在spring for mongodb中，会发现当一个pojo序列化为一个document时，会出现如下
情况： 

public class User {

  String username;
  String password;


}


转变为mongodb 时


MongoOperations mongoOperation = (MongoOperations)ctx.getBean("mongoTemplate"); 
    User user = new User("abc", "password123");
    mongoOperation.save(user, "users");


会发现document中，多了个_class属性：


{ 
  "_class" : "com.abc.user.User", 

  ...................
}


多了_class的意义，在下面这个链接有很好的解答：


​​http://stackoverflow.com/questions/6810488/spring-data-mongodb-mappingmongoconverter-remove-class/ ​​，其实就是说，为了在把document转换成Java对象时能够转换到具体的子类.


要去掉的方法简单：DefaultMongoTypeMapper类的构造函数的第一个参数是Type在MongoDB中名字. 设置为null的话就不会在保存时自动添加_class属性.所以需要覆写



MappingMongoConverter。


1）用注解的方法取消：


@Configuration
public class SpringMongoConfig{

  public @Bean
  MongoDbFactory mongoDbFactory() throws Exception {
	return new SimpleMongoDbFactory(new Mongo(), "database");
  }

  public @Bean
  MongoTemplate mongoTemplate() throws Exception {


	MappingMongoConverter converter = 
		new MappingMongoConverter(mongoDbFactory(), new MongoMappingContext());
	converter.setTypeMapper(new DefaultMongoTypeMapper(null));

	MongoTemplate mongoTemplate = new MongoTemplate(mongoDbFactory(), converter);

	return mongoTemplate;

  }

2）XML配置文件
   [code="java"]
<mongo:mongo host="localhost" port="27017" />
<mongo:db-factory dbname="database" />

 <bean id="mappingContext"
	class="org.springframework.data.mongodb.core.mapping.MongoMappingContext" />

 <bean id="defaultMongoTypeMapper"
	class="org.springframework.data.mongodb.core.convert.DefaultMongoTypeMapper">
	<constructor-arg name="typeKey"><null/></constructor-arg>
 </bean>

 <bean id="mappingMongoConverter"
	class="org.springframework.data.mongodb.core.convert.MappingMongoConverter">
	<constructor-arg name="mongoDbFactory" ref="mongoDbFactory" />
	<constructor-arg name="mappingContext" ref="mappingContext" />
	<property name="typeMapper" ref="defaultMongoTypeMapper" />
 </bean>

 <bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
	<constructor-arg name="mongoDbFactory" ref="mongoDbFactory" />
	<constructor-arg name="mongoConverter" ref="mappingMongoConverter" />
 </bean>