Modernizer Maven Plugin detects uses of legacy APIs which modern Java versions supersede. These modern APIs are often more performant, safer, and idiomatic than the legacy equivalents. For example, Modernizer can detect uses of Vector instead of ArrayList, String.getBytes(String) instead of String.getBytes(Charset), and Guava Objects.equal instead of Java 7 Objects.equals. The default configuration detects over 200 legacy APIs, including third-party libraries like Apache Commons, Guava, and Joda-Time.

To run Modernizer, add the following to the <plugins> stanza in your pom.xml then invoke mvn modernizer:modernizer:

<plugin>
  <groupId>org.gaul</groupId>
  <artifactId>modernizer-maven-plugin</artifactId>
  <version>2.7.0</version>
  <configuration>
    <javaVersion>8</javaVersion>
  </configuration>
</plugin>

The <configuration> stanza can contain several elements:

• <javaVersion> enables violations based on target Java version, e.g., 8. For example, Modernizer will detect uses of Vector as violations when targeting Java 1.2 but not when targeting Java 1.1. Required parameter.
• <failOnViolations> fail phase if Modernizer detects any violations. Defaults to true.
• <includeTestClasses> run Modernizer on test classes. Defaults to true.
• <violationsFile> user-specified violation file. Also disables standard violation checks. Can point to classpath using absolute paths, e.g. classpath:/your/file.xml.
• <violationsFiles> user-specified violations file. The latter files override violations from the former ones, including violationsFile and the default violations. Can point to classpath using absolute paths, e.g. classpath:/your/file.xml.
• <exclusionsFile> disables user-specified violations. This is a text file with one exclusion per line in the javap format: java/lang/String.getBytes:(Ljava/lang/String;)[B. Empty lines and lines starting with # are ignored.
• <exclusions> violations to disable. Each exclusion should be in the javap format: java/lang/String.getBytes:(Ljava/lang/String;)[B.
• <exclusionPatterns> violation patterns to disable, specified using <exclusionPattern> child elements. Each exclusion should be a regular expression that matches the javap format: java/lang/.* of a violation.
• <ignorePackages> package prefixes to ignore, specified using <ignorePackage> child elements. Specifying foo.bar subsequently ignores foo.bar.*, foo.bar.baz.* and so on.
• <ignoreClassNamePatterns> full qualified class names (incl. package) to ignore, specified using <ignoreClassNamePattern> child elements. Each exclusion should be a regular expression that matches a package and/or class; the package will be / not . separated (ASM's format).
• <ignoreGeneratedClasses> classes annotated with an annotation whose retention policy is runtime or class and whose simple name contain "Generated" will be ignored. (Note: both javax.annotation.Generated and javax.annotation.processing.Generated have retention policy SOURCE (aka discarded by compiler).)

To run Modernizer during the verify phase of your build, add the following to the modernizer <plugin> stanza in your pom.xml:

<executions>
  <execution>
    <id>modernizer</id>
    <phase>verify</phase>
    <goals>
      <goal>modernizer</goal>
    </goals>
  </execution>
</executions>

Command-line flags can override Modernizer configuration and ModernizerMojo documents all of these. The most commonly used flags:

• -Dmodernizer.failOnViolations - fail phase if violations detected, defaults to true
• -Dmodernizer.skip - skip plugin execution, defaults to false

The plugin can output Modernizer violations in one of many formats which can be configured with the <configuration> stanza using <outputFormat>.

The currently supported formats and their respective configuration options are outlined below:

• CONSOLE List each violation using Maven's logger. This is the default format.
  • <violationLogLevel> Specify the log level of the logger: error, warn, info or debug. Default is error.
• CODE_CLIMATE Write the violations according to Code Climate's Spec. GitLab uses this format for its code quality as shown here.
  • <outputFile> The full path the file to output to. Default is ${project.build.directory}/code-quality.json
  • <codeClimateSeverity> Severity of Modernizer violations for CodeClimate: INFO, MINOR, MAJOR, CRITICAL or BLOCKER. Default is MINOR.

Code can suppress violations within a class or method via an annotation. First add the following dependency to your pom.xml:

<dependencies>
  <dependency>
    <groupId>org.gaul</groupId>
    <artifactId>modernizer-maven-annotations</artifactId>
    <version>2.7.0</version>
  </dependency>
</dependencies>

Then add @SuppressModernizer to the element to ignore:

import org.gaul.modernizer_maven_annotations.SuppressModernizer;

public class Example {
    @SuppressModernizer
    public static void method() { ... }
}

• ASM provides Java bytecode introspection which enables Modernizer's checks
• Checkstyle IllegalInstantiation and Regexp checks can mimic some of Modernizer's functionality
• Google Error Prone JdkObsolete can mimic some of Modernizer's functionality
• Gradle Modernizer Plugin provides a Gradle interface to Modernizer
• javac -Xlint:deprecated detects uses of interfaces with @Deprecated annotations
• Overstock.com library-detectors detects uses of interfaces with @Beta annotations
• Policeman's Forbidden API Checker provides similar functionality to Modernizer

Copyright (C) 2014-2022 Andrew Gaul

Licensed under the Apache License, Version 2.0