# 3.2. 将代码解析为错误消息

我们涵盖了数据绑定和验证。本节介绍与验证错误相对应的输出消息。在上[一节](https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#validator)所示的示例中，我们拒绝了`name`和`age`字段。如果我们想通过使用`MessageSource`来输出错误消息 ，我们可以使用我们在拒绝字段时提供的错误代码（在本例中为“姓名”和“年龄”）来完成。当您调用（直接或间接，通过使用例如`ValidationUtils`类）`rejectValue`或`Errors`接口中的其他`reject`方法之一时，底层实现不仅注册您传入的代码，而且还注册许多额外的错误代码。`MessageCodesResolver` 确定`Errors`接口寄存器的错误代码。默认情况下， 使用`DefaultMessageCodesResolver`，它（例如）不仅使用您提供的代码注册消息，而且还注册包含您传递给拒绝方法的字段名称的消息。所以，如果你用`rejectValue("age", "too.darn.old")` 拒绝一个字段，除了代码`too.darn.old`之外，Spring 还会注册`too.darn.old.age`和 `too.darn.old.age.int`（第一个包含字段名称，第二个包含字段类型）。这样做是为了方便开发人员定位错误消息。

有关`MessageCodesResolver`和 默认策略的更多信息可以分别在[`MessageCodesResolver`](https://docs.spring.io/spring-framework/docs/5.3.22/javadoc-api/org/springframework/validation/MessageCodesResolver.html)和 [`DefaultMessageCodesResolver`](https://docs.spring.io/spring-framework/docs/5.3.22/javadoc-api/org/springframework/validation/DefaultMessageCodesResolver.html)的 javadoc 中找到 。


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