StorageDisk.java

package org.apache.jdbm;

import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.OverlappingFileLockException;
import java.util.ArrayList;
import java.util.List;
import static org.apache.jdbm.StorageDiskMapped.*;

/**
 * Storage which used files on disk to store data
 */
class StorageDisk implements Storage {



    private ArrayList<RandomAccessFile> rafs = new ArrayList<RandomAccessFile>();
    private ArrayList<RandomAccessFile> rafsTranslation = new ArrayList<RandomAccessFile>();

    private String fileName;

    private long lastPageNumber = Long.MIN_VALUE;
    private boolean readonly;
    private boolean lockingDisabled;

    public StorageDisk(String fileName,boolean readonly, boolean lockingDisabled) throws IOException {
        this.fileName = fileName;
        this.readonly = readonly;
        this.lockingDisabled = lockingDisabled;
        //make sure first file can be opened
        //lock it
        try {
            if(!readonly && !lockingDisabled)
                getRaf(0).getChannel().tryLock();
        } catch (IOException e) {
            throw new IOException("Could not lock DB file: " + fileName, e);
        } catch (OverlappingFileLockException e) {
            throw new IOException("Could not lock DB file: " + fileName, e);
        }

    }

    RandomAccessFile getRaf(long pageNumber) throws IOException {

        int fileNumber = (int) (Math.abs(pageNumber)/PAGES_PER_FILE );

        List<RandomAccessFile> c = pageNumber>=0 ? rafs : rafsTranslation;

        //increase capacity of array lists if needed
        for (int i = c.size(); i <= fileNumber; i++) {
            c.add(null);
        }

        RandomAccessFile ret = c.get(fileNumber);
        if (ret == null) {
            String name = StorageDiskMapped.makeFileName(fileName, pageNumber, fileNumber);
            ret = new RandomAccessFile(name, readonly?"r":"rw");
            c.set(fileNumber, ret);
        }
        return ret;

    }


    public void write(long pageNumber, ByteBuffer data) throws IOException {
        if (data.capacity() != PAGE_SIZE) throw new IllegalArgumentException();
        
        long offset = pageNumber * PAGE_SIZE;

        RandomAccessFile file = getRaf(pageNumber);

//        if (lastPageNumber + 1 != pageNumber)      //TODO cache position again, so seek is not necessary
            file.seek(Math.abs(offset % (PAGES_PER_FILE* PAGE_SIZE)));

        file.write(data.array());
        lastPageNumber = pageNumber;
    }


    public ByteBuffer read(long pageNumber) throws IOException {
        
        long offset = pageNumber * PAGE_SIZE;
        ByteBuffer buffer = ByteBuffer.allocate(PAGE_SIZE);
        
        RandomAccessFile file = getRaf(pageNumber);
//        if (lastPageNumber + 1 != pageNumber) //TODO cache position again, so seek is not necessary
            file.seek(Math.abs(offset % (PAGES_PER_FILE* PAGE_SIZE)));
        int remaining = buffer.limit();
        int pos = 0;
        while (remaining > 0) {
            int read = file.read(buffer.array(), pos, remaining);
            if (read == -1) {
                System.arraycopy(PageFile.CLEAN_DATA, 0, buffer.array(), pos, remaining);
                break;
            }
            remaining -= read;
            pos += read;
        }
        lastPageNumber = pageNumber;
        return buffer;
    }


    static final String transaction_log_file_extension = ".t";


    public DataOutputStream openTransactionLog() throws IOException {
        String logName = fileName + transaction_log_file_extension;
        final FileOutputStream fileOut = new FileOutputStream(logName);
        return new DataOutputStream(new BufferedOutputStream(fileOut)) {

            //default implementation of flush on FileOutputStream does nothing,
            //so we use little workaround to make sure that data were really flushed
            public void flush() throws IOException {
                super.flush();
                fileOut.flush();
                fileOut.getFD().sync();
            }
        };
    }

    public void deleteAllFiles() {
        deleteTransactionLog();
        StorageDiskMapped.deleteFiles(fileName);
    }


    /**
     * Synchronizes the file.
     */
    public void sync() throws IOException {
        for (RandomAccessFile file : rafs)
            if (file != null)
                file.getFD().sync();
        for (RandomAccessFile file : rafsTranslation)
            if (file != null)
                file.getFD().sync();
    }

    public void forceClose() throws IOException {
        for (RandomAccessFile f : rafs) {
            if (f != null)
                f.close();
        }
        rafs = null;
        for (RandomAccessFile f : rafsTranslation) {
            if (f != null)
                f.close();
        }
        rafsTranslation = null;
    }


    public DataInputStream readTransactionLog() {

        File logFile = new File(fileName + transaction_log_file_extension);
        if (!logFile.exists())
            return null;
        if (logFile.length() == 0) {
            logFile.delete();
            return null;
        }

        DataInputStream ois = null;
        try {
            ois = new DataInputStream(new BufferedInputStream(new FileInputStream(logFile)));
        } catch (FileNotFoundException e) {
            //file should exists, we check for its presents just a miliseconds yearlier, anyway move on
            return null;
        }

        try {
            if (ois.readShort() != Magic.LOGFILE_HEADER)
                throw new Error("Bad magic on log file");
        } catch (IOException e) {
            // corrupted/empty logfile
            logFile.delete();
            return null;
        }
        return ois;
    }

    public void deleteTransactionLog() {
        File logFile = new File(fileName + transaction_log_file_extension);
        if (logFile.exists())
            logFile.delete();
    }

    public boolean isReadonly() {
        return false;
    }
}