Using NullAway to Avoid NullPointerExceptions – 使用NullAway来避免NullPointerExceptions

We’ve been undertaking numerous strategies over the years, from Elvis operators to Optional, to help remove NullPointerExceptions from our apps. In this tutorial, we’ll learn about Uber’s contribution to the conversation, NullAway, and how to use it.

多年来，我们一直在采取众多策略，从猫王运营商到Optional，以帮助从我们的应用程序中移除NullPointerExceptions。在本教程中，我们将了解Uber对对话的贡献，NullAway，以及如何使用它。

NullAway is a build tool that helps us to eliminate NullPointerExceptions (NPEs) in our Java code.

NullAway是一个构建工具，可以帮助我们消除Java代码中的NullPointerExceptions（NPEs）。

This tool performs a series of type-based, local checks to ensure that any pointer that gets dereferenced in your code cannot be null. It has low build-time overhead and can be configured to run in every build of your code.

这个工具执行了一系列基于类型的本地检查，以确保在你的代码中被解引用的任何指针不能是null。它的构建时间开销很低，可以被配置为在你的代码的每次构建中运行。

2. Installation

2.安装

Let’s take a look at how to install NullAway and its dependencies. In this example, we’re going to configure NullAway using Gradle.

让我们来看看如何安装NullAway及其依赖项。在这个例子中，我们将使用Gradle来配置NullAway。

NullAway is dependant on Error Prone. Therefore, we will add the errorprone plugin:

NullAway依赖于Error Prone>。因此，我们将添加errorprone插件。

plugins {
  id "net.ltgt.errorprone" version "1.1.1"
}

We’ll also add four dependencies in different scopes: annotationProcessor, compileOnly, errorprone, and errorproneJavac:

我们还将在不同范围内添加四个依赖项。annotationProcessor、compileOnly、errorprone和errorproneJavac。

dependencies {
  annotationProcessor "com.uber.nullaway:nullaway:0.7.9"
  compileOnly "com.google.code.findbugs:jsr305:3.0.2"
  errorprone "com.google.errorprone:error_prone_core:2.3.4"
  errorproneJavac "com.google.errorprone:javac:9+181-r4173-1"
}

Finally, we’ll add the Gradle task that configures how NullAway works during the compilation:

最后，我们将添加Gradle任务，配置NullAway在编译过程中的工作方式。

import net.ltgt.gradle.errorprone.CheckSeverity

tasks.withType(JavaCompile) {
    options.errorprone {
        check("NullAway", CheckSeverity.ERROR)
        option("NullAway:AnnotatedPackages", "com.baeldung")
    }
}

The above task sets NullAway severity to the error level which means we can configure NullAway to stop the build with an error. By default, NullAway will just warn the user at compile time.

上述任务将NullAway的严重性设置为错误级别，这意味着我们可以配置NullAway在出现错误时停止构建。默认情况下，NullAway只是在编译时警告用户。

Additionally, the task sets the package to be checked for null dereferences.

此外，该任务还设置了要检查的包，以防止出现空解。

And that’s it, we’re ready now to use the tool in our Java code.

就这样，我们现在已经准备好在我们的Java代码中使用这个工具了。

Similarly, we can use other build systems, Maven or Bazel, to integrate the tool.

同样，我们可以使用其他构建系统、Maven或Bazel,来集成工具。

Integer getAge(Person person) {
    return person.getAge();
}

Integer yearsToRetirement() {
    Person p = null;
    // ... p never gets set correctly...
    return 65 - getAge(p);
}

error: [NullAway] passing @Nullable parameter 'null' where @NonNull is required
    getAge(p);