给js引擎增加java.utf8ToGbk编码转换

app/src/main/java/io/legado/app/help/JsExtensions.kt

@@ -52,4 +52,10 @@ interface JsExtensions {
     fun timeFormat(time: Long): String {
         return dateFormat.format(Date(time))
     }
+    //utf8编码转gbk编码
+    fun utf8ToGbk(str: String): String {
+        val utf8 = String(str.toByteArray(charset("UTF-8")))
+        val unicode = String(utf8.toByteArray(), charset("UTF-8"))
+        return String(unicode.toByteArray(charset("GBK")))
+    }
 }