No NPE!

Feedback and high-quality pull requests are highly welcome!

1. What is it?
2. Usage
   1. Binaries
   2. Building from Sources
   3. Validating/Updating EEA files
   4. Adding a new Maven module
3. Acknowledgement
4. License

What is it?

No NPE! is a repository of Eclipse External Null Annotations for better static Null Analysis with the Eclipse Java Compiler (ecj).

Usage

Usage of External Null Annotations in Eclipse is documented at https://help.eclipse.org/latest/index.jsp?topic=/org.eclipse.jdt.doc.user/tasks/task-using_external_null_annotations.htm

Binaries

Latest Release binaries are available on Maven central, see https://search.maven.org/search?q=g%3Acom.vegardit.no-npe

Latest Snapshot binaries are available via the mvn-snapshots-repo git branch. You need to add this repository configuration to your Maven settings.xml:

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.2.0 https://maven.apache.org/xsd/settings-1.2.0.xsd">
  <profiles>
    <profile>
      <repositories>
        <repository>
          <id>no-npe-snapshots</id>
          <name>no-npe-snapshots</name>
          <url>https://raw.githubusercontent.com/vegardit/no-npe/mvn-snapshots-repo</url>
          <releases><enabled>false</enabled></releases>
          <snapshots><enabled>true</enabled></snapshots>
        </repository>
      </repositories>
    </profile>
  </profiles>
  <activeProfiles>
    <activeProfile>no-npe-snapshots</activeProfile>
  </activeProfiles>
</settings>

Building from Sources

To ensure reproducible builds this Maven project inherits from the vegardit-maven-parent project which declares fixed versions and sensible default settings for all official Maven plug-ins.

The project also uses the maven-toolchains-plugin which decouples the JDK that is used to execute Maven and it's plug-ins from the target JDK that is used for compilation and/or unit testing. This ensures full binary compatibility of the compiled artifacts with the runtime library of the required target JDK.

To build the project follow these steps:

1. Download and install Java 11, Java 17 AND Java 21 SDKs, e.g. from:

   • Java 11: https://adoptium.net/releases.html?variant=openjdk11 or https://www.azul.com/downloads/?version=java-11-lts&package=jdk#download-openjdk
   • Java 17: https://adoptium.net/releases.html?variant=openjdk17 or https://www.azul.com/downloads/?version=java-17-lts&package=jdk#download-openjdk
   • Java 21: https://adoptium.net/releases.html?variant=openjdk21 or https://www.azul.com/downloads/?version=java-21-lts&package=jdk#download-openjdk

2. Download and install the latest Maven distribution.

3. In your user home directory create the file .m2/toolchains.xml with the following content:

   <?xml version="1.0" encoding="UTF8"?>
   <toolchains xmlns="http://maven.apache.org/TOOLCHAINS/1.1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://maven.apache.org/TOOLCHAINS/1.1.0 https://maven.apache.org/xsd/toolchains-1.1.0.xsd">
      <toolchain>
         <type>jdk</type>
         <provides>
            <version>11</version>
            <vendor>default</vendor>
         </provides>
         <configuration>
            <jdkHome>[PATH_TO_YOUR_JDK_11]</jdkHome>
         </configuration>
      </toolchain>
      <toolchain>
         <type>jdk</type>
         <provides>
            <version>17</version>
            <vendor>default</vendor>
         </provides>
         <configuration>
            <jdkHome>[PATH_TO_YOUR_JDK_17]</jdkHome>
         </configuration>
      </toolchain>
      <toolchain>
         <type>jdk</type>
         <provides>
            <version>21</version>
            <vendor>default</vendor>
         </provides>
         <configuration>
            <jdkHome>[PATH_TO_YOUR_JDK_21]</jdkHome>
         </configuration>
      </toolchain>
   </toolchains>

   Set the [PATH_TO_YOUR_JDK_11]/[PATH_TO_YOUR_JDK_17]/[PATH_TO_YOUR_JDK_21] parameters accordingly to where you installed the JDKs.

4. Checkout the code, e.g. using:

   • git clone https://github.com/vegardit/no-npe

5. Run mvn clean verify in the project root directory. This will execute compilation, unit-testing, integration-testing and packaging of all artifacts.

Validating/Updating EEA files

The EEA files can be validated/updated using:

# validate all EEA files of all eea-* modules
mvn compile

# validate all EEA files of a specific module
mvn compile -am -pl <MODULE_NAME>
mvn compile -am -pl libs/eea-commons-io-2

# update/regenerate all EEA files of all eea-* modules
mvn compile -Deea-generator.action=generate

# update/regenerate all EEA files of a specific module
mvn compile -Deea-generator.action=generate -am -pl <MODULE_NAME>
mvn compile -Deea-generator.action=generate -am -pl libs/eea-commons-io-2

Updating EEA files will:

• add new types/fields/methods found
• remove obsolete declarations from the EEA files
• preserve null/non-null annotations specified for existing fields/methods

Adding a new Maven module

1. Create a new sub-directory under libs/ using the name pattern eea-[LIBRARY_NAME]-[LIBRARY_MAJOR_VERSION|latest]

2. Create a pom.xml in the new directory like this:

   <?xml version="1.0"?>
   <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   
     <modelVersion>4.0.0</modelVersion>
   
     <parent>
       <groupId>com.vegardit.no-npe</groupId>
       <artifactId>no-npe-parent</artifactId>
       <version>[CURRENT_SNAPSHOT_VERSION]</version>
     </parent>
   
     <artifactId>no-npe-eea-[LIBRARY_NAME]-[LIBRARY_MAJOR_VERSION]</artifactId>
   
     <dependencies>
       <dependency>
         <groupId>[LIBRARY_GROUP_ID]</groupId>
         <artifactId>[LIBRARY_ARTIFACT_ID]</artifactId>
         <version>[LIBRARY_VERSION]</version>
         <scope>provided</scope>
       </dependency>
     </dependencies>
   </project>

   For example:

   <?xml version="1.0"?>
   <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   
     <modelVersion>4.0.0</modelVersion>
   
     <parent>
       <groupId>com.vegardit.no-npe</groupId>
       <artifactId>no-npe-parent</artifactId>
       <version>1.0.0-SNAPSHOT</version>
     </parent>
   
     <artifactId>no-npe-eea-cool-library4</artifactId>
   
     <dependencies>
       <dependency>
         <groupId>org.example.cool-library</groupId>
         <artifactId>cool-library</artifactId>
         <version>2.0.2</version>
         <scope>provided</scope>
       </dependency>
     </dependencies>
   </project>

3. Add an eea-generator.properties file in the same directory where you specify the relevant packages of the library.

   packages.include=package1,package2

   E.g.

   packages.include=org.example.cool-library.api,org.example.cool-library.spi

   The following options are available:

   name	description	default
   packages.include	The comma separated packages to recursively scan for class files	n/a
   classes.exclude	A comma separated list of regex patterns that are matched against fully qualified class names to exclude them from scanning	n/a
   action	The default action (validate or generate to perform during mvn compile)	validate
   output.dir	Path to the root directory containing the .eea files. Used for validation and generation.	src/main/resources
   input.dirs	Comma separated additional paths of root directories containing .eea files to read null annotations from on generate.	n/a
   omitRedundantAnnotatedSignatures	If true lines with annotated signatures are not written to the file if they don't contain any null annotations	false

   These options can also be specified in the command line as system properties like -Deea-generator.<OPTION_NAME>=, e.g. -Deea-generator.omitRedundantAnnotatedSignatures=true

4. In the parent project's pom.xml file reference the module in the <modules> section.

5. Run the generator in the parent project to create the EEA files

   mvn compile -Deea-generator.action=generate -am -pl <MODULE_NAME>

   E.g.

   mvn compile -Deea-generator.action=generate -am -pl libs/eea-cool-library-2

6. Manually add missing null/non-null annotations in the generated EEA files under src/main/resources

Acknowledgement

No NPE! was created by Sebastian Thomschke and is sponsored by Vegard IT GmbH.

Creation of this project was inspired by https://github.com/lastnpe/eclipse-null-eea-augments/ but a different approach in generating/packaging/validating of EEA files/archives has been taken.

No NPE! would not have been possible in its current form without the following technologies and learning resources:

Technologies/Libraries

• ClassGraph - fast Java classpath scanner
• gmavenplus-plugin - Maven plugin to execute arbitrary Groovy code during Maven lifecycle phases
• exec-maven-plugin - toolchain aware Maven plugin to execute custom Java code during Maven lifecycle phases
• AssertJ - strongly-typed assertions for unit testing

Tutorials

• Null Analysis/External Annotations https://wiki.eclipse.org/JDT_Core/Null_Analysis/External_Annotations
• Using external null annotations https://help.eclipse.org/latest/index.jsp?topic=/org.eclipse.jdt.doc.user/tasks/task-using_external_null_annotations.htm
• Type Signature Syntax https://help.eclipse.org/latest/index.jsp?topic=/org.eclipse.jdt.doc.isv/reference/api/org/eclipse/jdt/core/Signature.html
• NullPointerException presentation given at EclipseCon Europe 2016 https://www.slideshare.net/mikervorburger/the-end-of-the-world-as-we-know-it-aka-your-last-nullpointerexception-1b-bugs
• Field Descriptors https://docs.oracle.com/javase/specs/jvms/se11/html/jvms-4.html#jvms-4.3.2

License

All files are released under the Eclipse Public License 2.0.

Individual files contain the following tag instead of the full license text:

SPDX-License-Identifier: EPL-2.0

This enables machine processing of license information based on the SPDX License Identifiers that are available here: https://spdx.org/licenses/.