de.flapdoodle.logparser.streamlistener.OnceAndOnlyOnceStreamListener.java Source code

Introduction

Here is the source code for de.flapdoodle.logparser.streamlistener.OnceAndOnlyOnceStreamListener.java

Source

/**
 * Copyright (C) 2013
 *   Michael Mosmann <michael@mosmann.de>
 *
 * with contributions from
 *    ${lic.developers}
 *
 * 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 de.flapdoodle.logparser.streamlistener;

import com.google.common.base.Optional;

import de.flapdoodle.logparser.IStreamListener;

public class OnceAndOnlyOnceStreamListener<T> implements IStreamListener<T> {

    boolean firstCall = true;
    private T _value;

    @Override
    public void entry(T value) {
        if (!firstCall)
            throw new IllegalArgumentException("called more than once: [" + _value + "]");

        firstCall = false;
        _value = value;
    }

    public Optional<T> value() {
        return Optional.fromNullable(_value);
    }

}