目前我正在製作一個應用程序,它是一個汽車租賃應用程序。該應用程序可以租一輛車,返回汽車等。爲了返回一輛汽車,我使用返回汽車的人的用戶名,嘗試查詢數據庫並取出他們租用的汽車,然後更新用戶以不再租用汽車並更新汽車詳細信息成爲可用。但是,我注意到,當我查詢數據庫我得到一個空回報。我看到我的桌子上有這個用戶,所以也許我的語法錯了,請幫忙。在我的sql一個servlet中查詢和更新2個單獨的表
protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
String carid = "";
String uname = req.getParameter("User_Name");
String defaulted = "User has no car";
int rs;
Connection conn = null;
java.sql.PreparedStatement st = null;
String nativeSQL = "";
ResultSet result =null;
try {
Context ctx = new InitialContext();
Context env = (Context) ctx.lookup("java:comp/env");
DataSource ds = (DataSource) env.lookup("jdbc/carRentalSystem");
conn = ds.getConnection();
conn.setAutoCommit(false);
result = st.executeQuery("SELECT * FROM userdetails where User_Name='"+ uname+"'");
if(result.next()) {
carid= result.getString("Car_Rental");
}
st = conn.prepareStatement("update userdetails SET Car_Rental ='" + defaulted+ "' where User_Name='" + uname+ "' ");
st.clearParameters();
rs = st.executeUpdate();
st = conn.prepareStatement("update cardetails SET Availability = 'Available' where id='" + carid+ "'");
st.clearParameters();
rs = st.executeUpdate();
if (rs != 0) {
res.sendRedirect("carRental.jsp");
return;
} else {
}
conn.commit();
} catch (Exception e) {
try{conn.rollback();}catch(Exception e1){}
e.printStackTrace();
} finally {
try {
if (st != null)
st.close();
} catch (java.sql.SQLException e) {
}
try {
if (conn != null)
conn.close();
} catch (java.sql.SQLException e) {
}
}
}
}
我的錯誤讀取,在使用javax在com.rental.servlet.AdminReturnCarServlet.doPost(AdminReturnCarServlet.java:63) 如下
INFO: Server startup in 7620 ms
顯示java.lang.NullPointerException .servlet.http.HttpServlet.service(HttpServlet.java:648) at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) at org.apache.catalina.core.ApplicationFilt erChain.internalDoFilter(ApplicationFilterChain.java:292) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java: 52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) at org.apache.catalina。 core.StandardWrapperValve.invoke(StandardWrapperValve.java:212) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java: 504) at org.apache.catalina.valves.AbstractAccessLogValve.i nvoke(AbstractAccessLogValve.java:620) 在org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) 在org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) 在org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter。服務(CoyoteAdapter.java:502) 在org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132) 在org.apache.coyote.AbstractProtocol $ AbstractConnectionHandler.process(AbstractProtocol.java:684) 在org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1539) at org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.run(NioEndpoint.java:1495) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent。 ThreadPoolExecutor $ Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java: 748)
我在通過調試模式運行時遇到了一些問題,但是如果無法登錄,我收到了一個錯誤,但是我無法登錄。說明無效的密碼 –
'uname'的價值是什麼?這是否與數據庫中的User_Name列完全匹配?在其他數據庫客戶端運行查詢時會發生什麼?另外,請參閱[SQL注入](https://www.owasp.org/index.php/SQL_Injection)攻擊。 –
uname的值是由客戶端給出的用戶名,它完全匹配User_Name列的用戶名。並感謝您的閱讀! –