Bitmap_图片硬盘缓存（3）

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我是靠谱客的博主寂寞钢笔，最近开发中收集的这篇文章主要介绍Bitmap_图片硬盘缓存（3），觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

前两章回顾了 BItmap 图片压缩和内存缓存相关的知识，今天把图片的硬盘缓存记录下，下一篇讲的就是图片的加载，使用多级缓存技术。虽然当前的图片加载已经日新月异，为什么还要去自己弄呢？工具是别人的，知识是自己的，只有自己掌握了，谁也抢不走。

上代码：

先是几个工具类：也可以直接去下载DiskLruCache相关的jar包，或者直接把当前的类拷贝过来。我就不用拷贝jar包了，直接把类拷贝过来，

package image.reeman.com.imageloader;

import java.io.BufferedWriter;
import java.io.Closeable;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


public final class DiskLruCache implements Closeable {
    static final String JOURNAL_FILE = "journal";
    static final String JOURNAL_FILE_TEMP = "journal.tmp";
    static final String JOURNAL_FILE_BACKUP = "journal.bkp";
    static final String MAGIC = "libcore.io.DiskLruCache";
    static final String VERSION_1 = "1";
    static final long ANY_SEQUENCE_NUMBER = -1;
    static final String STRING_KEY_PATTERN = "[a-z0-9_-]{1,120}";
    static final Pattern LEGAL_KEY_PATTERN = Pattern.compile(STRING_KEY_PATTERN);
    private static final String CLEAN = "CLEAN";
    private static final String DIRTY = "DIRTY";
    private static final String REMOVE = "REMOVE";
    private static final String READ = "READ";

    

    private final File directory;
    private final File journalFile;
    private final File journalFileTmp;
    private final File journalFileBackup;
    private final int appVersion;
    private long maxSize;
    private final int valueCount;
    private long size = 0;
    private Writer journalWriter;
    private final LinkedHashMap<String, Entry> lruEntries =
            new LinkedHashMap<String, Entry>(0, 0.75f, true);
    private int redundantOpCount;

    /**
     * To differentiate between old and current snapshots, each entry is given
     * a sequence number each time an edit is committed. A snapshot is stale if
     * its sequence number is not equal to its entry's sequence number.
     */
    private long nextSequenceNumber = 0;

    /**
     * This cache uses a single background thread to evict entries.
     */
    final ThreadPoolExecutor executorService =
            new ThreadPoolExecutor(0, 1, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
    private final Callable<Void> cleanupCallable = new Callable<Void>() {
        public Void call() throws Exception {
            synchronized (DiskLruCache.this) {
                if (journalWriter == null) {
                    return null; // Closed.
                }
                trimToSize();
                if (journalRebuildRequired()) {
                    rebuildJournal();
                    redundantOpCount = 0;
                }
            }
            return null;
        }
    };

    private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {
        this.directory = directory;
        this.appVersion = appVersion;
        this.journalFile = new File(directory, JOURNAL_FILE);
        this.journalFileTmp = new File(directory, JOURNAL_FILE_TEMP);
        this.journalFileBackup = new File(directory, JOURNAL_FILE_BACKUP);
        this.valueCount = valueCount;
        this.maxSize = maxSize;
    }

    /**
     * Opens the cache in {@code directory}, creating a cache if none exists
     * there.
     *
     * @param directory  a writable directory
     * @param valueCount the number of values per cache entry. Must be positive.
     * @param maxSize    the maximum number of bytes this cache should use to store
     * @throws IOException if reading or writing the cache directory fails
     */
    public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)
            throws IOException {
        if (maxSize <= 0) {
            throw new IllegalArgumentException("maxSize <= 0");
        }
        if (valueCount <= 0) {
            throw new IllegalArgumentException("valueCount <= 0");
        }

        // If a bkp file exists, use it instead.
        File backupFile = new File(directory, JOURNAL_FILE_BACKUP);
        if (backupFile.exists()) {
            File journalFile = new File(directory, JOURNAL_FILE);
            // If journal file also exists just delete backup file.
            if (journalFile.exists()) {
                backupFile.delete();
            } else {
                renameTo(backupFile, journalFile, false);
            }
        }

        // Prefer to pick up where we left off.
        DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
        if (cache.journalFile.exists()) {
            try {
                cache.readJournal();
                cache.processJournal();
                return cache;
            } catch (IOException journalIsCorrupt) {
                System.out
                        .println("DiskLruCache "
                                + directory
                                + " is corrupt: "
                                + journalIsCorrupt.getMessage()
                                + ", removing");
                cache.delete();
            }
        }

        // Create a new empty cache.
        directory.mkdirs();
        cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
        cache.rebuildJournal();
        return cache;
    }

    private void readJournal() throws IOException {
        StrictLineReader reader = new StrictLineReader(new FileInputStream(journalFile), Util.US_ASCII);
        try {
            String magic = reader.readLine();
            String version = reader.readLine();
            String appVersionString = reader.readLine();
            String valueCountString = reader.readLine();
            String blank = reader.readLine();
            if (!MAGIC.equals(magic)
                    || !VERSION_1.equals(version)
                    || !Integer.toString(appVersion).equals(appVersionString)
                    || !Integer.toString(valueCount).equals(valueCountString)
                    || !"".equals(blank)) {
                throw new IOException("unexpected journal header: [" + magic + ", " + version + ", "
                        + valueCountString + ", " + blank + "]");
            }

            int lineCount = 0;
            while (true) {
                try {
                    readJournalLine(reader.readLine());
                    lineCount++;
                } catch (EOFException endOfJournal) {
                    break;
                }
            }
            redundantOpCount = lineCount - lruEntries.size();

            // If we ended on a truncated line, rebuild the journal before appending to it.
            if (reader.hasUnterminatedLine()) {
                rebuildJournal();
            } else {
                journalWriter = new BufferedWriter(new OutputStreamWriter(
                        new FileOutputStream(journalFile, true), Util.US_ASCII));
            }
        } finally {
            Util.closeQuietly(reader);
        }
    }

    private void readJournalLine(String line) throws IOException {
        int firstSpace = line.indexOf(' ');
        if (firstSpace == -1) {
            throw new IOException("unexpected journal line: " + line);
        }

        int keyBegin = firstSpace + 1;
        int secondSpace = line.indexOf(' ', keyBegin);
        final String key;
        if (secondSpace == -1) {
            key = line.substring(keyBegin);
            if (firstSpace == REMOVE.length() && line.startsWith(REMOVE)) {
                lruEntries.remove(key);
                return;
            }
        } else {
            key = line.substring(keyBegin, secondSpace);
        }

        Entry entry = lruEntries.get(key);
        if (entry == null) {
            entry = new Entry(key);
            lruEntries.put(key, entry);
        }

        if (secondSpace != -1 && firstSpace == CLEAN.length() && line.startsWith(CLEAN)) {
            String[] parts = line.substring(secondSpace + 1).split(" ");
            entry.readable = true;
            entry.currentEditor = null;
            entry.setLengths(parts);
        } else if (secondSpace == -1 && firstSpace == DIRTY.length() && line.startsWith(DIRTY)) {
            entry.currentEditor = new Editor(entry);
        } else if (secondSpace == -1 && firstSpace == READ.length() && line.startsWith(READ)) {
            // This work was already done by calling lruEntries.get().
        } else {
            throw new IOException("unexpected journal line: " + line);
        }
    }

    /**
     * Computes the initial size and collects garbage as a part of opening the
     * cache. Dirty entries are assumed to be inconsistent and will be deleted.
     */
    private void processJournal() throws IOException {
        deleteIfExists(journalFileTmp);
        for (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); ) {
            Entry entry = i.next();
            if (entry.currentEditor == null) {
                for (int t = 0; t < valueCount; t++) {
                    size += entry.lengths[t];
                }
            } else {
                entry.currentEditor = null;
                for (int t = 0; t < valueCount; t++) {
                    deleteIfExists(entry.getCleanFile(t));
                    deleteIfExists(entry.getDirtyFile(t));
                }
                i.remove();
            }
        }
    }

    /**
     * Creates a new journal that omits redundant information. This replaces the
     * current journal if it exists.
     */
    private synchronized void rebuildJournal() throws IOException {
        if (journalWriter != null) {
            journalWriter.close();
        }

        Writer writer = new BufferedWriter(
                new OutputStreamWriter(new FileOutputStream(journalFileTmp), Util.US_ASCII));
        try {
            writer.write(MAGIC);
            writer.write("n");
            writer.write(VERSION_1);
            writer.write("n");
            writer.write(Integer.toString(appVersion));
            writer.write("n");
            writer.write(Integer.toString(valueCount));
            writer.write("n");
            writer.write("n");

            for (Entry entry : lruEntries.values()) {
                if (entry.currentEditor != null) {
                    writer.write(DIRTY + ' ' + entry.key + 'n');
                } else {
                    writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + 'n');
                }
            }
        } finally {
            writer.close();
        }

        if (journalFile.exists()) {
            renameTo(journalFile, journalFileBackup, true);
        }
        renameTo(journalFileTmp, journalFile, false);
        journalFileBackup.delete();

        journalWriter = new BufferedWriter(
                new OutputStreamWriter(new FileOutputStream(journalFile, true), Util.US_ASCII));
    }

    private static void deleteIfExists(File file) throws IOException {
        if (file.exists() && !file.delete()) {
            throw new IOException();
        }
    }

    private static void renameTo(File from, File to, boolean deleteDestination) throws IOException {
        if (deleteDestination) {
            deleteIfExists(to);
        }
        if (!from.renameTo(to)) {
            throw new IOException();
        }
    }

    /**
     * Returns a snapshot of the entry named {@code key}, or null if it doesn't
     * exist is not currently readable. If a value is returned, it is moved to
     * the head of the LRU queue.
     */
    public synchronized Snapshot get(String key) throws IOException {
        checkNotClosed();
        validateKey(key);
        Entry entry = lruEntries.get(key);
        if (entry == null) {
            return null;
        }

        if (!entry.readable) {
            return null;
        }

        // Open all streams eagerly to guarantee that we see a single published
        // snapshot. If we opened streams lazily then the streams could come
        // from different edits.
        InputStream[] ins = new InputStream[valueCount];
        try {
            for (int i = 0; i < valueCount; i++) {
                ins[i] = new FileInputStream(entry.getCleanFile(i));
            }
        } catch (FileNotFoundException e) {
            // A file must have been deleted manually!
            for (int i = 0; i < valueCount; i++) {
                if (ins[i] != null) {
                    Util.closeQuietly(ins[i]);
                } else {
                    break;
                }
            }
            return null;
        }

        redundantOpCount++;
        journalWriter.append(READ + ' ' + key + 'n');
        if (journalRebuildRequired()) {
            executorService.submit(cleanupCallable);
        }

        return new Snapshot(key, entry.sequenceNumber, ins, entry.lengths);
    }

    /**
     * Returns an editor for the entry named {@code key}, or null if another
     * edit is in progress.
     */
    public Editor edit(String key) throws IOException {
        return edit(key, ANY_SEQUENCE_NUMBER);
    }

    private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {
        checkNotClosed();
        validateKey(key);
        Entry entry = lruEntries.get(key);
        if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER && (entry == null
                || entry.sequenceNumber != expectedSequenceNumber)) {
            return null; // Snapshot is stale.
        }
        if (entry == null) {
            entry = new Entry(key);
            lruEntries.put(key, entry);
        } else if (entry.currentEditor != null) {
            return null; // Another edit is in progress.
        }

        Editor editor = new Editor(entry);
        entry.currentEditor = editor;

        // Flush the journal before creating files to prevent file leaks.
        journalWriter.write(DIRTY + ' ' + key + 'n');
        journalWriter.flush();
        return editor;
    }

    /**
     * Returns the directory where this cache stores its data.
     */
    public File getDirectory() {
        return directory;
    }

    /**
     * Returns the maximum number of bytes that this cache should use to store
     * its data.
     */
    public synchronized long getMaxSize() {
        return maxSize;
    }

    /**
     * Changes the maximum number of bytes the cache can store and queues a job
     * to trim the existing store, if necessary.
     */
    public synchronized void setMaxSize(long maxSize) {
        this.maxSize = maxSize;
        executorService.submit(cleanupCallable);
    }

    /**
     * Returns the number of bytes currently being used to store the values in
     * this cache. This may be greater than the max size if a background
     * deletion is pending.
     */
    public synchronized long size() {
        return size;
    }

    private synchronized void completeEdit(Editor editor, boolean success) throws IOException {
        Entry entry = editor.entry;
        if (entry.currentEditor != editor) {
            throw new IllegalStateException();
        }

        // If this edit is creating the entry for the first time, every index must have a value.
        if (success && !entry.readable) {
            for (int i = 0; i < valueCount; i++) {
                if (!editor.written[i]) {
                    editor.abort();
                    throw new IllegalStateException("Newly created entry didn't create value for index " + i);
                }
                if (!entry.getDirtyFile(i).exists()) {
                    editor.abort();
                    return;
                }
            }
        }

        for (int i = 0; i < valueCount; i++) {
            File dirty = entry.getDirtyFile(i);
            if (success) {
                if (dirty.exists()) {
                    File clean = entry.getCleanFile(i);
                    dirty.renameTo(clean);
                    long oldLength = entry.lengths[i];
                    long newLength = clean.length();
                    entry.lengths[i] = newLength;
                    size = size - oldLength + newLength;
                }
            } else {
                deleteIfExists(dirty);
            }
        }

        redundantOpCount++;
        entry.currentEditor = null;
        if (entry.readable | success) {
            entry.readable = true;
            journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + 'n');
            if (success) {
                entry.sequenceNumber = nextSequenceNumber++;
            }
        } else {
            lruEntries.remove(entry.key);
            journalWriter.write(REMOVE + ' ' + entry.key + 'n');
        }
        journalWriter.flush();

        if (size > maxSize || journalRebuildRequired()) {
            executorService.submit(cleanupCallable);
        }
    }

    /**
     * We only rebuild the journal when it will halve the size of the journal
     * and eliminate at least 2000 ops.
     */
    private boolean journalRebuildRequired() {
        final int redundantOpCompactThreshold = 2000;
        return redundantOpCount >= redundantOpCompactThreshold //
                && redundantOpCount >= lruEntries.size();
    }

    /**
     * Drops the entry for {@code key} if it exists and can be removed. Entries
     * actively being edited cannot be removed.
     *
     * @return true if an entry was removed.
     */
    public synchronized boolean remove(String key) throws IOException {
        checkNotClosed();
        validateKey(key);
        Entry entry = lruEntries.get(key);
        if (entry == null || entry.currentEditor != null) {
            return false;
        }

        for (int i = 0; i < valueCount; i++) {
            File file = entry.getCleanFile(i);
            if (file.exists() && !file.delete()) {
                throw new IOException("failed to delete " + file);
            }
            size -= entry.lengths[i];
            entry.lengths[i] = 0;
        }

        redundantOpCount++;
        journalWriter.append(REMOVE + ' ' + key + 'n');
        lruEntries.remove(key);

        if (journalRebuildRequired()) {
            executorService.submit(cleanupCallable);
        }

        return true;
    }

    /**
     * Returns true if this cache has been closed.
     */
    public synchronized boolean isClosed() {
        return journalWriter == null;
    }

    private void checkNotClosed() {
        if (journalWriter == null) {
            throw new IllegalStateException("cache is closed");
        }
    }

    /**
     * Force buffered operations to the filesystem.
     */
    public synchronized void flush() throws IOException {
        checkNotClosed();
        trimToSize();
        journalWriter.flush();
    }

    /**
     * Closes this cache. Stored values will remain on the filesystem.
     */
    public synchronized void close() throws IOException {
        if (journalWriter == null) {
            return; // Already closed.
        }
        for (Entry entry : new ArrayList<Entry>(lruEntries.values())) {
            if (entry.currentEditor != null) {
                entry.currentEditor.abort();
            }
        }
        trimToSize();
        journalWriter.close();
        journalWriter = null;
    }

    private void trimToSize() throws IOException {
        while (size > maxSize) {
            Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next();
            remove(toEvict.getKey());
        }
    }

    /**
     * Closes the cache and deletes all of its stored values. This will delete
     * all files in the cache directory including files that weren't created by
     * the cache.
     */
    public void delete() throws IOException {
        close();
        Util.deleteContents(directory);
    }

    private void validateKey(String key) {
        Matcher matcher = LEGAL_KEY_PATTERN.matcher(key);
        if (!matcher.matches()) {
            throw new IllegalArgumentException("keys must match regex "
                    + STRING_KEY_PATTERN + ": "" + key + """);
        }
    }

    private static String inputStreamToString(InputStream in) throws IOException {
        return Util.readFully(new InputStreamReader(in, Util.UTF_8));
    }

    /**
     * A snapshot of the values for an entry.
     */
    public final class Snapshot implements Closeable {
        private final String key;
        private final long sequenceNumber;
        private final InputStream[] ins;
        private final long[] lengths;

        private Snapshot(String key, long sequenceNumber, InputStream[] ins, long[] lengths) {
            this.key = key;
            this.sequenceNumber = sequenceNumber;
            this.ins = ins;
            this.lengths = lengths;
        }

        /**
         * Returns an editor for this snapshot's entry, or null if either the
         * entry has changed since this snapshot was created or if another edit
         * is in progress.
         */
        public Editor edit() throws IOException {
            return DiskLruCache.this.edit(key, sequenceNumber);
        }

        /**
         * Returns the unbuffered stream with the value for {@code index}.
         */
        public InputStream getInputStream(int index) {
            return ins[index];
        }

        /**
         * Returns the string value for {@code index}.
         */
        public String getString(int index) throws IOException {
            return inputStreamToString(getInputStream(index));
        }

        /**
         * Returns the byte length of the value for {@code index}.
         */
        public long getLength(int index) {
            return lengths[index];
        }

        public void close() {
            for (InputStream in : ins) {
                Util.closeQuietly(in);
            }
        }
    }

    private static final OutputStream NULL_OUTPUT_STREAM = new OutputStream() {
        @Override
        public void write(int b) throws IOException {
            // Eat all writes silently. Nom nom.
        }
    };

    /**
     * Edits the values for an entry.
     */
    public final class Editor {
        private final Entry entry;
        private final boolean[] written;
        private boolean hasErrors;
        private boolean committed;

        private Editor(Entry entry) {
            this.entry = entry;
            this.written = (entry.readable) ? null : new boolean[valueCount];
        }

        /**
         * Returns an unbuffered input stream to read the last committed value,
         * or null if no value has been committed.
         */
        public InputStream newInputStream(int index) throws IOException {
            synchronized (DiskLruCache.this) {
                if (entry.currentEditor != this) {
                    throw new IllegalStateException();
                }
                if (!entry.readable) {
                    return null;
                }
                try {
                    return new FileInputStream(entry.getCleanFile(index));
                } catch (FileNotFoundException e) {
                    return null;
                }
            }
        }

        /**
         * Returns the last committed value as a string, or null if no value
         * has been committed.
         */
        public String getString(int index) throws IOException {
            InputStream in = newInputStream(index);
            return in != null ? inputStreamToString(in) : null;
        }

        /**
         * Returns a new unbuffered output stream to write the value at
         * {@code index}. If the underlying output stream encounters errors
         * when writing to the filesystem, this edit will be aborted when
         * {@link #commit} is called. The returned output stream does not throw
         * IOExceptions.
         */
        public OutputStream newOutputStream(int index) throws IOException {
            if (index < 0 || index >= valueCount) {
                throw new IllegalArgumentException("Expected index " + index + " to "
                        + "be greater than 0 and less than the maximum value count "
                        + "of " + valueCount);
            }
            synchronized (DiskLruCache.this) {
                if (entry.currentEditor != this) {
                    throw new IllegalStateException();
                }
                if (!entry.readable) {
                    written[index] = true;
                }
                File dirtyFile = entry.getDirtyFile(index);
                FileOutputStream outputStream;
                try {
                    outputStream = new FileOutputStream(dirtyFile);
                } catch (FileNotFoundException e) {
                    // Attempt to recreate the cache directory.
                    directory.mkdirs();
                    try {
                        outputStream = new FileOutputStream(dirtyFile);
                    } catch (FileNotFoundException e2) {
                        // We are unable to recover. Silently eat the writes.
                        return NULL_OUTPUT_STREAM;
                    }
                }
                return new FaultHidingOutputStream(outputStream);
            }
        }

        /**
         * Sets the value at {@code index} to {@code value}.
         */
        public void set(int index, String value) throws IOException {
            Writer writer = null;
            try {
                writer = new OutputStreamWriter(newOutputStream(index), Util.UTF_8);
                writer.write(value);
            } finally {
                Util.closeQuietly(writer);
            }
        }

        /**
         * Commits this edit so it is visible to readers.  This releases the
         * edit lock so another edit may be started on the same key.
         */
        public void commit() throws IOException {
            if (hasErrors) {
                completeEdit(this, false);
                remove(entry.key); // The previous entry is stale.
            } else {
                completeEdit(this, true);
            }
            committed = true;
        }

        /**
         * Aborts this edit. This releases the edit lock so another edit may be
         * started on the same key.
         */
        public void abort() throws IOException {
            completeEdit(this, false);
        }

        public void abortUnlessCommitted() {
            if (!committed) {
                try {
                    abort();
                } catch (IOException ignored) {
                }
            }
        }

        private class FaultHidingOutputStream extends FilterOutputStream {
            private FaultHidingOutputStream(OutputStream out) {
                super(out);
            }

            @Override
            public void write(int oneByte) {
                try {
                    out.write(oneByte);
                } catch (IOException e) {
                    hasErrors = true;
                }
            }

            @Override
            public void write(byte[] buffer, int offset, int length) {
                try {
                    out.write(buffer, offset, length);
                } catch (IOException e) {
                    hasErrors = true;
                }
            }

            @Override
            public void close() {
                try {
                    out.close();
                } catch (IOException e) {
                    hasErrors = true;
                }
            }

            @Override
            public void flush() {
                try {
                    out.flush();
                } catch (IOException e) {
                    hasErrors = true;
                }
            }
        }
    }

    private final class Entry {
        private final String key;

        /**
         * Lengths of this entry's files.
         */
        private final long[] lengths;

        /**
         * True if this entry has ever been published.
         */
        private boolean readable;

        /**
         * The ongoing edit or null if this entry is not being edited.
         */
        private Editor currentEditor;

        /**
         * The sequence number of the most recently committed edit to this entry.
         */
        private long sequenceNumber;

        private Entry(String key) {
            this.key = key;
            this.lengths = new long[valueCount];
        }

        public String getLengths() throws IOException {
            StringBuilder result = new StringBuilder();
            for (long size : lengths) {
                result.append(' ').append(size);
            }
            return result.toString();
        }

        /**
         * Set lengths using decimal numbers like "10123".
         */
        private void setLengths(String[] strings) throws IOException {
            if (strings.length != valueCount) {
                throw invalidLengths(strings);
            }

            try {
                for (int i = 0; i < strings.length; i++) {
                    lengths[i] = Long.parseLong(strings[i]);
                }
            } catch (NumberFormatException e) {
                throw invalidLengths(strings);
            }
        }

        private IOException invalidLengths(String[] strings) throws IOException {
            throw new IOException("unexpected journal line: " + java.util.Arrays.toString(strings));
        }

        public File getCleanFile(int i) {
            return new File(directory, key + "." + i);
        }

        public File getDirtyFile(int i) {
            return new File(directory, key + "." + i + ".tmp");
        }
    }
}

工具类2

package image.reeman.com.imageloader;

import java.io.ByteArrayOutputStream;
import java.io.Closeable;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
 
class StrictLineReader implements Closeable {
    private static final byte CR = (byte) 'r';
    private static final byte LF = (byte) 'n';

    private final InputStream in;
    private final Charset charset;

    /*
     * Buffered data is stored in {@code buf}. As long as no exception occurs, 0 <= pos <= end
     * and the data in the range [pos, end) is buffered for reading. At end of input, if there is
     * an unterminated line, we set end == -1, otherwise end == pos. If the underlying
     * {@code InputStream} throws an {@code IOException}, end may remain as either pos or -1.
     */
    private byte[] buf;
    private int pos;
    private int end;

    /**
     * Constructs a new {@code LineReader} with the specified charset and the default capacity.
     *
     * @param in      the {@code InputStream} to read data from.
     * @param charset the charset used to decode data. Only US-ASCII, UTF-8 and ISO-8859-1 are
     *                supported.
     * @throws NullPointerException     if {@code in} or {@code charset} is null.
     * @throws IllegalArgumentException if the specified charset is not supported.
     */
    public StrictLineReader(InputStream in, Charset charset) {
        this(in, 8192, charset);
    }

    /**
     * Constructs a new {@code LineReader} with the specified capacity and charset.
     *
     * @param in       the {@code InputStream} to read data from.
     * @param capacity the capacity of the buffer.
     * @param charset  the charset used to decode data. Only US-ASCII, UTF-8 and ISO-8859-1 are
     *                 supported.
     * @throws NullPointerException     if {@code in} or {@code charset} is null.
     * @throws IllegalArgumentException if {@code capacity} is negative or zero
     *                                  or the specified charset is not supported.
     */
    public StrictLineReader(InputStream in, int capacity, Charset charset) {
        if (in == null || charset == null) {
            throw new NullPointerException();
        }
        if (capacity < 0) {
            throw new IllegalArgumentException("capacity <= 0");
        }
        if (!(charset.equals(Util.US_ASCII))) {
            throw new IllegalArgumentException("Unsupported encoding");
        }

        this.in = in;
        this.charset = charset;
        buf = new byte[capacity];
    }

    /**
     * Closes the reader by closing the underlying {@code InputStream} and
     * marking this reader as closed.
     *
     * @throws IOException for errors when closing the underlying {@code InputStream}.
     */
    public void close() throws IOException {
        synchronized (in) {
            if (buf != null) {
                buf = null;
                in.close();
            }
        }
    }

    /**
     * Reads the next line. A line ends with {@code "n"} or {@code "rn"},
     * this end of line marker is not included in the result.
     *
     * @return the next line from the input.
     * @throws IOException  for underlying {@code InputStream} errors.
     * @throws EOFException for the end of source stream.
     */
    public String readLine() throws IOException {
        synchronized (in) {
            if (buf == null) {
                throw new IOException("LineReader is closed");
            }

            // Read more data if we are at the end of the buffered data.
            // Though it's an error to read after an exception, we will let {@code fillBuf()}
            // throw again if that happens; thus we need to handle end == -1 as well as end == pos.
            if (pos >= end) {
                fillBuf();
            }
            // Try to find LF in the buffered data and return the line if successful.
            for (int i = pos; i != end; ++i) {
                if (buf[i] == LF) {
                    int lineEnd = (i != pos && buf[i - 1] == CR) ? i - 1 : i;
                    String res = new String(buf, pos, lineEnd - pos, charset.name());
                    pos = i + 1;
                    return res;
                }
            }

            // Let's anticipate up to 80 characters on top of those already read.
            ByteArrayOutputStream out = new ByteArrayOutputStream(end - pos + 80) {
                @Override
                public String toString() {
                    int length = (count > 0 && buf[count - 1] == CR) ? count - 1 : count;
                    try {
                        return new String(buf, 0, length, charset.name());
                    } catch (UnsupportedEncodingException e) {
                        throw new AssertionError(e); // Since we control the charset this will never happen.
                    }
                }
            };

            while (true) {
                out.write(buf, pos, end - pos);
                // Mark unterminated line in case fillBuf throws EOFException or IOException.
                end = -1;
                fillBuf();
                // Try to find LF in the buffered data and return the line if successful.
                for (int i = pos; i != end; ++i) {
                    if (buf[i] == LF) {
                        if (i != pos) {
                            out.write(buf, pos, i - pos);
                        }
                        pos = i + 1;
                        return out.toString();
                    }
                }
            }
        }
    }

    public boolean hasUnterminatedLine() {
        return end == -1;
    }

    /**
     * Reads new input data into the buffer. Call only with pos == end or end == -1,
     * depending on the desired outcome if the function throws.
     */
    private void fillBuf() throws IOException {
        int result = in.read(buf, 0, buf.length);
        if (result == -1) {
            throw new EOFException();
        }
        pos = 0;
        end = result;
    }
}

工具类三，

package image.reeman.com.imageloader;

import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.io.Reader;
import java.io.StringWriter;
import java.nio.charset.Charset;

/**
 * Junk drawer of utility methods.
 */
final class Util {
    static final Charset US_ASCII = Charset.forName("US-ASCII");
    static final Charset UTF_8 = Charset.forName("UTF-8");

    private Util() {
    }

    static String readFully(Reader reader) throws IOException {
        try {
            StringWriter writer = new StringWriter();
            char[] buffer = new char[1024];
            int count;
            while ((count = reader.read(buffer)) != -1) {
                writer.write(buffer, 0, count);
            }
            return writer.toString();
        } finally {
            reader.close();
        }
    }

    /**
     * Deletes the contents of {@code dir}. Throws an IOException if any file
     * could not be deleted, or if {@code dir} is not a readable directory.
     */
    static void deleteContents(File dir) throws IOException {
        File[] files = dir.listFiles();
        if (files == null) {
            throw new IOException("not a readable directory: " + dir);
        }
        for (File file : files) {
            if (file.isDirectory()) {
                deleteContents(file);
            }
            if (!file.delete()) {
                throw new IOException("failed to delete file: " + file);
            }
        }
    }

    static void closeQuietly(/*Auto*/Closeable closeable) {
        if (closeable != null) {
            try {
                closeable.close();
            } catch (RuntimeException rethrown) {
                throw rethrown;
            } catch (Exception ignored) {
            }
        }
    }
}

MD5加密解密的工具类

package image.reeman.com.imageloader;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * Created by Administrator on 2017/7/9.
 */

public class MD5 {


    /***
     * 用来将字符串进行MD5编码
     * @param key
     * @return
     */
    public static String hashKeyForDisk(String key) {
        String cacheKey;
        try {
            final MessageDigest mDigest = MessageDigest.getInstance("MD5");
            mDigest.update(key.getBytes());
            cacheKey = bytesToHexString(mDigest.digest());
        } catch (NoSuchAlgorithmException e) {
            cacheKey = String.valueOf(key.hashCode());
        }
        return cacheKey;
    }

    public static String bytesToHexString(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < bytes.length; i++) {
            String hex = Integer.toHexString(0xFF & bytes[i]);
            if (hex.length() == 1) {
                sb.append('0');
            }
            sb.append(hex);
        }
        return sb.toString();
    }

}

硬盘缓存的工具类，里面写入了一些初始化，添加图片到缓存，从缓存取图片的方法

package image.reeman.com.imageloader;

import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;


public class DiskCacheUtil {

    Context context;
    DiskLruCache mDiskLruCache;

    public DiskCacheUtil(Context context) {
        this.context = context.getApplicationContext();
        try {
            File cacheDir = getDiskCacheDir(context, "bitmap");
            if (!cacheDir.exists()) {
                cacheDir.mkdirs();
            }
            //硬盘缓存初始化是不可以new 的，
            //四个参数分别是，1：缓存路径，2：当前软件版本 3：图片个数默认1  4：图片最大的内存
            mDiskLruCache = DiskLruCache.open(cacheDir, getAppVersion(context), 1, 10 * 1024 * 1024);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /***
     * 保存网络图片到硬盘缓存
     */
    public void saveBitmapToDisk() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    String imageUrl = "https://img-my.csdn.net/uploads/201309/01/1378037235_7476.jpg";
                    String key = MD5.hashKeyForDisk(imageUrl);
                    DiskLruCache.Editor editor = mDiskLruCache.edit(key);
                    if (editor != null) {
                        OutputStream outputStream = editor.newOutputStream(0);
                        if (downloadUrlToStream(imageUrl, outputStream)) {
                            editor.commit();
                        } else {
                            editor.abort();
                        }
                    }
                    mDiskLruCache.flush();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }


    /***
     * 从硬盘缓存中取照片
     * @return
     */
    public Bitmap getBitmapFromDisk() {
        Bitmap bitmap = null;
        try {
            String imageUrl = "https://img-my.csdn.net/uploads/201309/01/1378037235_7476.jpg";
            String key = MD5.hashKeyForDisk(imageUrl);
            DiskLruCache.Snapshot snapShot = mDiskLruCache.get(key);
            if (snapShot != null) {
                InputStream is = snapShot.getInputStream(0);
                bitmap = BitmapFactory.decodeStream(is);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return bitmap;
    }

    /***
     * 从网络上下载图片
     * @param urlString
     * @param outputStream
     * @return
     */
    private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
        HttpURLConnection urlConnection = null;
        BufferedOutputStream out = null;
        BufferedInputStream in = null;
        try {
            final URL url = new URL(urlString);
            urlConnection = (HttpURLConnection) url.openConnection();
            in = new BufferedInputStream(urlConnection.getInputStream(), 8 * 1024);
            out = new BufferedOutputStream(outputStream, 8 * 1024);
            int b;
            while ((b = in.read()) != -1) {
                out.write(b);
            }
            return true;
        } catch (final IOException e) {
            e.printStackTrace();
        } finally {
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            try {
                if (out != null) {
                    out.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (final IOException e) {
                e.printStackTrace();
            }
        }
        return false;
    }


    /***
     * 获取当前应用的版本号
     * @param context
     * @return
     */
    public int getAppVersion(Context context) {
        try {
            PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
            return info.versionCode;
        } catch (PackageManager.NameNotFoundException e) {
            e.printStackTrace();
        }
        return 1;
    }

    /**
     * 获取硬盘缓存的地址
     *
     * @param context
     * @param uniqueName
     * @return
     */
    public File getDiskCacheDir(Context context, String uniqueName) {
        String cachePath;
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())
                || !Environment.isExternalStorageRemovable()) {
            cachePath = context.getExternalCacheDir().getPath();
        } else {
            cachePath = context.getCacheDir().getPath();
        }
        return new File(cachePath + File.separator + uniqueName);
    }

}

主界面的调用方法，和内存缓存一样，这是一个demo，延迟几秒，然后从硬盘缓存中取图片 ,案例比较清晰易懂，基本一看都会懂

package image.reeman.com.imageloader;

import android.graphics.Bitmap;
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.File;

public class MainActivity extends AppCompatActivity {

    DiskCacheUtil lruCacheUtil;
    private ImageView iv_desc;

    private Handler handler = new Handler();

    @Override

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intView();
    }

    private void intView() {
        iv_desc = (ImageView) findViewById(R.id.iv_image);

        lruCacheUtil = new DiskCacheUtil(MainActivity.this);
        lruCacheUtil.saveBitmapToDisk();

        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                Bitmap map = lruCacheUtil.getBitmapFromDisk();
                if (map == null) {
                    Toast.makeText(MainActivity.this, "=====", Toast.LENGTH_SHORT).show();
                }
                iv_desc.setImageBitmap(map);
            }
        }, 5000);

    }
}