diff --git a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/FlowRuleManager.java b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/FlowRuleManager.java
index e0dac47a..f09701ae 100755
--- a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/FlowRuleManager.java
+++ b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/FlowRuleManager.java
@@ -110,6 +110,9 @@ public class FlowRuleManager {
         }
 
         for (FlowRule rule : list) {
+            if (!isValid(rule)) {
+                continue;
+            }
             if (StringUtil.isBlank(rule.getLimitApp())) {
                 rule.setLimitApp(FlowRule.LIMIT_APP_DEFAULT);
             }
@@ -199,4 +202,7 @@ public class FlowRuleManager {
 
     }
 
+    private static boolean isValid(FlowRule rule) {
+        return rule != null && !StringUtil.isBlank(rule.getResource());
+    }
 }
diff --git a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/AutoRefreshDataSource.java b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/AutoRefreshDataSource.java
index cca5fa6e..f2a8ab3e 100755
--- a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/AutoRefreshDataSource.java
+++ b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/AutoRefreshDataSource.java
@@ -25,10 +25,8 @@ 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> {
@@ -52,12 +50,12 @@ 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()) {
+                    if (!isModified()) {
                         return;
                     }
                     T newValue = loadConfig();
@@ -77,7 +75,7 @@ public abstract class AutoRefreshDataSource<S, T> extends AbstractDataSource<S,
         }
     }
 
-    protected boolean refresh() {
+    protected boolean isModified() {
         return true;
     }
 }
diff --git a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java
index 5f8249d6..43290611 100755
--- a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java
+++ b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java
@@ -26,7 +26,7 @@ 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.
+ * fetches the backend file every isModified period.
  * </p>
  * <p>
  * Limitations: Default read buffer size is 1 MB. If file size is greater than
@@ -46,16 +46,15 @@ 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.
      *
-     * @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);
@@ -66,23 +65,23 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
     }
 
     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 {
+                                     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");
         }
-        if (file == null) {
-            throw new IllegalArgumentException("file can't be null");
+        if (file == null || file.isDirectory()) {
+            throw new IllegalArgumentException("File can't be null or a directory");
         }
         if (charset == null) {
             throw new IllegalArgumentException("charset can't be null");
@@ -90,6 +89,7 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
         this.buf = new byte[bufSize];
         this.file = file;
         this.charset = charset;
+        // If the file does not exist, the last modified will be 0.
         this.lastModified = file.lastModified();
         firstLoad();
     }
@@ -105,13 +105,17 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
 
     @Override
     public String readSource() throws Exception {
+        if (!file.exists()) {
+            // Will throw FileNotFoundException later.
+            RecordLog.warn(String.format("[FileRefreshableDataSource] File does not exist: %s", file.getAbsolutePath()));
+        }
         FileInputStream inputStream = null;
         try {
             inputStream = new FileInputStream(file);
             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);
@@ -126,8 +130,8 @@ public class FileRefreshableDataSource<T> extends AutoRefreshDataSource<String,
     }
 
     @Override
-    protected boolean refresh() {
-        long curLastModified = new File(file.getAbsolutePath()).lastModified();
+    protected boolean isModified() {
+        long curLastModified = file.lastModified();
         if (curLastModified != this.lastModified) {
             this.lastModified = curLastModified;
             return true;
diff --git a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileWritableDataSource.java b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileWritableDataSource.java
index f6c41bbd..963a4345 100644
--- a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileWritableDataSource.java
+++ b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileWritableDataSource.java
@@ -17,46 +17,63 @@ package com.alibaba.csp.sentinel.datasource;
 
 import java.io.File;
 import java.io.FileOutputStream;
+import java.nio.charset.Charset;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+import com.alibaba.csp.sentinel.log.RecordLog;
 
 /**
  * A {@link WritableDataSource} based on file.
  *
- * @param <T>
- *            data type
+ * @param <T> data type
  * @author Eric Zhao
  * @since 0.2.0
  */
 public class FileWritableDataSource<T> implements WritableDataSource<T> {
 
+    private static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
+
     private final Converter<T, String> configEncoder;
-    private File file;
+    private final File file;
+    private final Charset charset;
+
+    private final Lock lock = new ReentrantLock(true);
 
     public FileWritableDataSource(String filePath, Converter<T, String> configEncoder) {
         this(new File(filePath), configEncoder);
     }
 
     public FileWritableDataSource(File file, Converter<T, String> configEncoder) {
+        this(file, configEncoder, DEFAULT_CHARSET);
+    }
+
+    public FileWritableDataSource(File file, Converter<T, String> configEncoder, Charset charset) {
         if (file == null || file.isDirectory()) {
             throw new IllegalArgumentException("Bad file");
         }
         if (configEncoder == null) {
             throw new IllegalArgumentException("Config encoder cannot be null");
         }
+        if (charset == null) {
+            throw new IllegalArgumentException("Charset cannot be null");
+        }
         this.configEncoder = configEncoder;
         this.file = file;
+        this.charset = charset;
     }
 
     @Override
     public void write(T value) throws Exception {
-        if (configEncoder == null) {
-            throw new NullPointerException("configEncoder is null Can't write");
-        }
-        synchronized (file) {
+        lock.lock();
+        try {
             String convertResult = configEncoder.convert(value);
             FileOutputStream outputStream = null;
             try {
                 outputStream = new FileOutputStream(file);
-                byte[] bytesArray = convertResult.getBytes();
+                byte[] bytesArray = convertResult.getBytes(charset);
+
+                RecordLog.info(String.format("[FileWritableDataSource] Writing to file %s: %s", file.toString(), convertResult));
                 outputStream.write(bytesArray);
                 outputStream.flush();
             } finally {
@@ -68,6 +85,8 @@ public class FileWritableDataSource<T> implements WritableDataSource<T> {
                     }
                 }
             }
+        } finally {
+            lock.unlock();
         }
     }