@Value 在我的 springboot 项目中不起作用

Question

我在使用@Value 将值注入“appliction.properties”时遇到了麻烦。我创建了一个新的 SpringBoot 项目，并在“application.properties”文件中分析了一些属性。但是应用程序无法启动，因为“dataSource”bean 没有成功创建。调试后，我发现 'application.properties' 中的属性没有按预期加载。

配置类

@Configuration
public class SpringConfiguration {
    @Value("${spring.datasource.url}")
    private String url;
    @Value("${spring.datasource.driverClassName}")
    private String driverClassName;
    @Value("${spring.datasource.username}")
    private String username;
    @Value("${spring.datasource.password}")
    private String password;

    @Bean("dataSource")
    @ConfigurationProperties(prefix = "spring.datasource")
    public DataSource dataSource(DataSourceProperties properties) {
        return DataSourceBuilder.create()
                .type(HikariDataSource.class)
                .driverClassName(driverClassName)
                .url(url)
                .username(username)
                .password(password)
                .build();
    }

    @Bean
    public SqlSessionFactoryBean sqlSessionFactory(DataSource dataSource){
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(dataSource);
        return sqlSessionFactoryBean;
    }
}

application.properties

spring.data.mongodb.uri=mongodb://localhost.27017
spring.data.mongodb.database=test

spring.datasource.driverClassName=com.mysql.cj.jdbc.Driver
spring.datasource.password=123
spring.datasource.username=root
spring.datasource.url=jdbc:mysql://localhost:3306/common_test

堆栈跟踪的一部分

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'dataSourceScriptDatabaseInitializer' defined in class path resource [org/springframework/boot/autoconfigure/sql/init/DataSourceInitializationConfiguration.class]: Unsatisfied dependency expressed through method 'dataSourceScriptDatabaseInitializer' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [com/ty/SpringConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:800) ~[spring-beans-5.3.8.jar:5.3.8]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:541) ~[spring-beans-5.3.8.jar:5.3.8]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1334) ~[spring-beans-5.3.8.jar:5.3.8]
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.3.8.jar:5.3.8]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:653) ~[spring-beans-5.3.8.jar:5.3.8]
    ... 102 common frames omitted
Caused by: java.lang.NullPointerException: null
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:325) ~[na:1.8.0_191]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_191]
    at com.zaxxer.hikari.HikariConfig.attemptFromContextLoader(HikariConfig.java:970) ~[HikariCP-4.0.3.jar:na]
    at com.zaxxer.hikari.HikariConfig.setDriverClassName(HikariConfig.java:480) ~[HikariCP-4.0.3.jar:na]
    at org.springframework.boot.jdbc.DataSourceBuilder$MappedDataSourceProperty.set(DataSourceBuilder.java:460) ~[spring-boot-2.5.1.jar:2.5.1]
    at org.springframework.boot.jdbc.DataSourceBuilder$MappedDataSourceProperties.set(DataSourceBuilder.java:355) ~[spring-boot-2.5.1.jar:2.5.1]
    at org.springframework.boot.jdbc.DataSourceBuilder.build(DataSourceBuilder.java:190) ~[spring-boot-2.5.1.jar:2.5.1]
    at com.ty.SpringConfiguration.dataSource(SpringConfiguration.java:35) ~[classes/:na]

debug scene application.properties

pom.xml

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.ty</groupId>
    <artifactId>common-test</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>common-test</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-mongodb</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-spring</artifactId>
            <version>1.2.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.9</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.3.0</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.9.0</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

Answer 1

ok 首先这不是@Value 注释的问题。如果您已经在使用@ConfigurationProperties(prefix = "spring.datasource")，那么您不需要使用@Value 注释。 ii 会自动为你配置所有的属性。 您可以像这样简单地创建数据源 bean。确保您在 pom.xml 中有所需的依赖项。

@Bean("mysqldataSource")
@ConfigurationProperties(prefix = "spring.datasource")
public DataSource dataSource() {
    return DataSourceBuilder.create().build();
        
}

Answer 2

添加这个注解@PropertySource(value = "application.properties")

@Configuration
@PropertySource(value = "application.properties")
public class SpringConfiguration {
    @Value("${spring.datasource.url}")
    private String url;
    @Value("${spring.datasource.driverClassName}")
    private String driverClassName;
    @Value("${spring.datasource.username}")
    private String username;
    @Value("${spring.datasource.password}")
    private String password;

    @Bean("dataSource")
    @ConfigurationProperties(prefix = "spring.datasource")
    public DataSource dataSource(DataSourceProperties properties) {
        return DataSourceBuilder.create()
                .type(HikariDataSource.class)
                .driverClassName(driverClassName)
                .url(url)
                .username(username)
                .password(password)
                .build();
    }

    @Bean
    public SqlSessionFactoryBean sqlSessionFactory(DataSource dataSource){
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(dataSource);
        return sqlSessionFactoryBean;
    }
}