Question

This is a simple program where i create two tables in a database using jdbc and sql.

Connection con=null;
try
{
Class.forName("com.mysql.jdbc.Driver");
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/","root","root");
try
{
Statement st=con.createStatement();
st.executeUpdate("CREATE DATABASE IF NOT EXISTS ARCPAGE");
st.executeUpdate("USE ARCPAGE");
st.executeUpdate("CREATE TABLE IF NOT EXISTS User(user_id integer NOT NULL AUTO_INCREMENT,user_name varchar(20) NOT NULL,user_pass varchar(20) NOT NULL,PRIMARY KEY (user_id))");
st.executeUpdate("CREATE TABLE IF NOT EXISTS Usermap(user_name varchar(20) NOT NULL,role_name varchar(20) NOT NULL)");
ResultSet res=st.executeQuery("SELECT * FROM USER");
res.next();
ResultSet resmap=st.executeQuery("SELECT * FROM USERMAP WHERE USER_NAME='"+res.getString("user_name")+"'");
/*error line */ res.next();
resmap=st.executeQuery("SELECT * FROM USERMAP WHERE USER_NAME='"+res.getString("user_name")+"'");
}
catch(SQLException e)
{
    System.out.println("SQL ERROR");
}
}
catch(Exception e)
{
    System.out.println("ERROR");
}

on executing the code i get an “SQL ERROR” from the catch block.on further investigation i see that the error is from the /error line/ which i marked. what am i doing wrong???

-krishan

on e.printstacktrace()

java.sql.SQLException: Operation not allowed after ResultSet closed
    at com.mysql.jdbc.ResultSet.checkClosed(ResultSet.java:652)
    at com.mysql.jdbc.ResultSet.next(ResultSet.java:5942)
    at trees.TreeBean.<init>(TreeBean.java:51)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:184)
    at com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:98)
    at com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:405)
    at com.sun.faces.mgbean.BeanManager.create(BeanManager.java:265)
    at com.sun.faces.el.ManagedBeanELResolver.resolveBean(ManagedBeanELResolver.java:191)
    at com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:73)
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:54)
    at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:71)
    at org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:69)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:112)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:106)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:190)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:178)
    at javax.faces.component.UIOutput.getValue(UIOutput.java:164)
    at org.primefaces.util.ComponentUtils.getStringValueToRender(ComponentUtils.java:61)
    at org.primefaces.component.inputtext.InputTextRenderer.encodeMarkup(InputTextRenderer.java:86)
    at org.primefaces.component.inputtext.InputTextRenderer.encodeEnd(InputTextRenderer.java:53)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:879)
    at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:308)
    at com.sun.faces.renderkit.html_basic.GridRenderer.renderRow(GridRenderer.java:181)
    at com.sun.faces.renderkit.html_basic.GridRenderer.encodeChildren(GridRenderer.java:125)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:849)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1643)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:164)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:849)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1643)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1646)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1646)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1646)
    at org.primefaces.component.tabview.TabViewRenderer.encodeContents(TabViewRenderer.java:180)
    at org.primefaces.component.tabview.TabViewRenderer.encodeMarkup(TabViewRenderer.java:120)
    at org.primefaces.component.tabview.TabViewRenderer.encodeEnd(TabViewRenderer.java:61)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:879)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1650)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1646)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1646)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:389)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:127)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:117)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:135)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:309)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Unknown Source)

Answer 1

Lots of stuff wrong with this code:

1. Prefer PreparedStatement to Statement.
2. Don’t create SQL by concatenating Strings; bind variables with “?”
3. You don’t close any of your Connection, Statement, or ResultSet assets.
4. Print the stack trace in catch blocks. Your message is no information at all.
5. You look like you want to JOIN results from User and UserMap, but this is an inefficient (n+1) query way to do it. Better to do a JOIN.
6. Shouldn’t you create tables in one method and query in another?

I don’t understand wny you have statements to create the database every time and create those tables. Shouldn’t that be done before you run these Java methods? Your code isn’t making much sense to me.

I’d write it more like this. I didn’t test it, but it does compile.

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.LinkedHashMap;
import java.util.Map;


public class SqlDemo {

    private static final String SELECT_USER_ROLE_SQL =
            "SELECT m.user_name, m.user_role " +
            "FROM User as u " +
            "JOIN Usermap as m" +
            "ON u.user_name = m.user_name ";

    public Map<String, String> getAllUserRoles(Connection connection) {
        Map<String, String> userRoles = new LinkedHashMap<String, String>();

        PreparedStatement ps = null;
        ResultSet rs = null;

        try {
            ps = connection.prepareStatement(SELECT_USER_ROLE_SQL);
            rs = ps.executeQuery();
            while (rs.next()) {
                String user = rs.getString("user_name");
                String role = rs.getString("user_role");
                userRoles.put(user, role);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        finally {
            close(rs);
            close(ps);
        }

        return userRoles;
    }

    private static void close(ResultSet rs) {
        try {
            if (rs != null) rs.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void close(Statement st) {
        try {
            if (st != null) st.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}