes, List
ReflectorFactory：创建Reflector的工厂类，Reflector是Mybatis反射模块的基础，每个Reflector对象都对应一个类，在其中缓存了反射操作所需要的类的信息。
public interface ReflectorFactory {
boolean isClassCacheEnabled();
void setClassCacheEnabled(boolean classCacheEnabled);
Reflector findForClass(Class type);
}
ObjectWrapper：对象的包装，抽象了对象的属性信息，定义了一系列查询对象属性信息的方法，以及更新属性的方法。
public interface ObjectWrapper {
//获取对象指定属性的值
Object get(PropertyTokenizer prop);
//设置对象指定属性的值
void set(PropertyTokenizer prop, Object value);
String findProperty(String name, boolean useCamelCaseMapping);
String[] getGetterNames();
String[] getSetterNames();
Class getSetterType(String name);
Class getGetterType(String name);
boolean hasSetter(String name);
boolean hasGetter(String name);
MetaObject instantiatePropertyValue(String name, PropertyTokenizer prop, ObjectFactory objectFactory);
//判断当前对象是否为集合
boolean isCollection();
//当前集合添加一个元素
void add(Object element);
//当前集合添加另外一个集合
void addAll(List element);
}
ObjectWrapperFactory：ObjectWrapper的工厂类，用于创建ObjectWrapper。
public interface ObjectWrapperFactory {
boolean hasWrapperFor(Object object);
ObjectWrapper getWrapperFor(MetaObject metaObject, Object object);
}如何使用Mybatis反射模块
模拟一个实体类TUSer
@Data
public class TUser implements Serializable {
private Integer id;
private String userName;
}使用Reflector读取类元信息ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
Reflector findForClass = reflectorFactory.findForClass(TUser.class);
Constructor defaultConstructor = findForClass.getDefaultConstructor();
String[] getablePropertyNames = findForClass.getGetablePropertyNames();
String[] setablePropertyNames = findForClass.getSetablePropertyNames();
System.out.println(defaultConstructor.getName());
System.out.println(Arrays.toString(getablePropertyNames));
System.out.println(Arrays.toString(setablePropertyNames));
使用ObjectWrapper读取对象信息，并对对象属性进行赋值操作ObjectFactory objectFactory = new DefaultObjectFactory();
TUser user = objectFactory.create(TUser.class);
ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
MetaObject metaObject = MetaObject.forObject(user, objectFactory, objectWrapperFactory, reflectorFactory);
TUser userTemp = new TUser();
ObjectWrapper wrapperForUser = new BeanWrapper(metaObject, userTemp);
String[] getterNames = wrapperForUser.getGetterNames();
String[] setterNames = wrapperForUser.getSetterNames();
System.out.println(Arrays.toString(getterNames));
System.out.println(Arrays.toString(setterNames));
PropertyTokenizer prop = new PropertyTokenizer("userName");
wrapperForUser.set(prop, "test001");
System.out.println(userTemp);模拟数据库行数据转化成对象//1.模拟从数据库读取数据
Map dbResult = new HashMap<>();
dbResult.put("id", 1);
dbResult.put("user_name", "test001");
//2.模拟ResultMap映射关系
Map mapper = new HashMap();
mapper.put("id", "id");
mapper.put("userName", "user_name");
//3.使用反射工具类将行数据转换成pojo
BeanWrapper objectWrapper = (BeanWrapper) metaObject.getObjectWrapper();
Set> entrySet = mapper.entrySet();
for (Entry colInfo : entrySet) {
String propName = colInfo.getKey();
Object propValue = dbResult.get(colInfo.getValue());
PropertyTokenizer proTokenizer = new PropertyTokenizer(propName);
objectWrapper.set(proTokenizer, propValue);
}
System.out.println(metaObject.getOriginalObject());