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Common utilities I find useful in many of my projects.

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package org.dstadler.commons.exec;

import org.apache.commons.exec.LogOutputStream;
import org.dstadler.commons.logging.jdk.LoggerFactory;

import java.io.IOException;
import java.util.logging.Logger;

/**
 * Implementation of the LogOutputStream from commons-exec which buffers
 * the log somewhat to not flood the output if there are many lines of text printed.
 *
 * It will print out all remaining data upon "close()".
 *
 * This class can be subclassed, e.g. to filter some lines from
 * processing.
 */
public class BufferingLogOutputStream extends LogOutputStream {
    private final static Logger log = LoggerFactory.make();

    /**
     * The max number of characters of output that are collected from the external application before reporting them to our log-system.
     *
     * A final flush is done at the end to capture all output.
     */
    private static final int LOG_FLUSH_LIMIT = 5000;

    private static final int LOG_FLUSH_TIME_LIMIT_SEC = 5;

    /**
     * Buffer for output from the external application. Constrained by {@link #LOG_FLUSH_LIMIT}
     */
    private final StringBuilder logBuffer = new StringBuilder();

    private long lastFlush = System.currentTimeMillis();

    @Override
    protected void processLine(String line, int level) {
        synchronized (logBuffer) {
            if(line != null && line.length() > 0) {
                logBuffer.append(line).append("\n");

                if(logBuffer.length() > LOG_FLUSH_LIMIT ||
                        lastFlush < (System.currentTimeMillis() - 1000*LOG_FLUSH_TIME_LIMIT_SEC)) {
                    log.info(logBuffer.toString());
                    logBuffer.setLength(0);
                    lastFlush = System.currentTimeMillis();
                }
            }
        }
    }

    /**
     * Flush any pending data in the {@link #logBuffer}
     * 
     * @throws IOException If closing the stream fails.
     */
    @Override
    public void close() throws IOException {
        // first close the parent so we get all remaining data
        super.close();

        // then ensure that any remaining buffer is logged
        synchronized (logBuffer) {
            if(logBuffer.length() > 0) {
                log.info(logBuffer.toString());
                logBuffer.setLength(0);
                lastFlush = System.currentTimeMillis();
            }
        }
    }
}