groovy-core/src/main/org/codehaus/groovy/control/io/AbstractReaderSource.java

/*
 * Copyright 2003-2007 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.control.io;

import java.io.BufferedReader;
import java.io.IOException;

import org.codehaus.groovy.control.CompilerConfiguration;
import org.codehaus.groovy.control.Janitor;

/**
 * For ReaderSources that can choose a parent class, a base that
 * provides common functionality.
 *
 * @author <a href="mailto:cpoirier@dreaming.org">Chris Poirier</a>
 * @version $Id$
 */

public abstract class AbstractReaderSource implements ReaderSource {
    protected CompilerConfiguration configuration;   // Configuration data

    public AbstractReaderSource(CompilerConfiguration configuration) {
        if (configuration == null) {
            throw new IllegalArgumentException("Compiler configuration must not be null!");
            // ... or more relaxed?
            // configuration = CompilerConfiguration.DEFAULT;
        }
        this.configuration = configuration;
    }

    /**
     * Returns true if the source can be restarted (ie. if getReader()
     * will return non-null on subsequent calls.
     */
    public boolean canReopenSource() {
        return true;
    }

    private BufferedReader lineSource = null;    // If set, a reader on the current source file
    private String line = null;    // The last line read from the current source file
    private int number = 0;       // The last line number read

    /**
     * Returns a line from the source, or null, if unavailable.  If
     * you supply a Janitor, resources will be cached.
     */
    public String getLine(int lineNumber, Janitor janitor) {
        // If the source is already open and is passed the line we
        // want, close it.
        if (lineSource != null && number > lineNumber) {
            cleanup();
        }

        // If the line source is closed, try to open it.
        if (lineSource == null) {
            try {
                lineSource = new BufferedReader(getReader());
            } catch (Exception e) {
                // Ignore
            }
            number = 0;
        }

        // Read until the appropriate line number.
        if (lineSource != null) {
            while (number < lineNumber) {
                try {
                    line = lineSource.readLine();
                    number++;
                }
                catch (IOException e) {
                    cleanup();
                }
            }

            if (janitor == null) {
                cleanup();
            } else {
                janitor.register(this);
            }
        }

        return line;
    }

    /**
     * Cleans up any cached resources used by getLine().
     */
    public void cleanup() {
        if (lineSource != null) {
            try {
                lineSource.close();
            } catch (Exception e) {
                // Ignore
            }
        }

        lineSource = null;
        line = null;
        number = 0;
    }

}