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Bael 1490 the checker framework and java pluggable type systems (#3584) 

* BAEL-1490 First examples, Maven setup

* BAEL-1490 Each checker has its own source file

* BAEL-1490 Added checker for String.format

* BAEL-1490 The Checker Framework and Java Pluggable Type Systems

* Added comments, removed example that is probably too technical for a brad audience.
This commit is contained in:
Daniele Demichelis 2018-02-21 00:00:47 +01:00 committed by pauljervis
parent a72246af2f
commit b35b913cbe
7 changed files with 283 additions and 0 deletions
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114
checker-plugin/pom.xml Normal file
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<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.baeldung</groupId>
<artifactId>checker-plugin</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>checker-plugin</name>
<url>http://maven.apache.org</url>
<!-- https://checkerframework.org/manual/#maven -->
<properties>
<!-- These properties will be set by the Maven Dependency plugin -->
<annotatedJdk>${org.checkerframework:jdk8:jar}</annotatedJdk>
<!-- Uncomment to use the Type Annotations compiler. -->
<!--
<typeAnnotationsJavac>${org.checkerframework:compiler:jar}</typeAnnotationsJavac>
-->
</properties>
<dependencies>
<!-- Annotations from the Checker Framework: nullness, interning, locking, ... -->
<dependency>
<groupId>org.checkerframework</groupId>
<artifactId>checker-qual</artifactId>
<version>2.3.1</version>
</dependency>
<dependency>
<groupId>org.checkerframework</groupId>
<artifactId>checker</artifactId>
<version>2.3.1</version>
</dependency>
<dependency>
<groupId>org.checkerframework</groupId>
<artifactId>jdk8</artifactId>
<version>2.3.1</version>
</dependency>
<!-- The Type Annotations compiler. Uncomment if using annotations in comments. -->
<dependency>
<groupId>org.checkerframework</groupId>
<artifactId>compiler</artifactId>
<version>2.3.1</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<!-- This plugin will set properties values using dependency information -->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
<execution>
<goals>
<!--
Goal that sets a property pointing to the artifact file for each project dependency.
For each dependency (direct and transitive) a project property will be set which
follows the:
groupId:artifactId:type:[classifier]
form and contains the path to the resolved artifact. -->
<goal>properties</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
<!-- Uncomment the following line to use the type annotations compiler. -->
<!-- <fork>true</fork> -->
<compilerArguments>
<Xmaxerrs>10000</Xmaxerrs>
<Xmaxwarns>10000</Xmaxwarns>
</compilerArguments>
<annotationProcessors>
<!-- Add all the checkers you want to enable here -->
<annotationProcessor>org.checkerframework.checker.nullness.NullnessChecker</annotationProcessor>
<annotationProcessor>org.checkerframework.checker.interning.InterningChecker</annotationProcessor>
<annotationProcessor>org.checkerframework.checker.fenum.FenumChecker</annotationProcessor>
<annotationProcessor>org.checkerframework.checker.formatter.FormatterChecker</annotationProcessor>
<annotationProcessor>org.checkerframework.checker.regex.RegexChecker</annotationProcessor>
</annotationProcessors>
<compilerArgs>
<arg>-AprintErrorStack</arg>
<!-- location of the annotated JDK, which comes from a Maven dependency -->
<arg>-Xbootclasspath/p:${annotatedJdk}</arg>
<!--
-->
<!-- Uncomment the following line to use the type annotations compiler. -->
<!--
<arg>-J-Xbootclasspath/p:${typeAnnotationsJavac}</arg>
-->
<!-- Uncomment the following line to turn type-checking warnings into errors. -->
<arg>-Awarns</arg>
</compilerArgs>
</configuration>
</plugin>
</plugins>
</build>
</project>

42
checker-plugin/src/main/java/com/baeldung/typechecker/FakeNumExample.java Normal file
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package com.baeldung.typechecker;
import org.checkerframework.checker.fenum.qual.Fenum;
//@SuppressWarnings("fenum:assignment.type.incompatible")
public class FakeNumExample {
// Here we use some String constants to represents countries.
static final @Fenum("country") String ITALY = "IT";
static final @Fenum("country") String US = "US";
static final @Fenum("country") String UNITED_KINGDOM = "UK";
// Here we use other String constants to represent planets instead.
static final @Fenum("planet") String MARS = "Mars";
static final @Fenum("planet") String EARTH = "Earth";
static final @Fenum("planet") String VENUS = "Venus";
// Now we write this method and we want to be sure that
// the String parameter has a value of a country, not that is just a String.
void greetCountries(@Fenum("country") String country) {
System.out.println("Hello " + country);
}
// Similarly we're enforcing here that the provided
// parameter is a String that represent a planet.
void greetPlanets(@Fenum("planet") String planet) {
System.out.println("Hello " + planet);
}
public static void main(String[] args) {
FakeNumExample obj = new FakeNumExample();
// This will fail because we pass a planet-String to a method that
// accept a country-String.
obj.greetCountries(MARS);
// Here the opposite happens.
obj.greetPlanets(US);
}
}

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checker-plugin/src/main/java/com/baeldung/typechecker/FormatExample.java Normal file
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package com.baeldung.typechecker;
public class FormatExample {
public static void main(String[] args) {
// Just enabling org.checkerframework.checker.formatter.FormatterChecker
// we can be sure at compile time that the format strings we pass to format()
// are correct. Normally we would have those errors raised just at runtime.
// All those formats are in fact wrong.
String.format("%y", 7); // error: invalid format string
String.format("%d", "a string"); // error: invalid argument type for %d
String.format("%d %s", 7); // error: missing argument for %s
String.format("%d", 7, 3); // warning: unused argument 3
String.format("{0}", 7); // warning: unused argument 7, because {0} is wrong syntax
}
}

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checker-plugin/src/main/java/com/baeldung/typechecker/KeyForExample.java Normal file
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package com.baeldung.typechecker;
import org.checkerframework.checker.nullness.qual.KeyFor;
import java.util.HashMap;
import java.util.Map;
public class KeyForExample {
private final Map<String, String> config = new HashMap<>();
KeyForExample() {
// Here we initialize a map to store
// some config data.
config.put("url", "http://1.2.3.4");
config.put("name", "foobaz");
}
public void dumpPort() {
// Here, we want to dump the port value stored in the
// config, so we declare that this key has to be
// present in the config map.
// Obviously that will fail because such key is not present
// in the map.
@KeyFor("config") String key = "port";
System.out.println( config.get(key) );
}
}

28
checker-plugin/src/main/java/com/baeldung/typechecker/MonotonicNotNullExample.java Normal file
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package com.baeldung.typechecker;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import java.util.Date;
public class MonotonicNotNullExample {
// The idea is we need this field to be to lazily initialized,
// so it starts as null but once it becomes not null
// it cannot return null.
// In these cases, we can use @MonotonicNonNull
@MonotonicNonNull private Date firstCall;
public Date getFirstCall() {
if (firstCall == null) {
firstCall = new Date();
}
return firstCall;
}
public void reset() {
// This is reported as error because
// we wrongly set the field back to null.
firstCall = null;
}
}

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checker-plugin/src/main/java/com/baeldung/typechecker/NonNullExample.java Normal file
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package com.baeldung.typechecker;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;
public class NonNullExample {
// This method's parameter is annotated in order
// to tell the pluggable type system that it can never be null.
private static int countArgs(@NonNull String[] args) {
return args.length;
}
// This method's parameter is annotated in order
// to tell the pluggable type system that it may be null.
public static void main(@Nullable String[] args) {
// Here lies a potential error,
// because we pass a potential null reference to a method
// that does not accept nulls.
// The Checker Framework will spot this problem at compile time
// instead of runtime.
System.out.println(countArgs(args));
}
}

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checker-plugin/src/main/java/com/baeldung/typechecker/RegexExample.java Normal file
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package com.baeldung.typechecker;
import org.checkerframework.checker.regex.qual.Regex;
public class RegexExample {
// For some reason we want to be sure that this regex
// contains at least one capturing group.
// However, we do an error and we forgot to define such
// capturing group in it.
@Regex(1) private static String findNumbers = "\\d*";
public static void main(String[] args) {
String message = "My phone number is +3911223344.";
message.matches(findNumbers);
}
}