Question

我有一个myapp.properties文件，其键值对定义为：

prefix.int-field=123
prefix.string-field=asdf
prefix.custom-type-field=my.package.CustomType

我试图通过在以下类中使用@Value注释来注入这些属性：

@PropertySource(value = "classpath:myapp.properties")
@Component
class MySettings {
    @Value("${prefix.int-field}")
    private int intField;

    @Value("${prefix.string-field}")
    private String stringField;

    @Value("${prefix.custom-type-field}") // <-- this is the problem
    private CustomInterface customField;
}

class CustomType implements CustomInterface {...}

interface CustomInterface {...}

现在，intField和stringField按预期使用所需的值进行初始化，但customField会引发异常：

Caused by: java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [my.package.CustomInterface]: no matching editors or conversion strategy found
    at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:303) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
    at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:125) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
    at org.springframework.beans.TypeConverterSupport.doConvert(TypeConverterSupport.java:61) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]

如何将文本属性值转换为自定义类型？

我试图咨询documentation，但我没有看到正确的方法。我使用的是Spring Boot 1.3.6。

Answer 1

要解决您的直接问题，您需要查看bean上的@PostConstruct选项。这将允许您在bean可用于上下文之前对事物采取行动。

@PropertySource(value = "classpath:myapp.properties")
@Component
class MySettings {
    @Value("${prefix.int-field}")
    private int intField;

    @Value("${prefix.string-field}")
    private String stringField;

    @Value("${prefix.custom-type-field}")
    private String customFieldType;

    private CustomInterface customField;

    @PostConstruct
    public void init() {
        customField = (CustomInterface) Class.forName(customFieldType).newInstance(); // short form... will need checks that it finds the class and can create a new instance
    }
}

class CustomType implements CustomInterface {...}

interface CustomInterface {...}

我很好奇你是否想在类上使用@Configuration注释并创建一个在Spring ApplicationContext上作为bean提供的CustomInterface实例。要做到这一点，你会做这样的事情：

@Component
@ConfigurationProperties(prefix = "prefix")
class MySettings {
    private int intField;

    private String stringField;

    private String customTypeField;

    // getters and setters
}

然后将在@Configuration类中使用：

@Configuration
class MyConfiguration {
    @Bean
    public CustomInterface customInterface(MySettings mySettings) {
        return (CustomInterface) Class.forName(mySettings.getCustomTypeField()).newInstance();
    }
}

此时您将拥有CustomInterface的实例化bean，您可以将Spring自动装配到其他对象中。

属性值的自定义类型转换

1 个答案: