Spring：使用@Value注释时，Bean无法从外部属性文件中读取值

Question

XML配置

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">

    <util:properties id="mongoProperties" location="file:///storage/local.properties" />

    <bean id="mongoService" class="com.business.persist.MongoService"></bean>
</beans>

和MongoService看起来像

@Service
public class MongoService {

    @Value("#{mongoProperties[host]}")
    private String host;

    @Value("#{mongoProperties[port]}")
    private int port;

    @Value("#{mongoProperties[database]}")
    private String database;

    private Mongo mongo;

    private static final Logger LOGGER = LoggerFactory.getLogger(MongoService.class);

    public MongoService() throws UnknownHostException {
        LOGGER.info("host=" + host + ", port=" + port + ", database=" + database);
        mongo = new Mongo(host, port);
    }

    public void putDocument(@Nonnull final DBObject document) {
        LOGGER.info("inserting document - " + document.toString());
        mongo.getDB(database).getCollection(getCollectionName(document)).insert(document, WriteConcern.SAFE);
    }

我写我的MongoServiceTest为

public class MongoServiceTest {

    @Autowired
    private MongoService mongoService;

    public MongoServiceTest() throws UnknownHostException {
        mongoRule = new MongoRule();
    }

    @Test
    public void testMongoService() {
        final DBObject document = DBContract.getUniqueQuery("001");
        document.put(DBContract.RVARIABLES, "values");
        document.put(DBContract.PVARIABLES, "values");

        mongoService.putDocument(document);
    }

我认为测试失败

12:37:25.224 [main] INFO  c.s.business.persist.MongoService - host=null, port=0, database=null
java.lang.NullPointerException
    at com.business.persist.MongoServiceTest.testMongoService(MongoServiceTest.java:40)

这意味着Bean无法从local.properties中读取值

local.properties

### === MongoDB interaction === ###
host="127.0.0.1"
port=27017
database=contract

我该如何解决？

更新即使在为字段创建了setters / getters之后，似乎也没有读取值。 我现在真的很笨。

更新01

在添加init（）方法并将其添加到bean之后，它的stil不起作用。 我什至都看不到日志消息
XML格式

<bean id="mongoService" class="com.business.persist.MongoService" init-method="init"></bean>

MongoService

@Service
public class MongoService {

    @Value("#{mongoProperties['host']}")
    private String host;

    @Value("#{mongoProperties['port']}")
    private int port;

    @Value("#{mongoProperties['database']}")
    private String database;

    private Mongo mongo;

    private static final Logger LOGGER = LoggerFactory.getLogger(MongoService.class);

    public MongoService() {}

    public void init() throws UnknownHostException {
        LOGGER.info("host=" + host + ", port=" + port + ", database=" + database);
        mongo = new Mongo(host, port);
    }

    public void putDocument(@Nonnull final DBObject document) {
        LOGGER.info("inserting document - " + document.toString());
        mongo.getDB(database).getCollection(getCollectionName(document)).insert(document, WriteConcern.SAFE);
    }

我该如何调试这个问题？

非常感谢！

Answer 1

我在这里看到一个问题，您正在MongoService构造函数中实例化Mongo类，但是此时您的属性尚未基于local.properties文件注入，因此host，port和database的值将为null 。

相反，您可以做的是不实例化Service构造函数中的Mongo类，让属性按照您执行的方式注入到MongoService中，然后将其创建为init方法的一部分，该方法在设置属性后被调用：

在MongoService中：

public void init(){
    mongo = new Mongo(host, port);
}

并在您的bean配置中：

<bean id="mongoService" class="com.business.persist.MongoService" init-method="init"></bean>