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Hi im trying to get some table values from mysql database to playframework cli . For this i am using a Controller ,and one class to create the data connections. The first method is used to create the connection while the next one is used to execute the queries . However when i try to execute them it gives me a null pointer exception. I did read some other questions that were somewhat close to this but the issue is i am using play frameworks with an angular front end. Making adding the connector a little confusing . I did add it multiple times but it ust doesnt recognize it. I created a new java file and copy pasted the exact same code to another class and ran it using a main method andit works. the table name and the field names match each other. Any form of help is greatly appreciated.

Controller class:

public class HomeController extends Controller {

    public Result addBooks() {
        System.out.println(request().body().asText());
        JsonNode jsonNode = Json.toJson(new AppSummary("Book Added Successfully"));
        JsonNode json = Json.parse(request().body().asText());

        connect newcon = new connect();
        newcon.connection();
        newcon.checkBooks();

        return ok(jsonNode).as("application/json");
    }
}

The connection class with the jdbc connection and one query to execute

package controllers.librarycontrollers;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;


public class connect {
    private Connection conn;
    private Statement stmt;
    private ResultSet rstst;

    public void connection() {

        try {
            System.out.println("connected ");
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/librarymanager", "root", "");
            stmt = conn.createStatement();

        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }

    public void checkBooks() {
        try {
            String query = "select * from book";
            rstst = stmt.executeQuery(query);
            System.out.println("records added successfully");
            while (rstst.next()) {
                String title = rstst.getString("booktitle");
                String name = rstst.getString("authorName");

                System.out.println("booktitle:" + title + "authorName:" + name);
            }
            conn.close();
        } catch (Exception c) {
            System.out.println(c);
            System.out.println("not connected");
        }
    }
}

I am getting a null pointer exception and also the "not connected" print.

Anjula Serasinghe
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  • Where did you get `NullPointerException`? provide please more information – Ulad Dec 07 '18 at 23:50
  • connected,com.mysql.jdbc.Driver , java.lang.NullPointerException, not connected , this is what i get in the console. So im assuming the first "Connected" print is for the "connection" – Anjula Serasinghe Dec 07 '18 at 23:53
  • can you say in which line of code it happend? you should be able to see it in stack trace – Ulad Dec 07 '18 at 23:55
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    It is giving you a `NullPointerException` because you ignore the error that `com.mysql.jdbc.Driver` cannot be found on the classpath. **Do not catch exceptions and continue as-if nothing went wrong.** Fix your classpath, i.e. add the MySQL JDBC driver jar file. Depending on the JDBC driver version, you may also be specifying the wrong class name. Suggest to remove the `Class.forName()` call, since that should happen automatically if the jar file is in the classpath. – Andreas Dec 08 '18 at 00:06
  • Please post the full exception stacktrace (use `e.printStackTrace()` instead of `System.out.println(e.getMessage())`). – Mark Rotteveel Dec 08 '18 at 07:01

1 Answers1

1

Do you have references to mysql connector jar package in your Java application project? If not, loader is unable to find a class and then Null pointer exception can emerge.

VitezslavSimon
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