我希望使我的代码更具可读性,以及使用工具,如IDE代码检查和/或静态代码分析(FindBugs和Sonar),以避免nullpointerexception。许多工具似乎与彼此的@NotNull/@NonNull/ @NonNull注释不兼容,在我的代码中列出所有这些工具会让人难以阅读。有没有什么建议,哪一个是“最好的”?下面是我找到的等价注释列表:
javax.validation.constraints.NotNull
Created for runtime validation, not static analysis.
documentation
edu.umd.cs.findbugs.annotations.NonNull
Used by FindBugs (dead project) and its successor SpotBugs static analysis and therefore Sonar (now Sonarqube)
FindBugs documentation, SpotBugs documentation
javax.annotation.Nonnull
This might work with FindBugs too, but JSR-305 is inactive. (See also: What is the status of JSR 305?)
source
org.jetbrains.annotations.NotNull
Used by IntelliJ IDEA IDE for static analysis.
documentation
lombok.NonNull
Used to control code generation in Project Lombok.
Placeholder annotation since there is no standard.
source,
documentation
androidx.annotation.NonNull
Marker annotation available in Android, provided by annotation package
documentation
org.eclipse.jdt.annotation.NonNull
Used by Eclipse for static code analysis
documentation
这里已经有太多答案了,但是(a)现在是2019年,仍然没有“标准”Nullable, (b)没有其他答案引用Kotlin。
引用Kotlin是很重要的,因为Kotlin与Java是100%可互操作的,并且它有一个核心的Null安全特性。在调用Java库时,它可以利用这些注释让Kotlin工具知道Java API是否可以接受或返回null。
据我所知,唯一与Kotlin兼容的Nullable包是org.jetbrains.annotations和android.support.annotation(现在是androidx.annotation)。后者只与Android兼容,所以不能在非Android的JVM/Java/Kotlin项目中使用。然而,JetBrains包在任何地方都可以工作。
因此,如果您开发的Java包也应该在Android和Kotlin上工作(并且得到Android Studio和IntelliJ的支持),那么最好的选择可能是JetBrains包。
Maven:
<dependency>
<groupId>org.jetbrains</groupId>
<artifactId>annotations-java5</artifactId>
<version>15.0</version>
</dependency>
Gradle:
implementation 'org.jetbrains:annotations-java5:15.0'
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。