MyBatis源码分析（六）MetaObject工具类的使用与源码分析

文章目录

• ​​一、MetaObject基本使用​​
• ​​二、关键类源码分析​​

• ​​1、MetaObject的构造方法​​
• ​​2、PropertyTokenizer分词器​​
• ​​3、BeanWrapper​​
• ​​4、MetaClass​​
• ​​5、DefaultReflectorFactory​​
• ​​6、Reflector​​
• ​​7、总结​​

• ​​三、MetaObject的getValue源码分析​​
• ​​写在后面​​

一、MetaObject基本使用

public class User {

    private int id;
    private String name;
    private String phoneNumber;
    private User child;
    List<User> users;
    private List<String> likes;
    Map<String, String> labels;

    // get set
}

Object user = new User();
Configuration configuration = new Configuration();
MetaObject metaObject = configuration.newMetaObject(user);
// 直接属性赋值
metaObject.setValue("name", "zhangsan");
System.out.println(metaObject.getValue("name"));

// 子属性赋值，对象为null会自动创建，并填充属性值
metaObject.setValue("child.name", "lisi");
System.out.println(metaObject.getValue("child.name"));

// 查找驼峰属性 phoneNumber
System.out.println(metaObject.findProperty("phone_number", true));

// 操作数组，基于索引操作数组
ArrayList<String> strings = new ArrayList<>();
strings.add("sing");
strings.add("run");
metaObject.setValue("likes", strings);
System.out.println(metaObject.getValue("likes"));
System.out.println(metaObject.getValue("likes[0]")); // 获取第一个

// 操作Map
metaObject.setValue("labels", new HashMap<String, String>());
metaObject.setValue("labels[red]", "like");
metaObject.setValue("labels[blue]", "notLike");
System.out.println(metaObject.getValue("labels"));
System.out.println(metaObject.getValue("labels[red]"));

MetaObject是一个强大的反射工具类，
支持查找属性（忽略大小写、支持驼峰、支持子属性）、
查找子属性（“user.name”、"users[0].id"获取集合中子属性的值、"user[name]"获取map）、
支持设置子属性（自动创建子属性，必须带有空参构造方法且不能是集合）。

MetaObject工具类不止设置、查找属性值，还提供了获取set、get方法、查找属性值等反射常用方法。

二、关键类源码分析

1、MetaObject的构造方法

调用MetaObject 的forObject方法，可以将Object对象转换成BeanWrapper对象，最终调用了new BeanWrapper

private MetaObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {
  this.originalObject = object;
  this.objectFactory = objectFactory;
  this.objectWrapperFactory = objectWrapperFactory;
  this.reflectorFactory = reflectorFactory;

  if (object instanceof ObjectWrapper) {
    this.objectWrapper = (ObjectWrapper) object;
  } else if (objectWrapperFactory.hasWrapperFor(object)) {
    this.objectWrapper = objectWrapperFactory.getWrapperFor(this, object);
  } else if (object instanceof Map) {
    this.objectWrapper = new MapWrapper(this, (Map) object);
  } else if (object instanceof Collection) {
    this.objectWrapper = new CollectionWrapper(this, (Collection) object);
  } else { // 普通类
    this.objectWrapper = new BeanWrapper(this, object);
  }
}

public static MetaObject forObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {
  if (object == null) {
    return SystemMetaObject.NULL_META_OBJECT;
  } else {
    return new MetaObject(object, objectFactory, objectWrapperFactory, reflectorFactory);
  }
}

2、PropertyTokenizer分词器

public class PropertyTokenizer implements Iterator<PropertyTokenizer> {
  private String name; // 属性名称
  private final String indexedName; // 带着索引的属性名称
  private String index; // 索引（如果有的话）
  private final String children; // 除了indexedName之外的剩余的表达式名称 

  // 构造方法，根据 . 来进行分词，分词完毕后会将以上四个属性初始化好
  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;
  }

  // 判断是否有子节点
  @Override
  public boolean hasNext() {
    return children != null;
  }

  // 创建子节点时，也是new一个PropertyTokenizer分词器，重复操作
  @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.");
  }
}

3、BeanWrapper

BeanWrapper的构造方法，将原始对象和metaObject对象进行存储，并调用MetaClass的forClass方法，解析Object原始对象的基本数据。

BeanWrapper中提供了获取Object原始对象的 设置值、获取值、获取getset方法、获取属性、获取setget类型等等一系列核心操作方法，最终都是委派给MetaClass 来实现的。

public class BeanWrapper extends BaseWrapper {

  private final Object object;
  private final MetaClass metaClass;

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

  @Override
  public Object get(PropertyTokenizer prop) {
    if (prop.getIndex() != null) {
      Object collection = resolveCollection(prop, object);
      return getCollectionValue(prop, collection);
    } else {
      return getBeanProperty(prop, object);
    }
  }

  @Override
  public void set(PropertyTokenizer prop, Object value) {
    if (prop.getIndex() != null) {
      Object collection = resolveCollection(prop, object);
      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();
  }

}

4、MetaClass

在MetaClass的构造方法中，通过ReflectorFactory反射工厂的findForClass，将原始的Object进行解析，最终将解析的结果存放到Reflector成员变量中。

在MetaClass的核心方法，大多数操作的底层都是操作Reflector来进行实现的。

public class MetaClass {

  private final ReflectorFactory reflectorFactory;
  private final Reflector reflector;

  private MetaClass(Class<?> type, ReflectorFactory reflectorFactory) {
    this.reflectorFactory = reflectorFactory;
    this.reflector = reflectorFactory.findForClass(type);
  }

  public static MetaClass forClass(Class<?> type, ReflectorFactory reflectorFactory) {
    return new MetaClass(type, reflectorFactory);
  }

  public MetaClass metaClassForProperty(String name) {
    Class<?> propType = reflector.getGetterType(name);
    return MetaClass.forClass(propType, reflectorFactory);
  }

  public String findProperty(String name) {
    StringBuilder prop = buildProperty(name, new StringBuilder());
    return prop.length() > 0 ? prop.toString() : null;
  }

  public String findProperty(String name, boolean useCamelCaseMapping) {
    if (useCamelCaseMapping) {
      name = name.replace("_", "");
    }
    return findProperty(name);
  }

  public String[] getGetterNames() {
    return reflector.getGetablePropertyNames();
  }

  public String[] getSetterNames() {
    return reflector.getSetablePropertyNames();
  }

  public Class<?> getSetterType(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      MetaClass metaProp = metaClassForProperty(prop.getName());
      return metaProp.getSetterType(prop.getChildren());
    } else {
      return reflector.getSetterType(prop.getName());
    }
  }

  public Class<?> getGetterType(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      MetaClass metaProp = metaClassForProperty(prop);
      return metaProp.getGetterType(prop.getChildren());
    }
    // issue #506. Resolve the type inside a Collection Object
    return getGetterType(prop);
  }

  private MetaClass metaClassForProperty(PropertyTokenizer prop) {
    Class<?> propType = getGetterType(prop);
    return MetaClass.forClass(propType, reflectorFactory);
  }

  private Class<?> getGetterType(PropertyTokenizer prop) {
    Class<?> type = reflector.getGetterType(prop.getName());
    if (prop.getIndex() != null && Collection.class.isAssignableFrom(type)) {
      Type returnType = getGenericGetterType(prop.getName());
      if (returnType instanceof ParameterizedType) {
        Type[] actualTypeArguments = ((ParameterizedType) returnType).getActualTypeArguments();
        if (actualTypeArguments != null && actualTypeArguments.length == 1) {
          returnType = actualTypeArguments[0];
          if (returnType instanceof Class) {
            type = (Class<?>) returnType;
          } else if (returnType instanceof ParameterizedType) {
            type = (Class<?>) ((ParameterizedType) returnType).getRawType();
          }
        }
      }
    }
    return type;
  }

  private Type getGenericGetterType(String propertyName) {
    try {
      Invoker invoker = reflector.getGetInvoker(propertyName);
      if (invoker instanceof MethodInvoker) {
        Field declaredMethod = MethodInvoker.class.getDeclaredField("method");
        declaredMethod.setAccessible(true);
        Method method = (Method) declaredMethod.get(invoker);
        return TypeParameterResolver.resolveReturnType(method, reflector.getType());
      } else if (invoker instanceof GetFieldInvoker) {
        Field declaredField = GetFieldInvoker.class.getDeclaredField("field");
        declaredField.setAccessible(true);
        Field field = (Field) declaredField.get(invoker);
        return TypeParameterResolver.resolveFieldType(field, reflector.getType());
      }
    } catch (NoSuchFieldException | IllegalAccessException e) {
      // Ignored
    }
    return null;
  }

  public boolean hasSetter(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      if (reflector.hasSetter(prop.getName())) {
        MetaClass metaProp = metaClassForProperty(prop.getName());
        return metaProp.hasSetter(prop.getChildren());
      } else {
        return false;
      }
    } else {
      return reflector.hasSetter(prop.getName());
    }
  }

  public boolean hasGetter(String name) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      if (reflector.hasGetter(prop.getName())) {
        MetaClass metaProp = metaClassForProperty(prop);
        return metaProp.hasGetter(prop.getChildren());
      } else {
        return false;
      }
    } else {
      return reflector.hasGetter(prop.getName());
    }
  }

  public Invoker getGetInvoker(String name) {
    return reflector.getGetInvoker(name);
  }

  public Invoker getSetInvoker(String name) {
    return reflector.getSetInvoker(name);
  }

  private StringBuilder buildProperty(String name, StringBuilder builder) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      String propertyName = reflector.findPropertyName(prop.getName());
      if (propertyName != null) {
        builder.append(propertyName);
        builder.append(".");
        MetaClass metaProp = metaClassForProperty(propertyName);
        metaProp.buildProperty(prop.getChildren(), builder);
      }
    } else {
      String propertyName = reflector.findPropertyName(name);
      if (propertyName != null) {
        builder.append(propertyName);
      }
    }
    return builder;
  }

  public boolean hasDefaultConstructor() {
    return reflector.hasDefaultConstructor();
  }

}

5、DefaultReflectorFactory

DefaultReflectorFactory实现了ReflectorFactory，用于生成Reflector

public class DefaultReflectorFactory implements ReflectorFactory {
  private boolean classCacheEnabled = true;
  private final ConcurrentMap<Class<?>, Reflector> reflectorMap = new ConcurrentHashMap<>();

  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
      return MapUtil.computeIfAbsent(reflectorMap, type, Reflector::new);
    } else {
      return new Reflector(type);
    }
  }

}

6、Reflector

这是MyBatis的反射最底层类，构造方法中将原始的对象Class进行解析，所有的方法、属性等等都存放到这里用于存储。

public class Reflector {

  private final Class<?> type;
  private final String[] readablePropertyNames;
  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<>();

  public Reflector(Class<?> clazz) {
    type = clazz;
    addDefaultConstructor(clazz);
    addGetMethods(clazz);
    addSetMethods(clazz);
    addFields(clazz);
    readablePropertyNames = getMethods.keySet().toArray(new String[0]);
    writablePropertyNames = setMethods.keySet().toArray(new String[0]);
    for (String propName : readablePropertyNames) {
      caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
    }
    for (String propName : writablePropertyNames) {
      caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
    }
  }

  private void addDefaultConstructor(Class<?> clazz) {
    Constructor<?>[] constructors = clazz.getDeclaredConstructors();
    Arrays.stream(constructors).filter(constructor -> constructor.getParameterTypes().length == 0)
      .findAny().ifPresent(constructor -> this.defaultConstructor = constructor);
  }

  private void addGetMethods(Class<?> clazz) {
    Map<String, List<Method>> conflictingGetters = new HashMap<>();
    Method[] methods = getClassMethods(clazz);
    Arrays.stream(methods).filter(m -> m.getParameterTypes().length == 0 && PropertyNamer.isGetter(m.getName()))
      .forEach(m -> addMethodConflict(conflictingGetters, PropertyNamer.methodToProperty(m.getName()), m));
    resolveGetterConflicts(conflictingGetters);
  }

  private void resolveGetterConflicts(Map<String, List<Method>> conflictingGetters) {
    for (Entry<String, List<Method>> entry : conflictingGetters.entrySet()) {
      Method winner = null;
      String propName = entry.getKey();
      boolean isAmbiguous = false;
      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)) {
            isAmbiguous = true;
            break;
          } 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 {
          isAmbiguous = true;
          break;
        }
      }
      addGetMethod(propName, winner, isAmbiguous);
    }
  }

  private void addGetMethod(String name, Method method, boolean isAmbiguous) {
    MethodInvoker invoker = isAmbiguous
        ? new AmbiguousMethodInvoker(method, MessageFormat.format(
            "Illegal overloaded getter method with ambiguous type for property ''{0}'' in class ''{1}''. This breaks the JavaBeans specification and can cause unpredictable results.",
            name, method.getDeclaringClass().getName()))
        : new MethodInvoker(method);
    getMethods.put(name, invoker);
    Type returnType = TypeParameterResolver.resolveReturnType(method, type);
    getTypes.put(name, typeToClass(returnType));
  }

  private void addSetMethods(Class<?> clazz) {
    Map<String, List<Method>> conflictingSetters = new HashMap<>();
    Method[] methods = getClassMethods(clazz);
    Arrays.stream(methods).filter(m -> m.getParameterTypes().length == 1 && PropertyNamer.isSetter(m.getName()))
      .forEach(m -> addMethodConflict(conflictingSetters, PropertyNamer.methodToProperty(m.getName()), m));
    resolveSetterConflicts(conflictingSetters);
  }

  private void addMethodConflict(Map<String, List<Method>> conflictingMethods, String name, Method method) {
    if (isValidPropertyName(name)) {
      List<Method> list = MapUtil.computeIfAbsent(conflictingMethods, name, k -> new ArrayList<>());
      list.add(method);
    }
  }

  private void resolveSetterConflicts(Map<String, List<Method>> conflictingSetters) {
    for (Entry<String, List<Method>> entry : conflictingSetters.entrySet()) {
      String propName = entry.getKey();
      List<Method> setters = entry.getValue();
      Class<?> getterType = getTypes.get(propName);
      boolean isGetterAmbiguous = getMethods.get(propName) instanceof AmbiguousMethodInvoker;
      boolean isSetterAmbiguous = false;
      Method match = null;
      for (Method setter : setters) {
        if (!isGetterAmbiguous && setter.getParameterTypes()[0].equals(getterType)) {
          // should be the best match
          match = setter;
          break;
        }
        if (!isSetterAmbiguous) {
          match = pickBetterSetter(match, setter, propName);
          isSetterAmbiguous = match == null;
        }
      }
      if (match != null) {
        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;
    }
    MethodInvoker invoker = new AmbiguousMethodInvoker(setter1,
        MessageFormat.format(
            "Ambiguous setters defined for property ''{0}'' in class ''{1}'' with types ''{2}'' and ''{3}''.",
            property, setter2.getDeclaringClass().getName(), paramType1.getName(), paramType2.getName()));
    setMethods.put(property, invoker);
    Type[] paramTypes = TypeParameterResolver.resolveParamTypes(setter1, type);
    setTypes.put(property, typeToClass(paramTypes[0]));
    return null;
  }

  private void addSetMethod(String name, Method method) {
    MethodInvoker invoker = new MethodInvoker(method);
    setMethods.put(name, invoker);
    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;
  }

  private void addFields(Class<?> clazz) {
    Field[] fields = clazz.getDeclaredFields();
    for (Field field : fields) {
      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.
   *
   * @param clazz The class
   * @return An array containing all methods in this class
   */
  private Method[] getClassMethods(Class<?> clazz) {
    Map<String, Method> uniqueMethods = new HashMap<>();
    Class<?> currentClass = clazz;
    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[0]);
  }

  private void addUniqueMethods(Map<String, Method> uniqueMethods, Method[] methods) {
    for (Method currentMethod : methods) {
      if (!currentMethod.isBridge()) {
        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++) {
      sb.append(i == 0 ? ':' : ',').append(parameters[i].getName());
    }
    return sb.toString();
  }

  /**
   * 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;
  }

  /**
   * 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.containsKey(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.containsKey(propertyName);
  }

  public String findPropertyName(String name) {
    return caseInsensitivePropertyMap.get(name.toUpperCase(Locale.ENGLISH));
  }
}

7、总结

MyBatis的MetaObject反射工具类，可以说是MyBatis的底层类，几乎不与MyBatis有耦合，如果项目中也需要这样一个工具类，可以“拿来即用”，或者稍加修改就可以拿来使用。非常强大。

（图片来自于鲁班大叔）

三、MetaObject的getValue源码分析

我们以这样一个表达式为例，进行源码分析：

// 获取对象中users的第一个元素中的child属性中的name属性
metaObject.getValue("users[0].child.name");

MetaObject的getValue核心源码：

// org.apache.ibatis.reflection.MetaObject#getValue
public Object getValue(String name) {
  // 创建属性分词器，将users[0].child.name，创建一个name=users;indexedName=users[0];index=0;children=child.name的分词器
  PropertyTokenizer prop = new PropertyTokenizer(name); 
  if (prop.hasNext()) { // 是否有下一个子节点
    MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());// 继续构造一个MetaObject，对象是users[0]
    if (metaValue == SystemMetaObject.NULL_META_OBJECT) { // 如果是null，直接返回
      return null;
    } else { // 如果不是null，就递归调用getValue方法，直到查找到最后一个属性
      return metaValue.getValue(prop.getChildren()); 
    }
  } else { // 如果没有子节点，通过反射调用get方法获取属性
    return objectWrapper.get(prop);
  }
}

写在后面

如果本文对你有帮助，请点赞收藏关注一下吧 ~