Recommand · June 7, 2021 0

Servlet fails to update and returns a blank page

Am pretty new to programming in general and I have encountered a certain problem in my Java web app where my product information is not updating despite the adding and deleting of a product from the MySQL database working. When I hit submit on the update page the program would simply return me a blank page and the values would not update in the MySQL database.

Netbeans log and Apache tomcat logs are not returning error so I can only think that the redirection is going to a blank non-existing page instead but I have tried adding "../" to the form action but it did not work.

HTML form code:

<form method="post" action="product.update">
  <div class="row gtr-uniform">
    <!-- hidden form -->
    <input type="hidden" name="id" value="${product.getID()}">
    <div class="col-6 col-12-xsmall">
      <input type="text" id="name" placeholder="Product name" value="${product.getName()}" required />
    </div>

    <div class="col-6 col-12-xsmall">
      <input type="text" id="quantity" placeholder="Available quantity" value="${product.getProductQuantity()}" required />
    </div>
    <div class="col-6 col-12-xsmall">
      <input type="text" id="price" placeholder="Product price" value="${product.getPrice()}" required />
    </div>

    <!-- Break -->
    <div class="col-12">
      <ul class="actions">
        <li><input type="submit" value="Submit Form" class="primary" /></li>
      </ul>
    </div>
  </div>
</form>

Update product Servlet:

        response.setContentType("text/html;charset=UTF-8");
        String str_id=request.getParameter("id");
        String name=request.getParameter("name");
        String str_price=request.getParameter("price");
        String str_quantity=request.getParameter("quantity");
        
        ArrayList<String> errormsg=new ArrayList<>();
        boolean success=true;
        
        if(str_id==null || name==null || str_price==null || str_quantity==null){
            errormsg.add("Error: Null parameters.");
            success=false;
        }
        
        else if(str_id.isEmpty() || name.isEmpty() || str_price.isEmpty() || str_quantity.isEmpty()){
            errormsg.add("Error: Empty parameters.");
            success=false;
        }
        
        else{
            try{
                int id=Integer.parseInt(str_id);
                
                ProductDAO func=new ProductDAO();
                ProductBean bean=func.getProductByID(id);

                Double price=Double.parseDouble(str_price);
                int quantity=Integer.parseInt(str_quantity);
                
                success=func.updatePrice(bean, price) && func.updateName(bean, name) && func.updateStock(bean, quantity);
            }
            catch(NumberFormatException e){
                success=false;
                errormsg.add("Error: IDs are not integers.");
            }
            
            RequestDispatcher rd=request.getRequestDispatcher("WEB-INF/product/productupdate_success.jsp");
            if(success==false){
                rd=request.getRequestDispatcher("WEB-INF/errors/error.jsp");
                request.setAttribute("error", errormsg);
            }
            
            rd.forward(request, response);
        }

Product Bean class:

public class ProductBean implements java.io.Serializable{
    private int id;
    private Double price;
    private String name;
    private int quantity;
    
    public ProductBean(){
        this.id=-1;
        this.price=0.0;
        this.name="empty_noitem";
        this.quantity=0;
    }
    
    public ProductBean(int id, double prc, String nm, int qty){
        this.id=id;
        this.price=prc;
        this.name=nm;
        this.quantity=qty;
    }
    
    // setters
    public void updateID(int id){
        this.id=id;
    }
    
    public void updatePrice(double prc){
        this.price=prc;
    }
    
    public void updateName(String nm){
        this.name=nm;
    }
    
    public void updateProductQuantity(int qty){
        this.quantity=qty;
    }
    
    // getters
    public int getID(){
        return this.id;
    }
    
    public double getPrice(){
        return this.price;
    }
    
    public String getName(){
        return this.name;
    }
    
    public int getProductQuantity(){
        return this.quantity;
    }
}

Product DAO class:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.ResourceBundle;

/**
 *
 * @author SpicyAsh
 */
public class ProductDAO implements java.io.Serializable{
    private String driver;
    private String url;
    private String user;
    private String pass;
   
    private boolean loadClass(){
        try{
            Class.forName(driver);
        }catch (ClassNotFoundException e){
            e.printStackTrace();
            return false;
        }
        return true;
    }
    
    public void loadSQL(){
        ResourceBundle sql=ResourceBundle.getBundle("system.sql.sql");
        this.url=sql.getString("url");
        this.user=sql.getString("user");
        this.pass=sql.getString("password");
        this.driver=sql.getString("driver");
    }  
    
    public ProductDAO(String driver, String url, String user, String pass)
    {
        this.url=url;
        this.user=user;
        this.pass=pass;
        this.driver=driver;
    }
    
    public ProductDAO()
    {
        loadSQL();
    }
    
    public boolean exists(ProductBean bean){
        if(getProductByID(bean.getID())!=null || getProductByName(bean.getName())!=null){
            return true;
        }
        // else
        return false;
    }
    
    public boolean addProduct(ProductBean bean){
        loadClass();
        String sql="insert into product(product_name, price, quantity) values(?,?,?)";
        boolean success=true;
        
        // writing try-catch like this automatically closes the resources
        // this is called try-with-resources
        try(Connection conn=DriverManager.getConnection(url,user,pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            
            conn.setAutoCommit(false);
            ps.setString(1, bean.getName());
            ps.setDouble(2, bean.getPrice());
            ps.setInt(3, bean.getProductQuantity());
            
            ps.executeUpdate();
            
            conn.commit();
        }
        
        catch(SQLException e){
            success=false;
        }
        return success;
    }
    
    
    public ProductBean getProductByID(int inid){
        loadClass();
        String sql="select * from product where ID=?";
        ProductBean prod=new ProductBean();
        try(Connection conn=DriverManager.getConnection(url, user, pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            
            ps.setInt(1, inid);
            ResultSet rs=ps.executeQuery();
            
            while(rs.next()){                
                int id=rs.getInt("ID");
                String name=rs.getString("product_name");
                double price=rs.getDouble("price");
                int quantity=rs.getInt("quantity");
                prod.updateID(id);
                prod.updateName(name);
                prod.updatePrice(price);
                prod.updateProductQuantity(quantity);
            }
        }
        catch(SQLException e){
            e.printStackTrace();
        }
        
        return prod;
    }
    
    public ProductBean getProductByName(String inname){
        loadClass();
        String sql="select * from product where product_name=?";
        ProductBean prod=new ProductBean();
        try(Connection conn=DriverManager.getConnection(url, user, pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            
            ps.setString(1, inname);
            ResultSet rs=ps.executeQuery();
            
            while(rs.next()){
                int id=rs.getInt("ID");
                String name=rs.getString("product_name");
                double price=rs.getDouble("price");
                int quantity=rs.getInt("quantity");
                prod.updateID(id);
                prod.updateName(name);
                prod.updatePrice(price);
                prod.updateProductQuantity(quantity);
            }
        }
        catch(SQLException e){
            e.printStackTrace();
        }
        
        return prod;
    }
    
    public ArrayList<ProductBean> getAllProducts(){
        loadClass();
        String sql="select * from product";
        ProductBean bean=new ProductBean();
        ArrayList <ProductBean> arrList=new ArrayList<ProductBean>();
        try(Connection conn=DriverManager.getConnection(url, user, pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            
            ResultSet rs=ps.executeQuery();
            while(rs.next()){
                bean=new ProductBean();
                
                int id=rs.getInt("ID");
                String name=rs.getString("product_name");
                double price=rs.getDouble("price");
                int quantity=rs.getInt("quantity");
                bean.updateID(id);
                bean.updateName(name);
                bean.updatePrice(price);
                bean.updateProductQuantity(quantity);
                
                arrList.add(bean);
            }
        }
        catch(SQLException e){
            e.printStackTrace();
        }
        
        return arrList;
    }
    
    // update methods
    public boolean updatePrice(ProductBean row, Double newPrice){
        if(!exists(row)){
            return false;
        }

        loadClass();
        boolean success=true;    
        String sql="update product set price=? where id=?";

        try(Connection conn=DriverManager.getConnection(url,user,pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            conn.setAutoCommit(false);

            ps.setDouble(1, newPrice);
            ps.setInt(2, row.getID());
            ps.executeUpdate();
            conn.commit();
        }

        catch(SQLException e){
            success=false;
            e.printStackTrace();
        }
        return success;
    }
    
    // update methods
    public boolean updateName(ProductBean row, String newName){
        if(!exists(row)){
            return false;
        }

        loadClass();
        boolean success=true;
        String sql="update product set product_name=? where id=?";

        try(Connection conn=DriverManager.getConnection(url,user,pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            conn.setAutoCommit(false);

            ps.setString(1, newName);
            ps.setInt(2, row.getID());
            ps.executeUpdate();
            conn.commit();
        }

        catch(SQLException e){
            success=false;
            e.printStackTrace();
        }
        return success;
    }
    
    public boolean updateStock(ProductBean row, int newStock){
        if(!exists(row)){
            return false;
        }

        loadClass();
        boolean success=true;    
        String sql="update product set quantity=? where id=?";

        try(Connection conn=DriverManager.getConnection(url,user,pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            conn.setAutoCommit(false);

            ps.setInt(1, newStock);
            ps.setInt(2, row.getID());
            ps.executeUpdate();
            conn.commit();
        }

        catch(SQLException e){
            success=false;
            e.printStackTrace();
        }
        return success;
    }
    
    // delete method (ONLY ADMIN/OWNDER)
    public boolean removeProduct(ProductBean row){
        if(!exists(row)){
            return false;
        }
        
        loadClass();
        boolean success=true;
        String sql="delete from product where id=?";
        
        try(Connection conn=DriverManager.getConnection(url, user, pass);
                PreparedStatement ps=conn.prepareStatement(sql);){
            conn.setAutoCommit(false);
            ps.setInt(1,row.getID());
            ps.executeUpdate();
            conn.commit();
        }
        
        catch(SQLException e){
            success=false;
            e.printStackTrace();           
        }
        return success;
    }
}

Product table structure in MySQL:

Field Type Null Key Default Extra
id int NO PRI NULL auto_increment
product_name varchar(50) YES NULL
price double YES NULL
quantity int YES 0