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    <p>You can apply <code>@CheckForNull</code> to all method return values (and/or parameters) within a package by adding the annotation to the package's <code>package-info.java</code> file, but you won't have control over individual methods.</p> <p>First, create <code>@ReturnValuesAreCheckForNullByDefault</code> in a utility package of your project.</p> <pre><code>@Documented @CheckForNull @TypeQualifierDefault(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface ReturnValuesAreCheckForNullByDefault { /* noop */ } </code></pre> <p>Next, create <code>src/java/util/package-info.java</code>.</p> <pre><code>@ReturnValuesAreCheckForNullByDefault package java.util; import my.project.util.ReturnValuesAreCheckForNullByDefault; </code></pre> <p>Finally, enjoy your FindBugs warnings.</p> <pre><code>@Nonnull public String getValue() { Map&lt;String, String&gt; values = new HashMap&lt;&gt;(); return values.get("foo"); // &lt;-- Possible null pointer dereference ... } </code></pre> <p>The problem with doing this is that there are many methods in the <code>java.*</code> packages that contractually <em>do not</em> return <code>null</code>. Using these without checking for <code>null</code> will raise warnings. For example, this NPE-safe code also raises a warning:</p> <pre><code>@Nonnull public Set&lt;String&gt; getNotNull() { Map&lt;String, String&gt; values = new HashMap&lt;&gt;(); return values.keySet(); } </code></pre> <p>You can suppress the warning with <code>@SuppressFBWarnings</code>, but this may clutter up the code too much for your liking.</p>
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    1. POHow to use findbugs @Nonnull with external libraries?
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    1. USDavid Harkness
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    1. POHow to use findbugs @Nonnull with external libraries?
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    1. COHow does Findbugs know about `@ReturnValuesAreCheckForNullByDefault`? I mean, how does FB know how to interpret your custom annotation?
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      1. USThomas Jensen
    2. CO[`TypeQualifierDefault`](http://jsr-305.googlecode.com/svn/trunk/javadoc/javax/annotation/meta/TypeQualifierDefault.html) is part of JSR-305 and causes the other annotations to be carried over to the elements (methods, parameters, fields, etc. depending on its parameter) annotated with the annotation to which it is attached. See [`ParametersAreNonnullByDefault`](http://jsr-305.googlecode.com/svn/trunk/javadoc/javax/annotation/ParametersAreNonnullByDefault.html) for an example from JSR-305, nearly identical to the above.
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      1. USDavid Harkness
    3. COThanks, I knew the package-info.java, but didn't think of writing one for a package outside of my control. However, I think you're right, that not being able to make certain Util-methods @Nonnull will be quite annoying.
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      1. USThomas M.
 

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