首先看缓存单元Entry 和 entry的管理器editor的定义：

Entry: 即缓存项， 可以有valueCount个 value， 每个value是一个文件，文件名是[key].[index] , index的值从0到 valueCount . 每个entry的 sequenceNumber、readable、 lengths等值会在被Editor编辑并commit之后有 DiskLruCache负责更新。

所谓 dirty file， 就是处在编辑状态的file。

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

Editor：编辑器，对entry进行编辑、更新、保存， 有点儿类似于 SharedPreferrence的 Editor。

/** 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;}}}public String getString(int index) throws IOException {InputStream in = newInputStream(index);return in != null ? inputStreamToString(in) : null;}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;}}}}