diff --git a/app/src/main/java/io/legado/app/utils/Encoder.kt b/app/src/main/java/io/legado/app/utils/Encoder.kt
index b74266fa3..8f97c4c83 100644
--- a/app/src/main/java/io/legado/app/utils/Encoder.kt
+++ b/app/src/main/java/io/legado/app/utils/Encoder.kt
@@ -3,26 +3,20 @@ package io.legado.app.utils
 object Encoder {
 
     fun escape(src: String): String {
-        var i = 0
-        var char: Char
         val tmp = StringBuilder()
-        tmp.ensureCapacity(src.length * 6)
-        while (i < src.length) {
-            char = src[i]
-            if (Character.isDigit(char) || Character.isLowerCase(char)
-                || Character.isUpperCase(char)
-            )
+        for (char in src) {
+            val charCode = char.toInt()
+            if (charCode in 48..57 || charCode in 65..90 || charCode in 97..122) {
                 tmp.append(char)
-            else if (char.toInt() < 256) {
-                tmp.append("%")
-                if (char.toInt() < 16)
-                    tmp.append("0")
-                tmp.append(char.toInt().toString(16))
-            } else {
-                tmp.append("%u")
-                tmp.append(char.toInt().toString(16))
+                continue
             }
-            i++
+
+            val prefix = when {
+                charCode < 16 -> "%0"
+                charCode < 256 -> "%"
+                else -> "%u"
+            }
+            tmp.append(prefix).append(charCode.toString(16))
         }
         return tmp.toString()
     }
diff --git a/app/src/main/java/io/legado/app/utils/FileUtils.kt b/app/src/main/java/io/legado/app/utils/FileUtils.kt
index 8c5ba3823..e64869d11 100644
--- a/app/src/main/java/io/legado/app/utils/FileUtils.kt
+++ b/app/src/main/java/io/legado/app/utils/FileUtils.kt
@@ -21,20 +21,7 @@ object FileUtils {
     fun getSdPath() = Environment.getExternalStorageDirectory().absolutePath
 
     fun getFileByPath(filePath: String): File? {
-        return if (isSpace(filePath)) null else File(filePath)
-    }
-
-    fun isSpace(s: String?): Boolean {
-        if (s == null) return true
-        var i = 0
-        val len = s.length
-        while (i < len) {
-            if (!Character.isWhitespace(s[i])) {
-                return false
-            }
-            ++i
-        }
-        return true
+        return if (filePath.isBlank()) null else File(filePath)
     }
 
     fun getSdCardPath(): String {
@@ -101,12 +88,9 @@ object FileUtils {
         return paths
     }
 
-    @TargetApi(Build.VERSION_CODES.KITKAT)
     fun getPath(context: Context, uri: Uri): String? {
-        val isKitKat = Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT
-
         // DocumentProvider
-        if (isKitKat && DocumentsContract.isDocumentUri(context, uri)) {
+        if (DocumentsContract.isDocumentUri(context, uri)) {
             // ExternalStorageProvider
             if (isExternalStorageDocument(uri)) {
                 val docId = DocumentsContract.getDocumentId(uri)
@@ -119,7 +103,7 @@ object FileUtils {
 
             } else if (isDownloadsDocument(uri)) {
                 val id = DocumentsContract.getDocumentId(uri)
-                val split = id.split(":".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
+                val split = id.split(":").dropLastWhile { it.isEmpty() }.toTypedArray()
                 val type = split[0]
                 if ("raw".equals(
                         type,
diff --git a/app/src/main/java/io/legado/app/utils/NetworkUtils.kt b/app/src/main/java/io/legado/app/utils/NetworkUtils.kt
index 79ce84ef9..ae2d42d47 100644
--- a/app/src/main/java/io/legado/app/utils/NetworkUtils.kt
+++ b/app/src/main/java/io/legado/app/utils/NetworkUtils.kt
@@ -8,37 +8,18 @@ object NetworkUtils {
 
     private val notNeedEncoding: BitSet by lazy {
         val bitSet = BitSet(256)
-        var i: Int = 'a'.toInt()
-        while (i <= 'z'.toInt()) {
+        for (i in 'a'.toInt()..'z'.toInt()) {
             bitSet.set(i)
-            i++
         }
-        i = 'A'.toInt()
-        while (i <= 'Z'.toInt()) {
+        for (i in 'A'.toInt()..'Z'.toInt()) {
             bitSet.set(i)
-            i++
         }
-        i = '0'.toInt()
-        while (i <= '9'.toInt()) {
+        for (i in '0'.toInt()..'9'.toInt()) {
             bitSet.set(i)
-            i++
         }
-        bitSet.set('+'.toInt())
-        bitSet.set('-'.toInt())
-        bitSet.set('_'.toInt())
-        bitSet.set('.'.toInt())
-        bitSet.set('$'.toInt())
-        bitSet.set(':'.toInt())
-        bitSet.set('('.toInt())
-        bitSet.set(')'.toInt())
-        bitSet.set('!'.toInt())
-        bitSet.set('*'.toInt())
-        bitSet.set('@'.toInt())
-        bitSet.set('&'.toInt())
-        bitSet.set('#'.toInt())
-        bitSet.set(','.toInt())
-        bitSet.set('['.toInt())
-        bitSet.set(']'.toInt())
+        for (char in "+-_.$:()!*@&#,[]") {
+            bitSet.set(char.toInt())
+        }
         return@lazy bitSet
     }
 
@@ -69,7 +50,6 @@ object NetworkUtils {
             // 其他字符，肯定需要urlEncode
             needEncode = true
             break
-            i++
         }
 
         return !needEncode
@@ -79,7 +59,7 @@ object NetworkUtils {
      * 判断c是否是16进制的字符
      */
     private fun isDigit16Char(c: Char): Boolean {
-        return c >= '0' && c <= '9' || c >= 'A' && c <= 'F'
+        return c in '0'..'9' || c in 'A'..'F' || c in 'a'..'f'
     }
 
     /**
diff --git a/app/src/main/java/io/legado/app/utils/README.md b/app/src/main/java/io/legado/app/utils/README.md
deleted file mode 100644
index a31b943b5..000000000
--- a/app/src/main/java/io/legado/app/utils/README.md
+++ /dev/null
@@ -1 +0,0 @@
-## 放置一些工具类
\ No newline at end of file
diff --git a/app/src/main/java/io/legado/app/utils/StringExtensions.kt b/app/src/main/java/io/legado/app/utils/StringExtensions.kt
index 0ec34e16e..de179f1da 100644
--- a/app/src/main/java/io/legado/app/utils/StringExtensions.kt
+++ b/app/src/main/java/io/legado/app/utils/StringExtensions.kt
@@ -17,7 +17,7 @@ fun String?.isJson(): Boolean = this?.run {
 } ?: false
 
 fun String?.htmlFormat(): String = if (this.isNullOrBlank()) "" else
-    this.replace("(?i)<(br[\\s/]*|/*p.*?|/*div.*?)>".toRegex(), "\n")// 替换特定标签为换行符
+    this.replace("(?i)<(br[\\s/]*|/*p\\b.*?|/*div\\b.*?)>".toRegex(), "\n")// 替换特定标签为换行符
         .replace("<[script>]*.*?>|&nbsp;".toRegex(), "")// 删除script标签对和空格转义符
         .replace("\\s*\\n+\\s*".toRegex(), "\n　　")// 移除空行,并增加段前缩进2个汉字
         .replace("^[\\n\\s]+".toRegex(), "　　")//移除开头空行,并增加段前缩进2个汉字