java Spring Boot 不从属性文件中读取
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Spring Boot not reading from property file
提问by Sam
I have tried every option on web but not able to set the values in following method:
我已经尝试了网络上的每个选项，但无法在以下方法中设置值：
@Configuration
@PropertySource("classpath:application.properties")
public class MyDataSource {
@Value("${db.driver}")
private String DB_DRIVER;
@Value("${db.url}")
private String DB_URL;
@Value("${db.username}")
private String DB_USERNAME;
@Value("${db.password}")
private String DB_PASSWORD;
@Bean
public static PropertySourcesPlaceholderConfigurer placeHolderConfigurer() {
return new PropertySourcesPlaceholderConfigurer();
}
@Bean
public DataSource getDataSource() {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName(DB_DRIVER);
dataSource.setUrl(DB_URL);
dataSource.setUsername(DB_USERNAME);
dataSource.setPassword(DB_PASSWORD);
return dataSource;
}
}
My application.propertiesis in main/resourcesfolder and values can be seen in variables in debug mode. But on running app, it shows Property ' ' must not be empty.
Myapplication.properties在main/resources文件夹中，值可以在调试模式下的变量中看到。但是在运行应用程序时，它显示Property ' ' must not be empty.
EDIT: I am not sure what can be the issue in first case? So changed the application.property file as suggested and code as below :
编辑：我不确定在第一种情况下会出现什么问题？因此，按照建议更改了 application.property 文件，代码如下：
@Autowired
protected JdbcTemplate jdbcTemp;
public List<> getData(String id) {
return jdbcTemp.query("SELECT ........,new RowMapper());
}
But getting java.lang.NullPointerException:
但是得到 java.lang.NullPointerException：
回答by Fernando Aspiazu
If you're using Spring Boot, you can leverage application.propertiesfile by declaring some entries:
如果您使用的是 Spring Boot，则可以application.properties通过声明一些条目来利用文件：
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
In this way there is no need to implement a @Configurationclass to setup database connection in Spring Boot.
这样就不需要@Configuration在 Spring Boot 中实现一个类来设置数据库连接。
You can deepen more here: https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-sql.html
你可以在这里更深入：https: //docs.spring.io/spring-boot/docs/current/reference/html/boot-features-sql.html
By the way, take a look at spring.io
顺便看看spring.io
回答by David Siro
For the java configuration, using Environmentinstance to obtain the properties seems to be the preferred way, as by default ${..}placeholders are not resolved.
对于 java 配置，使用Environment实例获取属性似乎是首选方式，因为默认情况下${..}不解析占位符。
You may use something like this:
你可以使用这样的东西：
@Autowired
private Environment env;
@Bean
public DataSource getDataSource() {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName(env.getProperty("db.driver");
.....
return dataSource;
}
Reasons from the Spring Jira:
来自Spring Jira 的原因：
- it's inconsistent. @PropertySource is the declarative counterpart to ConfigurableEnvironment#addPropertySource. We do not add a PropertySourcesPlaceholderConfigurer in the latter case, and it would be inconsistent to do so in the former. it will not be what the user intended in every (or even most) cases.
- It is entirely possible, and even recommended that @Configuration class users forego $ {...} property replacement entirely, in favor of Environment#getProperty lookups within @Bean methods. For users following this recommendation, the automatic registration of a PropertySorucesPlaceholderConfigurer would be confusing when noticed, and generally undesirable as it's one more moving part. Yes, it's presence is benign, but not cost-free. a PSPC must visit every bean definition in the container to interrogate PropertyValues, only to do nothing in cases where users are going with the Environment#getProperty approach.
- it is solvable (and already solved) by documentation. Proper use of @PropertySource, PropertySourcesPlaceholderConfigurer and other components is pretty comprehensively documented in the Javadoc for @Configuration already, and reference documentation is soon to follow.
- 这是不一致的。@PropertySource 是 ConfigurableEnvironment#addPropertySource 的声明对应物。在后一种情况下我们不添加 PropertySourcesPlaceholderConfigurer，在前一种情况下这样做会不一致。在每种（甚至大多数）情况下，这都不是用户想要的。
- 完全有可能，甚至建议@Configuration 类用户完全放弃 $ {...} 属性替换，转而使用 @Bean 方法中的 Environment#getProperty 查找。对于遵循此建议的用户，PropertySorucesPlaceholderConfigurer 的自动注册在注意到时会令人困惑，并且通常是不可取的，因为它是另一个移动部分。是的，它的存在是良性的，但不是免费的。PSPC 必须访问容器中的每个 bean 定义以询问 PropertyValues，只有在用户使用 Environment#getProperty 方法的情况下什么都不做。
- 它可以通过文档解决（并且已经解决）。@PropertySource、PropertySourcesPlaceholderConfigurer 和其他组件的正确使用已经在@Configuration 的Javadoc 中进行了相当全面的记录，参考文档很快就会跟进。
回答by Arun K
Me too was getting the error when tried to switch from MySQL to MSSQL. The actual issue was I forgot to put the MSSQL dependency in the service. I used mssql-jdbc
尝试从 MySQL 切换到 MSSQL 时，我也遇到了错误。实际问题是我忘记将 MSSQL 依赖项放在服务中。我使用了 mssql-jdbc
