使用显式模板的SpringBoot mongo配置无法启动

<dependencies>
    <!-- Spring Boot Starter -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <!-- MongoDB Driver -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-mongodb</artifactId>
    </dependency>
</dependencies>

spring.data.mongodb.host=localhost
spring.data.mongodb.port=27017
spring.data.mongodb.database=mydatabase

@Configuration
public class MongoConfig {

    @Value("${spring.data.mongodb.host}")
    private String host;

    @Value("${spring.data.mongodb.port}")
    private int port;

    @Value("${spring.data.mongodb.database}")
    private String database;

    @Bean
    public MongoTemplate mongoTemplate() throws Exception {
        MongoClient mongoClient = new MongoClient(host, port);
        MongoTemplate mongoTemplate = new MongoTemplate(mongoClient, database);
        return mongoTemplate;
    }
}