我正在嘗試創(chuàng)建一個(gè)可以由所有DAO擴(kuò)展的BaseDAO接口.該項(xiàng)目使用mongodb的spring-data.問題是,如果我讓所有單獨(dú)的DAO擴(kuò)展MongoRepository而不是編寫實(shí)現(xiàn)類,那么一切正常.但是如果我嘗試使用泛型將MongoRepository添加到BaseDAO接口,則該應(yīng)用程序不再起作用,因?yàn)閷?shí)例化SimpleMongoRepository所需的參數(shù)為null.這是我到目前為止的代碼：

BaseDAO.java

import com.test.mongodb.BaseEntity;
import org.springframework.data.mongodb.repository.MongoRepository;
import org.springframework.data.repository.NoRepositoryBean;

import java.io.Serializable;

@NoRepositoryBean
public interface BaseDAO<T extends BaseEntity, ID extends Serializable> extends         MongoRepository<T, ID> {
    public T getTestObject(ID id);
}

BaseDAOImpl.java

import com.test.mongodb.BaseEntity;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.repository.query.EntityInformationCreator;
import org.springframework.data.mongodb.repository.query.MongoEntityInformation;
import org.springframework.data.mongodb.repository.support.SimpleMongoRepository;
import org.springframework.data.repository.NoRepositoryBean;

import java.io.Serializable;

@NoRepositoryBean
public class BaseDAOImpl<T extends BaseEntity, ID extends Serializable> extends     SimpleMongoRepository<T,
        ID> implements BaseDAO<T, ID> {

    @Autowired
    private static MongoTemplate mongoTemplate;

    @Autowired
    private static EntityInformationCreator entityInformationCreator;

    public BaseDAOImpl(Class<T> type){
        super((MongoEntityInformation<T, ID>)     entityInformationCreator.getEntityInformation(type), mongoTemplate);
    }

    @Override
    public T getTestObject(ID id){
        return findOne(id);
    }
}

UserDAO.java

import com.test.mongodb.User;
import org.springframework.stereotype.Repository;

@Repository
public interface UserDAO extends BaseDAO<User, String> {}

UserDAOImpl.java

import com.test.mongodb.User;
import org.springframework.stereotype.Repository;

@Repository
public class UserDAOImpl extends BaseDAOImpl<User, String> implements UserDAO {

    public UserDAOImpl(){
        super(User.class);
    }
}

applicationContext.xml中

    <?xml version="1.0" encoding="UTF-8"?><beans xmlns:xsi="http://www./2001/XMLSchema-instance"
       xmlns="http://www./schema/beans"
       xmlns:mongo="http://www./schema/data/mongo"
       xsi:schemaLocation="http://www./schema/beans http://www./schema/beans/spring-beans-3.2.xsd
    http://www./schema/data/mongo http://www./schema/data/mongo/spring-mongo-1.1.xsd">

    <!-- MongoFactoryBean instance -->
    <mongo:mongo host="localhost" port="27017" />

    <mongo:db-factory dbname="bank" mongo-ref="mongo" />

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

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

    <bean id="entityInformationCreator" class="org.springframework.data.mongodb.repository.support.DefaultEntityInformationCreator">
        <constructor-arg name="mappingContext" ref="mappingContext" />
    </bean>
    <mongo:repositories base-package="com.test.mongodb.repo"/>
</beans>

App.java

public class App {

    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

        UserRepository userRepository = context.getBean("userRepository", UserRepository.class);

        User user = new User("Test User");

        userRepository.save(user);

        String id = user.getId();
        System.out.println(id);

        System.out.println(userRepository.getTestObject(user.getId()));
    }
}

因此,當(dāng)我運(yùn)行它時(shí),我在BaseDAOImpl中得到一個(gè)NPE,因?yàn)閙ongoTemplate和entityInformationCreator都是null.如何加載它們？我還查看了Spring MongoDB參考文檔,但它主要是說要遵循其他類型的存儲(chǔ)庫的文檔.我在那里和網(wǎng)上其他地方唯一能找到的就是創(chuàng)建一個(gè)工廠bean.所以我也試過了：

MongoRepoFactoryBean.java

import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.repository.MongoRepository;
import org.springframework.data.mongodb.repository.support.MongoRepositoryFactory;
import org.springframework.data.mongodb.repository.support.MongoRepositoryFactoryBean;
import org.springframework.data.repository.NoRepositoryBean;
import org.springframework.data.repository.core.support.RepositoryFactorySupport;

import java.io.Serializable;

@NoRepositoryBean
public class MongoRepoFactoryBean<T extends MongoRepository<?,?>, ID extends
    Serializable> extends MongoRepositoryFactoryBean {

    protected RepositoryFactorySupport createRepositoryFactory(Class<T> clazz, MongoTemplate mongoTemplate) {
        return new MongoRepoFactory(clazz, mongoTemplate);
    }

    private static class MongoRepoFactory extends MongoRepositoryFactory {
        private Class clazz;
        private MongoTemplate mongoTemplate;

        public MongoRepoFactory(Class clazz, MongoTemplate mongoTemplate) {
            super(mongoTemplate);
            this.mongoTemplate = mongoTemplate;
            this.clazz = clazz;
        }

        public Object getTargetRepository() {
            return new BaseDAOImpl(clazz);
        }

        public Class<?> getRepositoryBaseClass() {
            return BaseDAOImpl.class;
        }
    }
}

并使用以下命令更改了applicationContext.xml：

<mongo:repositories base-package="com.test.mongodb.repo"
                    factory-class="com.test.mongodb.repo.MongoRepoFactoryBean"/>

但這也不起作用.我也嘗試使用JavaConfig,但是在使用注釋進(jìn)行配置時(shí)我不知道如何設(shè)置工廠類.我究竟做錯(cuò)了什么？ SimpleMongoRepository沒有默認(rèn)構(gòu)造函數(shù).注入靜態(tài)字段有問題嗎？

解決方法:

參考文檔已過時(shí),未反映spring-data-mongodb 1.1.1.RELEASE的更改.

我和你有同樣的問題,這就是我解決它的方法.

請(qǐng)注意,我使用的是MongoConfig類和應(yīng)用程序上下文XML,但您確實(shí)不需要兩者,我只是決定這樣做來舉例說明它們的用法.

MongoConfig類:(你也可以通過spring app context XML來做到這一點(diǎn))

@Configuration
public class MongoConfig extends AbstractMongoConfiguration {
    @Override
    protected String getDatabaseName() {
        return "myDb";
    }

    @Override
    @Bean
    public Mongo mongo() throws Exception {
        return new Mongo("localhost");
    }
}

Spring App Context XML：

<!-- You can also expose the bean as a method in the MongoConfig class -->
<bean id="mongoRepositoryFactory" class="org.springframework.data.mongodb.repository.support.MongoRepositoryFactory">
    <!-- mongoTemplate comes from AbstractMongoConfiguration -->
    <constructor-arg ref="mongoTemplate" />
</bean>

<context:annotation-config />
<context:component-scan base-package="com.example.domain" />
<mongo:repositories base-package="com.example.domain.repository" mongo-template-ref="mongoTemplate" />

我的repository / dao類：

@Repository
public class MyBeanDao extends SimpleMongoRepository<MyBean, String> {

    public MyBeanDao(MongoEntityInformation<MyBean, String> metadata, MongoOperations mongoOperations) {
        super(metadata, mongoOperations);
    }

    @Autowired
    public MyBeanDao(MongoRepositoryFactory factory, MongoOperations mongoOperations) {
        this(factory.<MyBean, String>getEntityInformation(MyBean.class), mongoOperations);
    }

    ... // more stuff
}

我知道這真的很丑,只適用于Java 6,但由于getEntityInformation()的返回類型是完全無界限的,所以它或者ID類型是Serializable而不是你的實(shí)際ID類型,并且每次你都進(jìn)行顯式轉(zhuǎn)換需要它.

我希望有一個(gè)更清潔的方式,但我已經(jīng)看了很長一段時(shí)間通過API甚至源代碼,并沒有想出一個(gè)更好的方法來做到這一點(diǎn),而沒有提出你自己的一些彈簧數(shù)據(jù)的實(shí)現(xiàn)-mongodb課程.

希望能幫助到你.