我非常喜欢检查器框架，它是类型注释(JSR-308)的实现，用于实现像null检查器这样的缺陷检查器。我并没有尝试其他任何方法进行比较，但我对这个实现感到满意。

我没有加入提供该软件的组织，但我是它的粉丝。

我喜欢这个系统的四个方面:

It has a defect checkers for nullness (@Nullable), but also has ones for immutability and interning (and others). I use the first one (nullness) and I'm trying to get into using the second one (immutability/IGJ). I'm trying out the third one, but I'm not certain about using it long term yet. I'm not convinced of the general usefulness of the other checkers yet, but its nice to know that the framework itself is a system for implementing a variety of additional annotations and checkers. The default setting for nullness checking works well: Non-null except locals (NNEL). Basically this means that by default the checker treats everyhing (instance variables, method parameters, generic types, etc) except local variables as if they have a @NonNull type by default. Per the documentation: The NNEL default leads to the smallest number of explicit annotations in your code. You can set a different default for a class or for a method if NNEL doesn't work for you. This framework allows you to use with without creating a dependency on the framework by enclosing your annotations in a comment: e.g. /*@Nullable*/. This is nice because you can annotate and check a library or shared code, but still be able to use that library/shared coded in another project that doesn't use the framework. This is a nice feature. I've grown accustom to using it, even though I tend to enable the Checker Framework on all my projects now. The framework has a way to annotate APIs you use that aren't already annotated for nullness by using stub files.

在等待上游(Java 8?)整理这些注释时，您还可以定义自己的项目本地@NotNull和@Nullable注释。这在使用Java SE时也很有用，因为默认情况下javax.validation.constraints是不可用的。

import java.lang.annotation.*;

/**
 * Designates that a field, return value, argument, or variable is
 * guaranteed to be non-null.
 */
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.LOCAL_VARIABLE})
@Documented
@Retention(RetentionPolicy.CLASS)
public @interface NotNull {}

/**
 * Designates that a field, return value, argument, or variable may be null.
 */
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.LOCAL_VARIABLE})
@Documented
@Retention(RetentionPolicy.CLASS)
public @interface Nullable {}

不可否认，这主要是为了装饰或未来的目的，因为上面显然没有为这些注释的静态分析增加任何支持。

如果你在做一个大项目，你最好创建自己的@Nullable和/或@NotNull注解。

例如:

@java.lang.annotation.Documented
@java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.CLASS)
@java.lang.annotation.Target({java.lang.annotation.ElementType.FIELD,
                              java.lang.annotation.ElementType.METHOD,    
                              java.lang.annotation.ElementType.PARAMETER,
                              java.lang.annotation.ElementType.LOCAL_VARIABLE})
public @interface Nullable 
{
}

如果您使用了正确的保留策略，那么注释在运行时将不可用。从这个角度来看，它只是一种内在的东西。

尽管这不是一门严格的科学，但我认为使用内部类是最有意义的。

这是一个内在的东西。(没有功能或技术影响) 有很多很多的用法。 像IntelliJ这样的IDE支持自定义的@Nullable/@NotNull注释。 大多数框架也喜欢使用自己的内部版本。

其他问题(见评论):

如何在IntelliJ中配置这个?

点击IntelliJ状态栏右下角的“警官”。在弹出窗口中单击“配置巡检”。下一个……

较新的项目可能应该使用jakarta。annotation-api(雅加达。注释包)。 它从现在的只读javax链接。注释回购和适应新的Jakarta生态系统，旨在将社区从所有与javax相关的头痛中解放出来。

Another option is the annotations provided with ANTLR 4. Following Pull Request #434, the artifact containing the @NotNull and @Nullable annotations includes an annotation processor that produces compile-time errors and/or warnings in the event one of these attributes is misused (for example, if both are applied to the same item, or if @Nullable is applied to item with a primitive type). The annotation processor provides additional assurance during the software development process that the information conveyed by the application of these annotations is accurate, including in cases of method inheritance.

如果你正在使用Spring框架构建应用程序，我建议使用来自bean Validation的javax.validation.constraints.NotNull，它被打包在以下依赖项中:

    <dependency>
        <groupId>javax.validation</groupId>
        <artifactId>validation-api</artifactId>
        <version>1.1.0.Final</version>
    </dependency>

这种注释的主要优点是Spring同时支持用javax.validation.constraints.NotNull注释的方法参数和类字段。要启用支持，您需要做的是:

supply the api jar for beans validation and jar with implementation of validator of jsr-303/jsr-349 annotations (which comes with Hibernate Validator 5.x dependency): <dependency> <groupId>javax.validation</groupId> <artifactId>validation-api</artifactId> <version>1.1.0.Final</version> </dependency> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-validator</artifactId> <version>5.4.1.Final</version> </dependency> provide MethodValidationPostProcessor to spring's context @Configuration @ValidationConfig public class ValidationConfig implements MyService { @Bean public MethodValidationPostProcessor providePostProcessor() { return new MethodValidationPostProcessor() } } finally you annotate your classes with Spring's org.springframework.validation.annotation.Validated and validation will be automatically handled by Spring.

例子:

@Service
@Validated
public class MyServiceImpl implements MyService {

  @Override
  public Something doSomething(@NotNull String myParameter) {
        // No need to do something like assert myParameter != null  
  }
}

当您尝试调用方法doSomething并传递null作为参数值时，spring(通过HibernateValidator)将抛出ConstraintViolationException。这里不需要手工工作。

您还可以验证返回值。

javax.validation.constraints.NotNull对Beans验证框架的另一个重要好处是，目前它仍在开发中，新特性计划在新版本2.0中实现。

@Nullable呢?在Beans Validation 1.1中没有类似的东西。好吧，我可以争辩说，如果你决定使用@ nonull，而不是任何没有用@NonNull注释的东西都是有效的“nullable”，所以@Nullable注释是无用的。