Question

我正在尝试使用spring开发rest代码。

@RestController
public class MongoController {

    @Autowired
    private MongoDAO mongoDAO ;

    @RequestMapping(value = "/mongotest", method = RequestMethod.GET)
    public String creatTest() {

        return " YO Mongo";
    }


}

我的MongoDAO课程如下所示

@Service("mongoDAO")
@Component
public class MongoDAO {


    @Resource
    private DBCollection user ;
    @Resource
    private MongoDatabase userDatabase;
    @Resource
    private MongoCollection<Document> usersCollection;
    @Resource
    private MongoClient mongoClient;

/*  public MongoDAO(final MongoDatabase userDatabase) {
        usersCollection = userDatabase.getCollection("user");
        MongoClient mongoClient = new MongoClient("localhost", 27017);
        DB db = mongoClient.getDB("ITAU");
        user = db.getCollection("user");
    }*/

    public MongoDAO(MongoDatabase userDatabase1) {
        usersCollection = userDatabase1.getCollection("user");

    }

    public MongoDAO() {
        usersCollection = userDatabase.getCollection("user");

    }

但我得到的错误是......

引起：org.springframework.beans.factory.BeanCreationException：创建在文件中定义名称为“mongoDAO”的bean时出错 [C：\用户\用户\桌面\ ITAU \ 77 \ ABC-iCOE-WAL \ ItauBankingTransac s \ rest-client \ target \ classes \ com \ ABC \ WAL \ itaudemo \ mongo \ dao \ MongoDAO.class]：bean的实例化失败;嵌套异常是 org.springframework.beans.BeanInstantiationException：可以吗？ nstantiate bean class [com.ABC.WAL.itaudemo.mongo.dao.MongoDAO]：构造函数抛出异常;嵌套异常是显示java.lang.NullPointerException 在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean（AbstractAutowireCapableBeanFactory.java:1076）

Answer 1

创建userDatabase bean后，字段MongoDao自动装配。如果您想在构建操作后执行一些操作，请尝试以下操作：

@Service("mongoDAO")
public class MongoDAO {


    @Resource
    private DBCollection user ;
    @Resource
    private MongoDatabase userDatabase;
    @Resource
    private MongoCollection<Document> usersCollection;
    @Resource
    private MongoClient mongoClient;

    public MongoDAO() {

    }

    @PostConstruct
    public postConstruct() {
        usersCollection = userDatabase.getCollection("user");

    }

可能会省略构造函数。通常，最好不要为组件类定制构造函数。

Answer 2

只需使用@Service("mongoDAO")，无需@Component

@Service("mongoDAO")
public class MongoDAO {

您可以使用两个注释中的任何一个，@ Service用于服务层代码以提高可读性。 @Component更像是一个通用的注释。

无法在Spring中初始化bean类

2 个答案: