Mybatis基础组件反射模块第六章

学习该组件可以让你深入理解JDK反射机制。

从解析配置文件获取到class对象然后在创建对象再对该对象进行赋值操作主要经过一下几个步骤

• 获取到class的全类路径
• 创建该类的对象
• 对该对象进行赋值操作

JavaBean规范

JavaBean具有如下特征
1、所有的属性都是私有的（通过 getter和setter 访问）
2、拥有公有的无参数构造函数
3、提供 setter/getter
4、实现 Serializable 接口

mybaits源码包结构

主要路径下面的包源码分析 Reflector和ReflectorFactory

Reflector类主要保存的是类的元数据信息

• 类的类型
• 类的get/setf方法
• get/set类的参数
• 默认的构造器

public class Reflector {
  
  // 类的类型
  private final Class<?> type;
  // get 方法
  private final String[] readablePropertyNames;
  // set方法
  private final String[] writablePropertyNames;
  // set 方法名  执行该方法执行器
  private final Map<String, Invoker> setMethods = new HashMap<>();
  // get 方法名  执行该方法执行器
  private final Map<String, Invoker> getMethods = new HashMap<>();
  // set 参数名  参数类型
  private final Map<String, Class<?>> setTypes = new HashMap<>();
  // get 参数名  参数类型
  private final Map<String, Class<?>> getTypes = new HashMap<>();
  // get 默认的构造方法
  private Constructor<?> defaultConstructor;

  private Map<String, String> caseInsensitivePropertyMap = new HashMap<>();
  
  
  // 创建对象
  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()]);
    for (String propName : readablePropertyNames) {
      caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
    }
    for (String propName : writablePropertyNames) {
      caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
    }
  }
.............................................
....................................
}

Invoker

org.apache.ibatis.reflection.invoker.Invoker

public interface Invoker {

  // /调用方法
  Object invoke(Object target, Object[] args) throws IllegalAccessException, InvocationTargetException;

  // 获取类型
  Class<?> getType();
}

GetFieldInvoker
获取属性
org.apache.ibatis.reflection.invoker.*

public class GetFieldInvoker implements Invoker {
  private final Field field;

  public GetFieldInvoker(Field field) {
    this.field = field;
  }
  
  @Override
  public Object invoke(Object target, Object[] args) throws IllegalAccessException {
    try {
      return field.get(target);
    } catch (IllegalAccessException e) {
      if (Reflector.canControlMemberAccessible()) {
        field.setAccessible(true);
        return field.get(target);
      } else {
        throw e;
      }
    }
  }

  @Override
  public Class<?> getType() {
    return field.getType();
  }
}

org.apache.ibatis.reflection.invoker.MethodInvoker

public class MethodInvoker implements Invoker {

  private final Class<?> type;
  private final Method method;

  public MethodInvoker(Method method) {
    this.method = method;

    if (method.getParameterTypes().length == 1) {
      type = method.getParameterTypes()[0];
    } else {
      type = method.getReturnType();
    }
  }
// 执行方法调用
  @Override
  public Object invoke(Object target, Object[] args) throws IllegalAccessException, InvocationTargetException {
    try {
      return method.invoke(target, args);
    } catch (IllegalAccessException e) {
      if (Reflector.canControlMemberAccessible()) {
        method.setAccessible(true);
        return method.invoke(target, args);
      } else {
        throw e;
      }
    }
  }

  @Override
  public Class<?> getType() {
    return type;
  }
}

public class SetFieldInvoker implements Invoker {
  private final Field field;

  public SetFieldInvoker(Field field) {
    this.field = field;
  }
// 属性赋值操作
  @Override
  public Object invoke(Object target, Object[] args) throws IllegalAccessException {
    try {
      field.set(target, args[0]);
    } catch (IllegalAccessException e) {
      if (Reflector.canControlMemberAccessible()) {
        field.setAccessible(true);
        field.set(target, args[0]);
      } else {
        throw e;
      }
    }
    return null;
  }

  @Override
  public Class<?> getType() {
    return field.getType();
  }
}

Property

org.apache.ibatis.reflection.property.PropertyNamer

public final class PropertyNamer {

  private PropertyNamer() {
    // Prevent Instantiation of Static Class
  }


  //这个方法把访问方法的名字转换成范围属性的方式，先截取了get和set再将首字母变成小写。
  public static String methodToProperty(String name) {
    if (name.startsWith("is")) {
      name = name.substring(2);
    } else if (name.startsWith("get") || name.startsWith("set")) {
      name = name.substring(3);
    } else {
      throw new ReflectionException("Error parsing property name '" + name + "'.  Didn't start with 'is', 'get' or 'set'.");
    }

    if (name.length() == 1 || (name.length() > 1 && !Character.isUpperCase(name.charAt(1)))) {
      name = name.substring(0, 1).toLowerCase(Locale.ENGLISH) + name.substring(1);
    }

    return name;
  }

  public static boolean isProperty(String name) {
    return name.startsWith("get") || name.startsWith("set") || name.startsWith("is");
  }

  public static boolean isGetter(String name) {
    return name.startsWith("get") || name.startsWith("is");
  }

  public static boolean isSetter(String name) {
    return name.startsWith("set");
  }

}

public final class PropertyCopier {

  private PropertyCopier() {
    // Prevent Instantiation of Static Class
  }
  // 一个静态方法，复制属性，包括它的父类
  public static void copyBeanProperties(Class<?> type, Object sourceBean, Object destinationBean) {
    Class<?> parent = type;
    while (parent != null) {
      final Field[] fields = parent.getDeclaredFields();
      for (Field field : fields) {
        try {
          try {
            field.set(destinationBean, field.get(sourceBean));
          } catch (IllegalAccessException e) {
            if (Reflector.canControlMemberAccessible()) {
              field.setAccessible(true);
              field.set(destinationBean, field.get(sourceBean));
            } else {
              throw e;
            }
          }
        } catch (Exception e) {
          // Nothing useful to do, will only fail on final fields, which will be ignored.
        }
      }
      parent = parent.getSuperclass();
    }
  }

}

org.apache.ibatis.reflection.property.PropertyTokenizer

public class PropertyTokenizer implements Iterator<PropertyTokenizer> {
  private String name;
  private final String indexedName;
  private String index;
  private final String children;

  public PropertyTokenizer(String fullname) {
    // 
    int delim = fullname.indexOf('.');
    if (delim > -1) {
      name = fullname.substring(0, delim);
      children = fullname.substring(delim + 1);
    } else {
      name = fullname;
      children = null;
    }
    indexedName = name;
    delim = name.indexOf('[');
    if (delim > -1) {
      index = name.substring(delim + 1, name.length() - 1);
      name = name.substring(0, delim);
    }
  }

  public String getName() {
    return name;
  }

  public String getIndex() {
    return index;
  }

  public String getIndexedName() {
    return indexedName;
  }

  public String getChildren() {
    return children;
  }

  @Override
  public boolean hasNext() {
    return children != null;
  }

  @Override
  public PropertyTokenizer next() {
    return new PropertyTokenizer(children);
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException("Remove is not supported, as it has no meaning in the context of properties.");
  }
}

wrapper

org.apache.ibatis.reflection.wrapper.ObjectWrapper

public interface ObjectWrapper {

  //获取属性的值
  Object get(PropertyTokenizer prop);

  //设置属性的值
  void set(PropertyTokenizer prop, Object value);

  //查找某属性
  String findProperty(String name, boolean useCamelCaseMapping);

  //获取所有get的名字
  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);

  boolean isCollection();

  void add(Object element);

  <E> void addAll(List<E> element);

org.apache.ibatis.reflection.wrapper.BeanWrapper

public class BeanWrapper extends BaseWrapper {

  private final Object object;
  private final MetaClass metaClass;


  //构造函数
  public BeanWrapper(MetaObject metaObject, Object object) {
    super(metaObject);
    this.object = object;
    this.metaClass = MetaClass.forClass(object.getClass(), metaObject.getReflectorFactory());
  }

  //获取属性值
  @Override
  public Object get(PropertyTokenizer prop) {
    //根据prop.getIndex判断是否一个一个集合
    if (prop.getIndex() != null) {
      // 下面调用的是BaseWrapper的方法
      Object collection = resolveCollection(prop, object);
      return getCollectionValue(prop, collection);
    } else {
      return getBeanProperty(prop, object);
    }
  }

  //设置属性的值
  @Override
  public void set(PropertyTokenizer prop, Object value) {
    //根据prop.getIndex判断是否一个一个集合
    if (prop.getIndex() != null) {
      Object collection = resolveCollection(prop, object);
      //下面调用的是BaseWrapper的方法
      setCollectionValue(prop, collection, value);
    } else {
      setBeanProperty(prop, object, value);
    }
  }

  @Override
  public String findProperty(String name, boolean useCamelCaseMapping) {
    return metaClass.findProperty(name, useCamelCaseMapping);
  }

  @Override
  public String[] getGetterNames() {
    return metaClass.getGetterNames();
  }

  @Override
  public String[] getSetterNames() {
    return metaClass.getSetterNames();
  }

  @Override
  public Class<?> getSetterType(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());
      if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
        return metaClass.getSetterType(name);
      } else {
        return metaValue.getSetterType(prop.getChildren());
      }
    } else {
      return metaClass.getSetterType(name);
    }
  }

  @Override
  public Class<?> getGetterType(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());
      if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
        return metaClass.getGetterType(name);
      } else {
        return metaValue.getGetterType(prop.getChildren());
      }
    } else {
      return metaClass.getGetterType(name);
    }
  }

  @Override
  public boolean hasSetter(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      if (metaClass.hasSetter(prop.getIndexedName())) {
        MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());
        if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
          return metaClass.hasSetter(name);
        } else {
          return metaValue.hasSetter(prop.getChildren());
        }
      } else {
        return false;
      }
    } else {
      return metaClass.hasSetter(name);
    }
  }

  @Override
  public boolean hasGetter(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      if (metaClass.hasGetter(prop.getIndexedName())) {
        MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());
        if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
          return metaClass.hasGetter(name);
        } else {
          return metaValue.hasGetter(prop.getChildren());
        }
      } else {
        return false;
      }
    } else {
      return metaClass.hasGetter(name);
    }
  }

  @Override
  public MetaObject instantiatePropertyValue(String name, PropertyTokenizer prop, ObjectFactory objectFactory) {
    MetaObject metaValue;
    Class<?> type = getSetterType(prop.getName());
    try {
      Object newObject = objectFactory.create(type);
      metaValue = MetaObject.forObject(newObject, metaObject.getObjectFactory(), metaObject.getObjectWrapperFactory(), metaObject.getReflectorFactory());
      set(prop, newObject);
    } catch (Exception e) {
      throw new ReflectionException("Cannot set value of property '" + name + "' because '" + name + "' is null and cannot be instantiated on instance of " + type.getName() + ". Cause:" + e.toString(), e);
    }
    return metaValue;
  }

  private Object getBeanProperty(PropertyTokenizer prop, Object object) {
    try {
      Invoker method = metaClass.getGetInvoker(prop.getName());
      try {
        return method.invoke(object, NO_ARGUMENTS);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    } catch (RuntimeException e) {
      throw e;
    } catch (Throwable t) {
      throw new ReflectionException("Could not get property '" + prop.getName() + "' from " + object.getClass() + ".  Cause: " + t.toString(), t);
    }
  }

  private void setBeanProperty(PropertyTokenizer prop, Object object, Object value) {
    try {
      Invoker method = metaClass.getSetInvoker(prop.getName());
      Object[] params = {value};
      try {
        method.invoke(object, params);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    } catch (Throwable t) {
      throw new ReflectionException("Could not set property '" + prop.getName() + "' of '" + object.getClass() + "' with value '" + value + "' Cause: " + t.toString(), t);
    }
  }

  @Override
  public boolean isCollection() {
    return false;
  }

  @Override
  public void add(Object element) {
    throw new UnsupportedOperationException();
  }

  @Override
  public <E> void addAll(List<E> list) {
    throw new UnsupportedOperationException();
  }
}