move nullaway article

libraries-3/README.md

@@ -14,3 +14,5 @@ Remember, for advanced libraries like [Jackson](/jackson) and [JUnit](/testing-m
 - [Introduction to cache2k](https://www.baeldung.com/java-cache2k)
 - [Introduction to the jcabi-aspects AOP Annotations Library](https://www.baeldung.com/java-jcabi-aspects)
 - [Introduction to Takes](https://www.baeldung.com/java-takes)
+- [Using NullAway to Avoid NullPointerExceptions](https://www.baeldung.com/java-nullaway)
+

libraries-3/pom.xml

@@ -94,6 +94,23 @@
             <artifactId>velocity-engine-core</artifactId>
             <version>${velocity-engine-core.version}</version>
         </dependency>
+          <dependency>
+            <groupId>com.uber.nullaway</groupId>
+            <artifactId>nullaway</artifactId>
+            <version>0.3.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.plexus</groupId>
+            <artifactId>plexus-compiler-javac-errorprone</artifactId>
+            <version>2.8</version>
+        </dependency>
+        <!-- override plexus-compiler-javac-errorprone's dependency on
+             Error Prone with the latest version -->
+        <dependency>
+            <groupId>com.google.errorprone</groupId>
+            <artifactId>error_prone_core</artifactId>
+            <version>2.1.3</version>
+        </dependency>
     </dependencies>
 
     <repositories>
@@ -130,6 +147,45 @@
                     </dependency>
                 </dependencies>
             </plugin>
+               <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.5</version>
+                <configuration>
+                    <compilerId>javac-with-errorprone</compilerId>
+                    <forceJavacCompilerUse>true</forceJavacCompilerUse>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                    <showWarnings>true</showWarnings>
+                    <annotationProcessorPaths>
+                        <path>
+                            <groupId>com.uber.nullaway</groupId>
+                            <artifactId>nullaway</artifactId>
+                            <version>0.3.0</version>
+                        </path>
+                    </annotationProcessorPaths>
+                    <compilerArgs>
+                        <!-- NullAway will warn by default, uncomment the next line to make the build fail -->
+                        <!-- <arg>-Xep:NullAway:ERROR</arg> -->
+                        <arg>-XepExcludedPaths:(.*)/test/.*|(.*)/jcabi/.*</arg>
+                        <arg>-XepOpt:NullAway:AnnotatedPackages=com.baeldung.nullaway</arg>
+                    </compilerArgs>
+                </configuration>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.codehaus.plexus</groupId>
+                        <artifactId>plexus-compiler-javac-errorprone</artifactId>
+                        <version>2.8</version>
+                    </dependency>
+                    <!-- override plexus-compiler-javac-errorprone's dependency on
+                         Error Prone with the latest version -->
+                    <dependency>
+                        <groupId>com.google.errorprone</groupId>
+                        <artifactId>error_prone_core</artifactId>
+                        <version>2.3.4</version>
+                    </dependency>
+                </dependencies>
+            </plugin>
         </plugins>
         <resources>
             <resource>

libraries-3/src/main/java/com/baeldung/nullaway/NullAwayExample.java

@@ -0,0 +1,22 @@
+package com.baeldung.nullaway;
+
+public class NullAwayExample {
+
+    /*
+     * 1- NullAway will warn about yearsToRetirement method
+     * 2- Uncomment @Nullable in printAge and NullAway will warn about this method
+     * 3- Add a standard null check to be NullAway compliant
+     * 4- Build will be SUCCESS
+     */
+
+    static Integer getAge(/*@Nullable*/ Person person) {
+        return person.getAge();
+    }
+
+    Integer yearsToRetirement() {
+        Person p = null;
+        // ... p never gets set correctly...
+        return 65 - getAge(p);
+    }
+
+}

libraries-3/src/main/java/com/baeldung/nullaway/Person.java

@@ -0,0 +1,65 @@
+package com.baeldung.nullaway;
+
+public class Person {
+    int age;
+    String name;
+    String email;
+
+    public Person(int age, String name, String email) {
+        super();
+        this.age = age;
+        this.name = name;
+        this.email = email;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder builder = new StringBuilder();
+        builder.append("Person [age=");
+        builder.append(age);
+        builder.append(", name=");
+        builder.append(name);
+        builder.append(", email=");
+        builder.append(email);
+        builder.append("]");
+        return builder.toString();
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((email == null) ? 0 : email.hashCode());
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        Person other = (Person) obj;
+        if (email == null) {
+            if (other.email != null)
+                return false;
+        } else if (!email.equals(other.email))
+            return false;
+        return true;
+    }
+
+}