mybatis之MetaObject

MetaObject

元数据对象，底层肯定是反射，通过反射来进行设置值。

这个可以来操作对象中的属性，哪怕是组合方式，无论有多少层，这个都可以来进行操作。

举例如下所示：

public class Author implements Serializable {
    private static final long serialVersionUID = 1L;
    private Integer id;
    private List<String> hobbies;
    private Boolean flag;
    private Map<String,Object> objectMap;

    @Override
    public String toString() {
        return "Author{" +
                "id=" + id +
                ", hobbies=" + hobbies +
                ", flag=" + flag +
                ", objectMap=" + objectMap +
                '}';
    }
}

public class UserInfo implements Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    private Author author;

    @Override
    public String toString() {
        return "UserInfo{" +
                "name='" + name + '\'' +
                ", author=" + author +
                '}';
    }
}

MetaObject来进行演示：

直接给属性赋值

@Test
public void testOne(){
    UserInfo userInfo = new UserInfo();
    MetaObject metaObject =  MetaObject.forObject(userInfo, SystemMetaObject.DEFAULT_OBJECT_FACTORY,SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,SystemMetaObject.NULL_META_OBJECT.getReflectorFactory());
    metaObject.setValue("author.id",666);
    System.out.println(userInfo);
}

输出结果：

UserInfo{name='null', author=Author{id=666, hobbies=null, flag=null, objectMap=null}}

即使没有创建对象，但是使用MetaObject，也能够帮我们来创建这个类中的类的对象。

根据驼峰命名来查找得到对应的属性

@Test
public void testTwo(){
    UserInfo userInfo = new UserInfo();
    MetaObject metaObject =  MetaObject.forObject(userInfo, SystemMetaObject.DEFAULT_OBJECT_FACTORY,SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,SystemMetaObject.NULL_META_OBJECT.getReflectorFactory());
    // 支持驼峰命名
    String objectMmap = metaObject.findProperty("author.object_map", true);
    System.out.println(objectMmap);
}

对应输出：

author.objectMap

操作子属性中的数组

@Test
public void testFour(){
    UserInfo userInfo = new UserInfo();
    MetaObject metaObject =  MetaObject.forObject(userInfo, SystemMetaObject.DEFAULT_OBJECT_FACTORY,SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,SystemMetaObject.NULL_META_OBJECT.getReflectorFactory());
    ArrayList<String> strings = new ArrayList<>();
    strings.add("666");
    strings.add("777");
    strings.add("888");
    metaObject.setValue("author.hobbies",strings);
    System.out.println(metaObject.getValue("author.hobbies[2]"));
}

输出：

888

操作子属性中的map

@Test
public void testThree(){
    UserInfo userInfo = new UserInfo();
    MetaObject metaObject =  MetaObject.forObject(userInfo, SystemMetaObject.DEFAULT_OBJECT_FACTORY,SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,SystemMetaObject.NULL_META_OBJECT.getReflectorFactory());
    HashMap<String, Object> stringObjectHashMap = new HashMap<>();
    stringObjectHashMap.put("hello",777);
    stringObjectHashMap.put("world",888);
    metaObject.setValue("author.objectMap",stringObjectHashMap);
    System.out.println(metaObject.getValue("author.objectMap[hello]"));
}

打印：

777