fix:持久化模块的小bug

add:持久化模块的新单元测试

src/main/java/minsecurity/identity/persist/sqlite/Sqlite.java

@@ -36,12 +36,16 @@ public class Sqlite {
 
     }
 
+    /**
+     * 将密码转换为16进制表示
+     * @return 16进制字符串 String
+     */
     private String passwd2HexKey(){
         return String.format("x'%s'", passwd);
     }
 
     /**
-     * 获取Sqlite object
+     * 获取Sqlite 实例
      * @return Sqlite object
      */
     public static Sqlite getInstance() {
@@ -90,10 +94,19 @@ public class Sqlite {
         }
     }
     //自定义文件地址,注意要用/结尾,比如:/min/identity/
+
+    /**
+     * 打开用户指定路径的数据库文件
+     * @param filePath String
+     * @throws Exception
+     */
     public void open(String filePath) throws Exception {
         Connection c = null;
         Statement stmt = null;
         try{
+            if (filePath == null || filePath.length() == 0){
+                throw new Exception("invalid db path!");
+            }
             db_path = filePath;
             boolean db_exists = SqliteUtil.pathExists(db_path);
             if (!db_exists){
@@ -114,6 +127,11 @@ public class Sqlite {
         }
     }
 
+    /**
+     * 从打开的数据库获取连接
+     * @return Connection
+     * @throws Exception
+     */
     public Connection getConn() throws Exception {
         Connection c = null;
         try{