diff --git a/GDMS.iml b/GDMS.iml
index 4bde68d..4c713fc 100644
--- a/GDMS.iml
+++ b/GDMS.iml
@@ -29,6 +29,5 @@
         <SOURCES />
       </library>
     </orderEntry>
-    <orderEntry type="library" scope="PROVIDED" name="mariadb-java-client-2.3.0" level="project" />
   </component>
 </module>
\ No newline at end of file
diff --git a/src/dao/DBManagement.java b/src/dao/DBManagement.java
index e597616..d8718a4 100644
--- a/src/dao/DBManagement.java
+++ b/src/dao/DBManagement.java
@@ -1,10 +1,6 @@
 package dao;
 
-import java.sql.Connection;
-import java.sql.DriverManager;
-import java.sql.SQLException;
-import java.sql.Statement;
-import java.util.Properties;
+import java.sql.*;
 
 import org.apache.tomcat.jdbc.pool.DataSource;
 import org.apache.tomcat.jdbc.pool.PoolProperties;
@@ -19,20 +15,24 @@ public class DBManagement {
 
     public static DataSource dataSource = new DataSource();
 
-    public void init(){
+    private static boolean ifInit = false;
+
+    public static void init(){
         PoolProperties poolProperties = new PoolProperties();
         poolProperties.setUrl(url);
         poolProperties.setDriverClassName(driverClassName);
         poolProperties.setUsername(username);
         poolProperties.setPassword(password);
         dataSource.setPoolProperties(poolProperties);
-    }
-    public static Connection getConnection(){
         try {
             Class.forName(driverClassName);
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         }
+        ifInit = true;
+    }
+    public static Connection getConnection(){
+        if(!ifInit) return null;
         try {
             return DriverManager.getConnection(url,username,password);
         } catch (SQLException e) {
@@ -40,4 +40,45 @@ public class DBManagement {
         }
         return null;
     }
+
+    public static ResultSet query(String sql) {
+        if(!ifInit) return null;
+        ResultSet rs = null;
+        Connection con = null;
+        try{
+            con = DBManagement.getConnection();
+            Statement stmt = con.createStatement();
+            rs = stmt.executeQuery(sql);
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }finally {
+            if(con!=null) {
+                try {
+                    con.close();
+                } catch (SQLException e) {
+                    e.printStackTrace();
+                }
+            }
+        }
+        return rs;
+    }
+    public static void update(String sql) {
+        if(!ifInit) return;
+        Connection con = null;
+        try{
+            con = DBManagement.getConnection();
+            Statement stmt = con.createStatement();
+            stmt.executeUpdate(sql);
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }finally {
+            if(con!=null) {
+                try {
+                    con.close();
+                } catch (SQLException e) {
+                    e.printStackTrace();
+                }
+            }
+        }
+    }
 }
diff --git a/src/init/Init.java b/src/init/Init.java
index dfc60d4..3d42bad 100644
--- a/src/init/Init.java
+++ b/src/init/Init.java
@@ -13,7 +13,7 @@ import java.io.IOException;
 @WebServlet(name = "Init")
 public class Init extends HttpServlet {
     public void init(){
-        new DBManagement().init();
+        DBManagement.init();
         new test();
     }
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {