Enhance FileRefreshableDataSource and FileWritableDataSource (#125)

- Add method to check if the resource is modified in `AutoRefreshDataSource`
- Implement FileWritableDataSource

sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/AutoRefreshDataSource.java

@@ -25,8 +25,10 @@ import com.alibaba.csp.sentinel.log.RecordLog;
 /**
  * A {@link ReadableDataSource} automatically fetches the backend data.
  *
- * @param <S> source data type
- * @param <T> target data type
+ * @param <S>
+ *            source data type
+ * @param <T>
+ *            target data type
  * @author Carpenter Lee
  */
 public abstract class AutoRefreshDataSource<S, T> extends AbstractDataSource<S, T> {
@@ -50,13 +52,15 @@ public abstract class AutoRefreshDataSource<S, T> extends AbstractDataSource<S,
 
     private void startTimerService() {
         service = Executors.newScheduledThreadPool(1,
-            new NamedThreadFactory("sentinel-datasource-auto-refresh-task", true));
+                new NamedThreadFactory("sentinel-datasource-auto-refresh-task", true));
         service.scheduleAtFixedRate(new Runnable() {
             @Override
             public void run() {
                 try {
+                    if (!refresh()) {
+                        return;
+                    }
                     T newValue = loadConfig();
-
                     getProperty().updateValue(newValue);
                 } catch (Throwable e) {
                     RecordLog.info("loadConfig exception", e);
@@ -72,4 +76,8 @@ public abstract class AutoRefreshDataSource<S, T> extends AbstractDataSource<S,
             service = null;
         }
     }
+
+    protected boolean refresh() {
+        return true;
+    }
 }

sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java

@@ -25,11 +25,12 @@ import com.alibaba.csp.sentinel.log.RecordLog;
 
 /**
  * <p>
- * A {@link ReadableDataSource} based on file. This class will automatically fetches the backend file every refresh period.
+ * A {@link ReadableDataSource} based on file. This class will automatically
+ * fetches the backend file every refresh period.
  * </p>
  * <p>
- * Limitations: Default read buffer size is 1 MB. If file size is greater than buffer size, exceeding bytes will
- * be ignored. Default charset is UTF-8.
+ * Limitations: Default read buffer size is 1 MB. If file size is greater than
+ * buffer size, exceeding bytes will be ignored. Default charset is UTF-8.
  * </p>
  *
  * @author Carpenter Lee
@@ -45,35 +46,37 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
     private byte[] buf;
     private final Charset charset;
     private final File file;
+    private long lastModified = 0L;
 
     /**
-     * Create a file based {@link ReadableDataSource} whose read buffer size is 1MB, charset is UTF8,
-     * and read interval is 3 seconds.
+     * Create a file based {@link ReadableDataSource} whose read buffer size is
+     * 1MB, charset is UTF8, and read interval is 3 seconds.
      *
-     * @param file         the file to read
-     * @param configParser the config decoder (parser)
+     * @param file
+     *            the file to read
+     * @param configParser
+     *            the config decoder (parser)
      */
     public FileRefreshableDataSource(File file, Converter<String, T> configParser) throws FileNotFoundException {
         this(file, configParser, DEFAULT_REFRESH_MS, DEFAULT_BUF_SIZE, DEFAULT_CHAR_SET);
     }
 
-    public FileRefreshableDataSource(String fileName, Converter<String, T> configParser)
-        throws FileNotFoundException {
+    public FileRefreshableDataSource(String fileName, Converter<String, T> configParser) throws FileNotFoundException {
         this(new File(fileName), configParser, DEFAULT_REFRESH_MS, DEFAULT_BUF_SIZE, DEFAULT_CHAR_SET);
     }
 
     public FileRefreshableDataSource(File file, Converter<String, T> configParser, int bufSize)
-        throws FileNotFoundException {
+            throws FileNotFoundException {
         this(file, configParser, DEFAULT_REFRESH_MS, bufSize, DEFAULT_CHAR_SET);
     }
 
     public FileRefreshableDataSource(File file, Converter<String, T> configParser, Charset charset)
-        throws FileNotFoundException {
+            throws FileNotFoundException {
         this(file, configParser, DEFAULT_REFRESH_MS, DEFAULT_BUF_SIZE, charset);
     }
 
-    public FileRefreshableDataSource(File file, Converter<String, T> configParser, long recommendRefreshMs,
-                                     int bufSize, Charset charset) throws FileNotFoundException {
+    public FileRefreshableDataSource(File file, Converter<String, T> configParser, long recommendRefreshMs, int bufSize,
+            Charset charset) throws FileNotFoundException {
         super(configParser, recommendRefreshMs);
         if (bufSize <= 0 || bufSize > MAX_SIZE) {
             throw new IllegalArgumentException("bufSize must between (0, " + MAX_SIZE + "], but " + bufSize + " get");
@@ -87,6 +90,7 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
         this.buf = new byte[bufSize];
         this.file = file;
         this.charset = charset;
+        this.lastModified = file.lastModified();
         firstLoad();
     }
 
@@ -107,7 +111,7 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
             FileChannel channel = inputStream.getChannel();
             if (channel.size() > buf.length) {
                 throw new IllegalStateException(file.getAbsolutePath() + " file size=" + channel.size()
-                    + ", is bigger than bufSize=" + buf.length + ". Can't read");
+                        + ", is bigger than bufSize=" + buf.length + ". Can't read");
             }
             int len = inputStream.read(buf);
             return new String(buf, 0, len, charset);
@@ -121,6 +125,16 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
         }
     }
 
+    @Override
+    protected boolean refresh() {
+        long curLastModified = new File(file.getAbsolutePath()).lastModified();
+        if (curLastModified != this.lastModified) {
+            this.lastModified = curLastModified;
+            return true;
+        }
+        return false;
+    }
+
     @Override
     public void close() throws Exception {
         super.close();

sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileWritableDataSource.java

@@ -16,11 +16,13 @@
 package com.alibaba.csp.sentinel.datasource;
 
 import java.io.File;
+import java.io.FileOutputStream;
 
 /**
  * A {@link WritableDataSource} based on file.
  *
- * @param <T> data type
+ * @param <T>
+ *            data type
  * @author Eric Zhao
  * @since 0.2.0
  */
@@ -46,7 +48,27 @@ public class FileWritableDataSource<T> implements WritableDataSource<T> {
 
     @Override
     public void write(T value) throws Exception {
-        throw new UnsupportedOperationException("Not implemented");
+        if (configEncoder == null) {
+            throw new NullPointerException("configEncoder is null Can't write");
+        }
+        synchronized (file) {
+            String convertResult = configEncoder.convert(value);
+            FileOutputStream outputStream = null;
+            try {
+                outputStream = new FileOutputStream(file);
+                byte[] bytesArray = convertResult.getBytes();
+                outputStream.write(bytesArray);
+                outputStream.flush();
+            } finally {
+                if (outputStream != null) {
+                    try {
+                        outputStream.close();
+                    } catch (Exception ignore) {
+                        // nothing
+                    }
+                }
+            }
+        }
     }
 
     @Override