Jackdaw is a Java Annotation Processor which allows to simplify Java/Android development and prevents writing of tedious code.

Jackdaw was inspired by Lombok project, but in comparison with Lombok:

• it does not need to have an extra plugin in IDE
• it does not modify the existing source code

Jackdaw supports the following compile time annotations:

• @JAdapter
• @JBean
• @JBuilder
• @JClassDescriptor
• @JComparator
• @JFactoryMethod
• @JFunction
• @JMessage
• @JPredicate
• @JRepeatable
• @JService

Jackdaw uses JitPack.io for distribution, so you need to configure JitPack's Maven repository to fetch artifacts (dependencies).

It is necessary to make dependency on jackdaw-core. This module contains compile time annotations which will be used to give a hints for APT.

Example configuration for Maven:

<repository>
    <id>jitpack.io</id>
    <url>https://jitpack.io</url>
</repository>

<dependencies>
    <dependency>
        <groupId>com.github.vbauer</groupId>
        <artifactId>jackdaw.jackdaw-core</artifactId>
        <version>${jackdaw.version}</version>
    </dependency>
</dependencies>

After that, you need to configure maven-compiler-plugin:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>${maven.compiler.plugin.version}</version>
            <configuration>
                <forceJavacCompilerUse>true</forceJavacCompilerUse>
            </configuration>
            <dependencies>
                <dependency>
                    <groupId>com.github.vbauer</groupId>
                    <artifactId>jackdaw.jackdaw-apt</artifactId>
                    <version>${jackdaw.version}</version>
                </dependency>
            </dependencies>
        </plugin>
    </plugins>
</build>

Available parameters for annotation processor:

• addSuppressWarningsAnnotation - Add @SuppressWarnings("all") annotation on all generated classes to prevent unnecessary issues of IDE inspections (default value is true).
• addGeneratedAnnotation - Add @Generated annotation on all generated classes to have possibility skip execution of static code analysis (default value is true).
• addGeneratedDate - Add date parameter to @Generated annotation. It is also necessary to switch on addGeneratedAnnotation parameter (default value is false).

Example configuration for maven-compiler-plugin:

<configuration>
    <compilerArgs>
        <arg>-AaddGeneratedAnnotation=true</arg>
        <arg>-AaddGeneratedDate=true</arg>
        <arg>-AaddSuppressWarningsAnnotation=false</arg>
    </compilerArgs>
</configuration>

Some things that you need to know before exploring an examples:

• Code style in the below examples was changed to minimize text in README.
• Some annotations and imports were also removed to simplify understanding.
• All generated classes will have the same package as original classes.

@JAdapter allows to create class with empty method implementations using some interface or class. Using generated class, you can override only needed methods (like in Swing, ex: MouseAdapter).

Original class MouseListener:

@JAdapter
public interface MouseListener {
    void onMove(int x, int y);
    void onPressed(int button);
}

Generated class MouseListenerAdapter:

public class MouseListenerAdapter implements MouseListener {
    public void onMove(final int x, final int y) {
    }
    public void onPresses(final int button) {
    }
}

@JBean generates some boilerplate code that is normally associated with simple POJOs (Plain Old Java Objects) and beans:

• getters for all non-static/private fields,
• setters for all non-static/private/final fields,
• and copy constructors from super class

Original class AbstractUserModel:

@JBean
public abstract class AbstractUserModel {
    protected int id;
    protected String username;
    protected String password;
    protected boolean admin;
}

Generated class User:

public class User extends AbstractUserModel {
    public User() { super(); }

    public void setId(final int id) { this.id = id; }
    public void getId() { return id; }
    
    public String getUsername() { return username; }
    public void setUsername(final String username) { this.username = username; }
    
    public String getPassword() { return password; }
    public void setPassword(final String password) { this.password = password; }
    
    public boolean isAdmin() { return admin; }
    public void setAdmin(final boolean admin) { this.admin = admin; }
}

Prefix 'Abstract' and postfix 'Model' will be removed if they are presented.

The @JBuilder annotation produces complex builder APIs for your classes.

Original class Company:

@JBuilder
public class Company {
    private int id;
    private String name;
    private Set<String> descriptions;

    public int getId() { return id; }
    public void setId(final int id) { this.id = id; }

    public String getName() { return name; }
    public void setName(final String name) { this.name = name; }

    public Set<String> getDescriptions() { return descriptions; }
    public void setDescriptions(final Set<String> descriptions) { this.descriptions = descriptions; }
}

Generated class CompanyBuilder:

public class CompanyBuilder {
    private int id;
    private String name;
    private Set<String> descriptions;

    public static CompanyBuilder create() {
        return new CompanyBuilder();
    }
    public CompanyBuilder id(final int id) {
        this.id = id;
        return this;
    }
    public CompanyBuilder name(final String name) {
        this.name = name;
        return this;
    }
    public CompanyBuilder descriptions(final Set<String> descriptions) {
        this.descriptions = descriptions;
        return this;
    }
    public Company build() {
        final Company object = new Company();
        object.setId(id);
        object.setName(name);
        object.setListed(listed);
        object.setDescriptions(descriptions);
        return object;
    }
}

@JBuilder lets you automatically produce the code required to have your class be instantiable with code such as:

CompanyBuilder.create()
    .id(1)
    .name("John Smith")
    .descriptions(Collections.singleton("Good guy"))
    .build()

Sometimes it is necessary to use reflection, so it will be useful to have some string constants. @JClassDescriptor generates it for you easily.

Available parameters:

• fields - generate information about fields (default is true).
• methods - generate information about methods (default is true).

Original class Company:

@JClassDescriptor
public class Company {
    private int id;
    private String name;

    public int getId() { return id; }
    public void setId(final int id) { this.id = id; }

    public String getName() { return name; }
    public void setName(final String name) { this.name = name; }
}

Generated class CompanyClassDescriptor:

public final class CompanyClassDescriptor {
    public static final String FIELD_ID = "id";
    public static final String FIELD_NAME = "name";

    public static final String METHOD_ID = "getId";
    public static final String METHOD_SET_ID = "setId";
    public static final String METHOD_NAME = "getName";
    public static final String METHOD_SET_NAME = "setName";

    private CompanyClassDescriptor() {
        throw new UnsupportedOperationException();
    }
}

To generated safe and well-coded comparator, you have to write a lot of boilerplate code. @JComparator annotation allows to simplify this situation. To generate reverse order comparator, use parameter reverse.

There are several ways to generate comparator or group of comparators. It depends on the annotation location:

• annotation on field - generate comparator only for one specified field.
• annotation on method without args - generate comparator using method with empty list of arguments and non-void return-value.
• annotation on class - generate comparators using 2 previous strategies (for all fields and simple methods).

Original class Company:

public class Company {
    @JComparator private String name;
    private long revenue;
    
    public String getName() { return name; }
    public void setName(final String name) { this.name = name; }

    @JComparator public long getRevenue() { return revenue; }
    public void setRevenue(final long revenue) { this.revenue = revenue; }
}

Generated class CompanyComparators:

public final class CompanyComparators {
    public static final Comparator<Company> NAME = new Comparator<Company>() {
        public int compare(final Company o1, final Company o2) {
            final String v1 = o1 == null ? null : o1.getName();
            final String v2 = o2 == null ? null : o2.getName();
            if (v1 == v2) {
                return 0;
            } else if (v1 == null) {
                return -1;
            } else if (v2 == null) {
                return 1;
            }
            return v1.compareTo(v2);
        }
    };
    public static final Comparator<Company> REVENUE = new Comparator<Company>() {
        public int compare(final Company o1, final Company o2) {
            final Long v1 = o1 == null ? null : o1.getRevenue();
            final Long v2 = o2 == null ? null : o2.getRevenue();
            if (v1 == v2) {
                return 0;
            } else if (v1 == null) {
                return -1;
            } else if (v2 == null) {
                return 1;
            }
            return v1.compareTo(v2);
        }
    };
    private CompanyComparators() {
        throw new UnsupportedOperationException();
    }
}

@JFactoryMethod allows to use pattern Factory Method for object instantiation. To use this annotation it is necessary to have setters and default constructor in original class.

Available parameters:

• method - factory method name (default value is "create").
• all - use all fields of class in factory method (default value is true).
• arguments - use only specified fields in factory method (it is an empty array by default).

Original class Company:

@JFactoryMethod
public class Company {
    private int id;
    private String name;

    public int getId() { return id; }
    public void setId(final int id) { this.id = id; }

    public String getName() { return name; }
    public void setName(final String name) { this.name = name; }
}

Generated class CompanyFactory:

public final class CompanyFactory {
    private CompanyFactory() {
        throw new UnsupportedOperationException();
    }
    public static Company create(final int id, final String name) {
        final Company object = new Company();
        object.setId(id);
        object.setName(name);
        return object;
    }
}

The @JFunction annotation generates Function implementation to use functional-way for programming. You can specify different function interfaces for implementation generation (JFunctionType):

• GUAVA - Guava functions (com.google.common.base.Function)
• JAVA - functions from Java 8 (java.util.function.Function)

There are several ways to generate function or group of functions. It depends on the annotation location:

• annotation on field - generate function only for one specified field.
• annotation on method without args - generate function using method with empty list of arguments and non-void return-value.
• annotation on class - generate functions using 2 previous strategies (for all fields and simple methods).

Original class Company:

public class Company {
    @JFunction private int id;
    
    public int getId() { return id; }
    public void setId(final int id) { this.id = id; }
}

Generated class CompanyFunctions:

public final class CompanyFunctions {
    public static final Function<Company, Integer> ID = new Function<Company, Integer>() {
        public Integer apply(final Company input) {
            return (input != null) ? input.getId() : null;
        }
    };
}

The @JMessage annotation does not generate any additional code, instead of this it prints information in logs during project compiling. It could be useful to make some really meaningful notes for you or your team, instead of using TODOs in comments.

Available parameters:

• value - List of notes, that will be logged.
• type - Logging level (default value is Diagnostic.Kind.MANDATORY_WARNING).
• details - Add information about annotated element with note message (default value is false).
• showAfter - Show message only after the given date. It could be useful to specify deadline. Supported formats:
  • yyyy-MM-dd
  • yyyy/MM/dd
  • dd-MM-yyyy
  • dd/MM/yyyy

Example:

@JMessage({
    "Do not forget to remove this class in the next release",
    "MouseListener interface will be used instead of it"
})
public abstract class AbstractMouseListener implements MouseListener {
    // Some piece of code.
}

Part of compilation output:

[INFO] --- maven-processor-plugin:2.2.4:process (process) @ jackdaw-sample ---
[WARNING] diagnostic: warning: Do not forget to remove this class in the next release
[WARNING] diagnostic: warning: MouseListener interface will be used instead of it

This feature could be also useful in pair with CI servers (detect [WARNING] and make some additional actions).

The @JPredicate annotation generates Predicate implementation to use functional-way for programming. You can specify different predicate interfaces for implementation generation (JPredicateType):

• GUAVA - Guava predicates (com.google.common.base.Predicate)
• JAVA - predicates from Java 8 (java.util.function.Predicate)

There are several ways to generate predicate or group of predicates. It depends on the annotation location:

• annotation on field - generate predicate only for one specified field.
• annotation on method without args - generate predicate using method with empty list of arguments and non-void return-value.
• annotation on class - generate predicate using 2 previous strategies (for all fields and simple methods).

Original class Company:

public class Company {
    @JPredicate(reverse = true) private boolean listed;
}

Generated class CompanyPredicates:

public final class CompanyPredicates {
    public static final Predicate<Company> LISTED = new Predicate<Company>() {
        public boolean apply(final Company input) {
            return !input.isListed();
        }
    };
}

To generate reverse predicate, use parameter reverse.

There are some situations where you want to apply the same annotation to a declaration or type use. As of the Java SE 8 release, repeating annotations enable you to do this. If you don't/can't use Java 8, then @JRepeatable helps you to resolve this problem using extra list-annotation.

Original annotation @Role:

@JRepeatable
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.TYPE)
public @interface Role {
}

Generated annotation @RoleList:

@Retention(java.lang.annotation.RetentionPolicy.CLASS)
@Target(java.lang.annotation.ElementType.TYPE)
public @interface RoleList {
    Role[] value();
}

Java annotation processors and other systems use ServiceLoader to register implementations of well-known types using META-INF metadata. However, it is easy for a developer to forget to update or correctly specify the service descriptors. This annotation generates metadata for any class annotated with @JService.

Example:

public interface BaseType {}

@JService(BaseType.class)
public class TypeA implements BaseType {}

@JService(BaseType.class)
public class TypeB implements BaseType {}

Generated file META-INF/services/BaseType:

TypeA
TypeB

Jackdaw is based on APT processor which executes different code generators. Each code generator should implement interface CodeGenerator (or extends from BaseCodeGenerator / GeneratedCodeGenerator).

Signature of CodeGenerator interface:

public interface CodeGenerator {

    Class<? extends Annotation> getAnnotation();

    void generate(CodeGeneratorContext context) throws Exception;

    void onStart() throws Exception;

    void onFinish() throws Exception;

}

All generators are loaded by Java ServiceLoader mechanism, so you can add your custom generator in few steps:

• Create new generator class. It must have no-argument constructor.
• Create file META-INF/services/com.github.vbauer.jackdaw.code.base.CodeGenerator and put canonical name of you class in this file.

That's all!

Jackdaw uses Maven for its build. To build the complete project with all modules (including example project), run

mvn clean install

from the root of the project directory.

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• houdini - Type conversion system for Spring framework.
• herald - Logging annotation for Spring framework.
• commons-vfs2-cifs - SMB/CIFS provider for Commons VFS.
• avconv4java - Java interface to avconv tool.

Copyright 2015 Vladislav Bauer

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

See LICENSE file for details.