Question

我的问题与[Link]非常相似：（Why Servlet.service() for servlet [XYZ] in context with path [/ABC] threw exception）但我认为它没有得到解决。

这是一个简单的SQL网关应用程序，在我的个人计算机localhost上运行正常。但是，当我将war文件上传到服务器时，它会抛出此异常

org.apache.catalina.core.StandardWrapperValve invoke SEVERE: Servlet.service() for servlet [SqlGatewayServlet] in context with path [/DEV-JDBC] threw exception java.lang.NullPointerException at sql.SqlGatewayServlet.do

java.lang.NullPointerException sql.SqlGatewayServlet.doPost(SqlGatewayServlet.java:34)

行：34是Statement statement = connection.createStatement();

SqlGatewayServlet

public class SqlGatewayServlet extends HttpServlet {

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    String sqlStatement = request.getParameter("sqlStatement");
    String sqlResult = "";



    try{
        ConnectionPool pool = ConnectionPool.getInstance();
        Connection connection = pool.getConnection();

        // create a statement
        Statement statement = connection.createStatement();

        // parse the SQL string
        sqlStatement = sqlStatement.trim();
        if(sqlStatement.length() > 6){

            String sqlType = sqlStatement.substring(0, 6);
            if(sqlType.equalsIgnoreCase("select")){

                // create the HTML for the result set
                ResultSet resultSet = statement.executeQuery(sqlStatement);
                sqlResult = SQLUtil.getHtmlTable(resultSet);
                resultSet.close();

            }else{

                int i = statement.executeUpdate(sqlStatement);
                // a DDL statement
                if(i == 0){
                    sqlResult = "The statement executed successfully";
                }else{
                    sqlResult = "The statment executed sucessfully.<br>"
                            + i + "row(s) affected.";
                }                   
            }
        statement.close();
        connection.close();

        }

    }catch( SQLException e){
        sqlResult = "Error executing the SQL statement: <br>"
                + e.getMessage();

    }
    HttpSession session = request.getSession();
    session.setAttribute("sqlResult", sqlResult);
    session.setAttribute("sqlStatement", sqlStatement);

    String url = "/index.jsp";

    RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);

    dispatcher.forward(request, response);
}

}

context.xml中

<Context path="/DEV-JDBC">

<Resource name="jdbc/uplink_project" auth="Container" 
    maxActive="100" maxIdle="30" maxWait="10000" 
    username="xxxxx" password="xxxxxx" 
    driverClassName="com.mysql.jdbc.Driver" 
    url="jdbc:mysql://localhost:2082/uplink_project?autoReconnect=true" 
    logAbandoned="true" removeAbandoned="true" 
    removeAbandonedTimeout="60" type="javax.sql.DataSource" />

我的设置有问题吗？或者它的服务器问题？请告诉我您需要的其他信息。

提前感谢

Answer 1

问题出在方法ConnectionPool上getConnection()，因为connection是null。

Answer 2

如果以下语句中存在空指针异常：

   Statement statement = connection.createStatement();

然后它表示您的连接对象为空。

从ConnectionPool类初始化连接对象时。因此，请确保其getConnection方法返回有效的连接对象：

    ConnectionPool pool = ConnectionPool.getInstance();
    Connection connection = pool.getConnection();

您需要调试ConnectionPool类。

严重：Servlet [SqlGatewayServlet]的Servlet.service（）在路径[/ DEV-JDBC]的上下文中引发了异常

2 个答案: