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Groovy example source code file (CategoryASTTransformation.java)

This example Groovy source code file (CategoryASTTransformation.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Groovy tags/keywords

annotationnode, classnode, classnode, closureexpression, expression, hashset, override, override, parameter, parameter, propertyexpression, this_expression, util, variableexpression, variableexpression

The Groovy CategoryASTTransformation.java source code

/*
 * Copyright 2008-2011 the original author or authors.
 *
 * 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.
 */

package org.codehaus.groovy.transform;

import org.codehaus.groovy.ast.stmt.CatchStatement;
import org.codehaus.groovy.control.CompilePhase;
import org.codehaus.groovy.control.SourceUnit;
import org.codehaus.groovy.control.messages.SyntaxErrorMessage;
import org.codehaus.groovy.ast.expr.*;
import org.codehaus.groovy.ast.stmt.BlockStatement;
import org.codehaus.groovy.ast.stmt.ExpressionStatement;
import org.codehaus.groovy.ast.stmt.ForStatement;
import org.codehaus.groovy.ast.*;
import org.codehaus.groovy.syntax.SyntaxException;
import org.objectweb.asm.Opcodes;

import groovy.lang.Reference;

import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

/**
 * Handles generation of code for the @Category annotation.
 * <p/>
 * Transformation logic is as follows:
 * <ul>
 * <li>all non-static methods converted to static ones with an additional 'self' parameter
 * <li>references to 'this' changed to the additional 'self' parameter
 * </ul>
 *
 * @author Alex Tkachman
 */
@GroovyASTTransformation(phase = CompilePhase.CANONICALIZATION)
public class CategoryASTTransformation implements ASTTransformation, Opcodes {
    private static final VariableExpression THIS_EXPRESSION;

    static {
        THIS_EXPRESSION = new VariableExpression("$this");
        THIS_EXPRESSION.setClosureSharedVariable(true);
    }

    /**
     * Property invocations done on 'this' reference are transformed so that the invocations at runtime are
     * done on the additional parameter 'self'
     */
    public void visit(ASTNode[] nodes, final SourceUnit source) {
        if (nodes.length != 2 || !(nodes[0] instanceof AnnotationNode) || !(nodes[1] instanceof ClassNode)) {
            throw new RuntimeException("Internal error: expecting [AnnotationNode, ClassNode] but got: " + Arrays.asList(nodes));
        }

        AnnotationNode annotation = (AnnotationNode) nodes[0];
        ClassNode parent = (ClassNode) nodes[1];

        ClassNode targetClass = getTargetClass(source, annotation);

        final LinkedList<Set varStack = new LinkedList>();
        Set<String> names = new HashSet();
        for (FieldNode field : parent.getFields()) {
            names.add(field.getName());
        }
        varStack.add(names);
        final Reference parameter = new Reference();
        final ClassCodeExpressionTransformer expressionTransformer = new ClassCodeExpressionTransformer() {
            protected SourceUnit getSourceUnit() {
                return source;
            }

            private void addVariablesToStack(Parameter[] params) {
                Set<String> names = new HashSet();
                names.addAll(varStack.getLast());
                for (Parameter param : params) {
                    names.add(param.getName());
                }
                varStack.add(names);
            }

            @Override
            public void visitCatchStatement(CatchStatement statement) {
                varStack.getLast().add(statement.getVariable().getName());
                super.visitCatchStatement(statement);
                varStack.getLast().remove(statement.getVariable().getName());
            }

            @Override
            public void visitMethod(MethodNode node) {
                addVariablesToStack(node.getParameters());
                super.visitMethod(node);
                varStack.removeLast();
            }

            @Override
            public void visitBlockStatement(BlockStatement block) {
                Set<String> names = new HashSet();
                names.addAll(varStack.getLast());
                varStack.add(names);
                super.visitBlockStatement(block);
                varStack.remove(names);
            }

            @Override
            public void visitClosureExpression(ClosureExpression ce) {
                addVariablesToStack(ce.getParameters());
                super.visitClosureExpression(ce);
                varStack.removeLast();
            }

            @Override
            public void visitDeclarationExpression(DeclarationExpression expression) {
                if (expression.isMultipleAssignmentDeclaration()) {
                    TupleExpression te = expression.getTupleExpression();
                    List<Expression> list = te.getExpressions();
                    for (Expression arg : list) {
                        VariableExpression ve = (VariableExpression) arg;
                        varStack.getLast().add(ve.getName());
                    }
                } else {
                    VariableExpression ve = expression.getVariableExpression();
                    varStack.getLast().add(ve.getName());
                }
                super.visitDeclarationExpression(expression);
            }

            @Override
            public void visitForLoop(ForStatement forLoop) {
                Expression exp = forLoop.getCollectionExpression();
                exp.visit(this);
                Parameter loopParam = forLoop.getVariable();
                if (loopParam != null) {
                    varStack.getLast().add(loopParam.getName());
                }
                super.visitForLoop(forLoop);
            }

            @Override
            public void visitExpressionStatement(ExpressionStatement es) {
                // GROOVY-3543: visit the declaration expressions so that declaration variables get added on the varStack
                Expression exp = es.getExpression();
                if (exp instanceof DeclarationExpression) {
                    exp.visit(this);
                }
                super.visitExpressionStatement(es);
            }

            @Override
            public Expression transform(Expression exp) {
                if (exp instanceof VariableExpression) {
                    VariableExpression ve = (VariableExpression) exp;
                    if (ve.getName().equals("this"))
                        return THIS_EXPRESSION;
                    else {
                        if (!varStack.getLast().contains(ve.getName())) {
                            return new PropertyExpression(THIS_EXPRESSION, ve.getName());
                        }
                    }
                } else if (exp instanceof PropertyExpression) {
                    PropertyExpression pe = (PropertyExpression) exp;
                    if (pe.getObjectExpression() instanceof VariableExpression) {
                        VariableExpression vex = (VariableExpression) pe.getObjectExpression();
                        if (vex.isThisExpression()) {
                            pe.setObjectExpression(THIS_EXPRESSION);
                            return pe;
                        }
                    }
                } else if (exp instanceof ClosureExpression) {
                    ClosureExpression ce = (ClosureExpression) exp;
                    ce.getVariableScope().putReferencedLocalVariable((Parameter) parameter.get());
                    Parameter[] params = ce.getParameters();
                    if (params == null) {
                        params = new Parameter[0];
                    } else if (params.length == 0) {
                        params = new Parameter[]{
                                new Parameter(ClassHelper.OBJECT_TYPE, "it")
                        };
                    }
                    addVariablesToStack(params);
                    ce.getCode().visit(this);
                    varStack.removeLast();
                }
                return super.transform(exp);
            }
        };

        for (MethodNode method : parent.getMethods()) {
            if (!method.isStatic()) {
                method.setModifiers(method.getModifiers() | Opcodes.ACC_STATIC);
                final Parameter[] origParams = method.getParameters();
                final Parameter[] newParams = new Parameter[origParams.length + 1];
                Parameter p = new Parameter(targetClass, "$this");
                p.setClosureSharedVariable(true);
                newParams[0] = p;
                parameter.set(p);
                System.arraycopy(origParams, 0, newParams, 1, origParams.length);
                method.setParameters(newParams);

                expressionTransformer.visitMethod(method);
            }
        }
    }

    private ClassNode getTargetClass(SourceUnit source, AnnotationNode annotation) {
        Expression value = annotation.getMember("value");
        if (value == null || !(value instanceof ClassExpression)) {
            //noinspection ThrowableInstanceNeverThrown
            source.getErrorCollector().addErrorAndContinue(
                    new SyntaxErrorMessage(new SyntaxException(
                            "@groovy.lang.Category must define 'value' which is the class to apply this category to",
                            annotation.getLineNumber(),
                            annotation.getColumnNumber()),
                            source));
            return null;
        } else {
            ClassExpression ce = (ClassExpression) value;
            return ce.getType();
        }
    }
}

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