I'm implementing MVC using JSP and JDBC. I have imported a database class file to my JSP file and I would like to show the data of a DB table. I don't know how I should return the ResultSet from the Java class to the JSP page and embed it in HTML.
How can I achieve this?
In a well designed MVC approach, the JSP file should not contain any line of Java code and the servlet class should not contain any line of JDBC code.
Assuming that you want to show a list of products in a webshop, the following code needs to be created.
A Product class representing a real world entity of a product, it should be just a Javabean.
public class Product {
private Long id;
private String name;
private String description;
private BigDecimal price;
// Add/generate getters/setters/c'tors/equals/hashcode boilerplate.
}
A DAO class which does all the nasty JDBC work and returns a nice List<Product>.
public class ProductDAO {
private DataSource dataSource;
public ProductDAO(DataSource dataSource) {
this.dataSource = dataSource;
}
public List<Product> list() throws SQLException {
List<Product> products = new ArrayList<Product>();
try (
Connection connection = dataSource.getConnection();
PreparedStatement statement = connection.prepareStatement("SELECT id, name, description, price FROM product");
ResultSet resultSet = statement.executeQuery();
) {
while (resultSet.next()) {
Product product = new Product();
product.setId(resultSet.getLong("id"));
product.setName(resultSet.getString("name"));
product.setDescription(resultSet.getString("description"));
product.setPrice(resultSet.getBigDecimal("price"));
products.add(product);
}
}
return products;
}
}
A servlet class which obtains the list and puts it in the request scope.
#WebServlet("/products")
public class ProductsServlet extends HttpServlet {
#Resource(name="jdbc/YourDB") // For Tomcat, define as <Resource> in context.xml and declare as <resource-ref> in web.xml.
private DataSource dataSource;
private ProductDAO productDAO;
#Override
public void init() {
productDAO = new ProductDAO(dataSource);
}
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
List<Product> products = productDAO.list();
request.setAttribute("products", products); // Will be available as ${products} in JSP
request.getRequestDispatcher("/WEB-INF/products.jsp").forward(request, response);
} catch (SQLException e) {
throw new ServletException("Cannot obtain products from DB", e);
}
}
}
Finally a JSP file in /WEB-INF/products.jsp which uses JSTL <c:forEach> to iterate over List<Product> which is made available in EL by ${products}, and uses JSTL <c:out> to escape string properties in order to avoid XSS holes when it concerns user-controlled input.
<%# taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%# taglib uri="http://java.sun.com/jsp/jstl/format" prefix="fmt" %>
...
<table>
<c:forEach items="${products}" var="product">
<tr>
<td>${product.id}</td>
<td><c:out value="${product.name}" /></td>
<td><c:out value="${product.description}" /></td>
<td><fmt:formatNumber value="${product.price}" type="currency" currencyCode="USD" /></td>
</tr>
</c:forEach>
</table>
To get it to work, just call the servlet by its URL. Provided that the servlet is annotated #WebServlet("/products") or mapped in web.xml with <url-pattern>/products</url-pattern>, then you can call it by http://example.com/contextname/products
See also:
How to avoid Java code in JSP files?
doGet and doPost in Servlets
How should I connect to JDBC database / datasource in a servlet based application?
Design Patterns web based applications
RequestDispatcher.forward() vs HttpServletResponse.sendRedirect()
How to map a ResultSet with unknown amount of columns to a List and display it in a HTML table?
How do I pass current item to Java method by clicking a hyperlink or button in JSP page?
MVC, in a web application context, doesn't consist in using a class from a JSP. It consists in using the following model :
browser sends a request to a web server
the web server is configured so that the request is handled by a servlet or a filter (the controller : Java code, not JSP code)
The servlet/filter usually dispatches the request to a specific class (called an Action, the specific part of the controller), based on configuration/annotations
The action executes the business logic (i.e. fetch the data from the database in your example : the model)
The action forwards the request to a JSP. The role of the JSP is only to generate HTML code (i.e. display your data : the view)
Since the JSP usually uses JSP tags (the JSTL, for example) and the JSP expression language, and since JSP tags and the EL are designed to get information from JavaBeans, you'd better have your data available in the form of JavaBeans or collections of JavaBeans.
The role of the controller (the action class) is thus to fetch the data, to create JavaBean instances containing the data, in a suitable format for the JSP, to put them in request attributes, and then to dispatch to the JSP. The JSP will then iterate through the JavaBean instances and display what they contain.
You should not implement the MVC framework yourself. Use existing ones (Stripes, Struts, etc.)
I don't know how should I return the ResultSet from the class file to the JSP page
Well, you don't.
The point of MVC is to separate your model ( the M DB info in this case ) from your view ( V a jsp, in this case ) in such a way you can change the view without braking to application.
To do this you might use an intermediate object to represent your data ( usually called DTO - after Data Transfer Object -, don't know how they call it these days ), and other object to fetch it ( usually a DAO ).
So basically you have your JSP file, get the request parameters, and then invoke a method from the DAO. The dao, internally has the means to connect to the db and fetch the data and builds a collections of DTO's which are returned to the JSP for rendering.
Something like this extremely simplified ( and insecure ) code:
Employee.java
class Employee {
String name;
int emplid;
}
EmployeeDAO.java
class EmployeeDAO {
... method to connect
etc.
List<Employee> getAllNamed( String name ) {
String query = "SELECT name, emplid FROM employee where name like ?";
ResultSet rs = preparedStatement.executeQuery etc etc.
List<Employee> results = ....
while( rs.hasNext() ) {
results.add( new Employee( rs.getString("name"), rs.getInt("emplid")));
}
// close resources etc
return results;
}
}
employee.jsp
<%
request.setAttribute("employees", dao.getAllNamed( request.getParameter("name") );
%>
<table>
<c:forEach items="${employees}" var="employee">
<tr><td>${employee.emplid}</td><td>${employee.name}</td></tr>
</c:forEach>
</table>
I hope this give you a better idea.
I have a problem. I don't understand clearly the code. I have a similar problem with my code.
I have created database SQL and filled up. Then I want to implement a MainServlet (code below) that richieve data from database and in a different jsp page, I want to insert that data in section like h1, h2 ecc... I must use the ${} sintax but I don't know how do that.
Briefly, In jsp file (code below, I MUST USE ${} SINTAX) I want to "call" MainServlet and there I want to richieve data from database and view in jsp file.
I hope I have explained correctly, thank you very much!
MainServlet.java
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class MainServlet
*/
#WebServlet({ "/MainServlet" })
public class MainServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final String PATH_JSP = "/WEB-INF/";
/**
* #see HttpServlet#HttpServlet()
*/
public MainServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* #see Servlet#init(ServletConfig)
*/
public void init(ServletConfig config) throws ServletException {
// TODO Auto-generated method stub
}
/**
* #see Servlet#destroy()
*/
public void destroy() {
// TODO Auto-generated method stub
}
/**
* #see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String doveAndare = request.getParameter("azione");
if(doveAndare==null)
doveAndare = "index";
try {
String driverString = "com.mysql.cj.jdbc.Driver";
Class.forName(driverString);
String connString = "jdbc:mysql://localhost:3306/ldd_jewels?user=root&password=";
Connection conn = DriverManager.getConnection(connString);
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM JEWEL");
while (rs.next() == true) {
System.out.println(rs.getString("Category") + "\t" + rs.getString("Name"));
/* I try that but does not work
request.setAttribute("name", rs.getString("Name"));
javax.servlet.RequestDispatcher dispatcher = request.getRequestDispatcher("/WEB-INF/widering_male.jsp");
dispatcher.forward(request, response); */
}
stmt.close();
conn.close();
} catch(Exception e) {
e.printStackTrace();
}
request.getRequestDispatcher(PATH_JSP+doveAndare+".jsp").forward(request, response);
}
/**
* #see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
doublerow.jsp
<section id="portfolio-details" class="portfolio-details">
<div class="container">
<div class="row gy-4">
<div class="col-lg-8">
<div class="portfolio-details-slider swiper">
<div class="swiper-wrapper align-items-center">
<div class="swiper-slide">
<img src="assets/img/jewels/doublerow_1.jpg" alt="" />
</div>
<div class="swiper-slide">
<img src="assets/img/jewels/doublerow_2.jpg" alt="" />
</div>
<div class="swiper-slide">
<img src="assets/img/jewels/doublerow_3.jpg" alt="" />
</div>
</div>
<div class="swiper-pagination"></div>
</div>
</div>
<div class="col-lg-4">
<div class="portfolio-info">
<h3>Product details</h3>
<ul>
<li><strong>Code</strong>: 1S3D5</li>
<li><strong>Category</strong>: Bracelets</li>
<li><strong>Name</strong>: Double Row Hinged Bangle</li>
<li><strong>Gender</strong>: Female</li>
<li><strong>Material</strong>: Yellow gold</li>
<li><strong>Size</strong>: 121mm</li>
<li><strong>Price</strong>: €5500</li>
</ul>
</div>
<div class="portfolio-description">
<h2>Description of product</h2>
<p>
The entwined ends of Tiffany Knot’s signature motif symbolize
the power of connections between people. Balancing strength
and elegance, each Tiffany Knot design is a complex feat of
craftsmanship. This bangle is crafted with yellow gold and
polished by hand for high shine. Wear on its own or partnered
with classic silhouettes for an unexpected pairing.
</p>
</div>
</div>
</div>
</div>
</section>
This is my database:
I want to insert each jewel in different pages (each jewel have a jsp file)
You can use the <c:forEach > tag
you can find a detailed example in the following link example use
I think it will be better for you to contain the data of the table into a collection such as list and return the list from the Java class and reuse this collection in the JSP.
Related
So, I have struggled for 2 days to understand what my error is. My drop down list is not populating with data from the database. I am using Java EE and MySQL.
I can insert data in the database without a problem but when i retrieve it for some reason the jsp doesn't do its thing correctly so that I always get the drop down empty.
This is the table I am using:
create table category(
category_id int auto_increment,
name varchar(30),
primary key(category_id)
);
This is the servlet I am using and the method for executing the query. As you can see I am returning a List of objects and then I am adding it as a request attribute in the doGet method. So I guess until here everything should work fine.
public class DropDownServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException {
try {
List<Category> categories = retrieveCategories();
request.setAttribute("categories", categories);
RequestDispatcher view = request.getRequestDispatcher("viewdropdown.jsp");
view.forward(request, response);
} catch (ClassNotFoundException | SQLException | IOException ex) {
ex.printStackTrace();
}
}
public static List<Category> retrieveCategories() throws ClassNotFoundException, SQLException {
Connection conn = DatabaseConnection.initializeConnection();
String query = "Select * from category";
PreparedStatement pstmnt = conn.prepareStatement(query);
List<Category> categories = new ArrayList<>();
ResultSet rs = pstmnt.executeQuery();
while (rs.next()) {
int id = rs.getInt("category_id");
String name = rs.getString("name");
Category cat = new Category(id,name);
categories.add(cat);
}
conn.close();
return categories;
}
and here is the jsp with the dropdown which doesn't display the data that it should.
<html>
<head>
<title>Dropdown page</title>
</head>
<body>
<h1>The names of the categories are the following:</h1>
<select id ="dropdown">
<c:forEach items="${categories}" var="category">
<option value = "${category.name}">${category.name}</option>
</c:forEach>
</select>
<br>
<br>
</body>
</html>
EDIT:
So I have created this hardcoded test method to test my code and I add it as request parameter identically to how I added the other method with the DB query. My DropDown is still empty, so the problem could be from the way I try to display the items in the jsp. I think it could be in the loop I have.
public static List<Category> testMethod(){
List<Category> list = new ArrayList<>();
Category one = new Category(1,"Blue");
Category two = new Category(2,"Red");
list.add(one);
list.add(two);
return list;
}
Looks like the ${categories} is an empty collection.
First, make sure, you have imported the JSTL Core library into your JSP page. This is done by putting
<%# taglib prefix="c" uri = "http://java.sun.com/jsp/jstl/core" %>
at the top of the JSP page.
Additionally, you can check on the JSP side if the collection is empty by adding somewhere:
<c:out value="${categories.size()}" />.
Also, you are using Expression Language directly between the HTML <option> tags, so you will also need adding:
<%# page isELIgnored = "false" %>
at the top of the JSP page to make it evaluable to the appropriate value, instead of rendering plain text.
I'm implementing MVC using JSP and JDBC. I have imported a database class file to my JSP file and I would like to show the data of a DB table. I don't know how I should return the ResultSet from the Java class to the JSP page and embed it in HTML.
How can I achieve this?
In a well designed MVC approach, the JSP file should not contain any line of Java code and the servlet class should not contain any line of JDBC code.
Assuming that you want to show a list of products in a webshop, the following code needs to be created.
A Product class representing a real world entity of a product, it should be just a Javabean.
public class Product {
private Long id;
private String name;
private String description;
private BigDecimal price;
// Add/generate getters/setters/c'tors/equals/hashcode boilerplate.
}
A DAO class which does all the nasty JDBC work and returns a nice List<Product>.
public class ProductDAO {
private DataSource dataSource;
public ProductDAO(DataSource dataSource) {
this.dataSource = dataSource;
}
public List<Product> list() throws SQLException {
List<Product> products = new ArrayList<Product>();
try (
Connection connection = dataSource.getConnection();
PreparedStatement statement = connection.prepareStatement("SELECT id, name, description, price FROM product");
ResultSet resultSet = statement.executeQuery();
) {
while (resultSet.next()) {
Product product = new Product();
product.setId(resultSet.getLong("id"));
product.setName(resultSet.getString("name"));
product.setDescription(resultSet.getString("description"));
product.setPrice(resultSet.getBigDecimal("price"));
products.add(product);
}
}
return products;
}
}
A servlet class which obtains the list and puts it in the request scope.
#WebServlet("/products")
public class ProductsServlet extends HttpServlet {
#Resource(name="jdbc/YourDB") // For Tomcat, define as <Resource> in context.xml and declare as <resource-ref> in web.xml.
private DataSource dataSource;
private ProductDAO productDAO;
#Override
public void init() {
productDAO = new ProductDAO(dataSource);
}
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
List<Product> products = productDAO.list();
request.setAttribute("products", products); // Will be available as ${products} in JSP
request.getRequestDispatcher("/WEB-INF/products.jsp").forward(request, response);
} catch (SQLException e) {
throw new ServletException("Cannot obtain products from DB", e);
}
}
}
Finally a JSP file in /WEB-INF/products.jsp which uses JSTL <c:forEach> to iterate over List<Product> which is made available in EL by ${products}, and uses JSTL <c:out> to escape string properties in order to avoid XSS holes when it concerns user-controlled input.
<%# taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%# taglib uri="http://java.sun.com/jsp/jstl/format" prefix="fmt" %>
...
<table>
<c:forEach items="${products}" var="product">
<tr>
<td>${product.id}</td>
<td><c:out value="${product.name}" /></td>
<td><c:out value="${product.description}" /></td>
<td><fmt:formatNumber value="${product.price}" type="currency" currencyCode="USD" /></td>
</tr>
</c:forEach>
</table>
To get it to work, just call the servlet by its URL. Provided that the servlet is annotated #WebServlet("/products") or mapped in web.xml with <url-pattern>/products</url-pattern>, then you can call it by http://example.com/contextname/products
See also:
How to avoid Java code in JSP files?
doGet and doPost in Servlets
How should I connect to JDBC database / datasource in a servlet based application?
Design Patterns web based applications
RequestDispatcher.forward() vs HttpServletResponse.sendRedirect()
How to map a ResultSet with unknown amount of columns to a List and display it in a HTML table?
How do I pass current item to Java method by clicking a hyperlink or button in JSP page?
MVC, in a web application context, doesn't consist in using a class from a JSP. It consists in using the following model :
browser sends a request to a web server
the web server is configured so that the request is handled by a servlet or a filter (the controller : Java code, not JSP code)
The servlet/filter usually dispatches the request to a specific class (called an Action, the specific part of the controller), based on configuration/annotations
The action executes the business logic (i.e. fetch the data from the database in your example : the model)
The action forwards the request to a JSP. The role of the JSP is only to generate HTML code (i.e. display your data : the view)
Since the JSP usually uses JSP tags (the JSTL, for example) and the JSP expression language, and since JSP tags and the EL are designed to get information from JavaBeans, you'd better have your data available in the form of JavaBeans or collections of JavaBeans.
The role of the controller (the action class) is thus to fetch the data, to create JavaBean instances containing the data, in a suitable format for the JSP, to put them in request attributes, and then to dispatch to the JSP. The JSP will then iterate through the JavaBean instances and display what they contain.
You should not implement the MVC framework yourself. Use existing ones (Stripes, Struts, etc.)
I don't know how should I return the ResultSet from the class file to the JSP page
Well, you don't.
The point of MVC is to separate your model ( the M DB info in this case ) from your view ( V a jsp, in this case ) in such a way you can change the view without braking to application.
To do this you might use an intermediate object to represent your data ( usually called DTO - after Data Transfer Object -, don't know how they call it these days ), and other object to fetch it ( usually a DAO ).
So basically you have your JSP file, get the request parameters, and then invoke a method from the DAO. The dao, internally has the means to connect to the db and fetch the data and builds a collections of DTO's which are returned to the JSP for rendering.
Something like this extremely simplified ( and insecure ) code:
Employee.java
class Employee {
String name;
int emplid;
}
EmployeeDAO.java
class EmployeeDAO {
... method to connect
etc.
List<Employee> getAllNamed( String name ) {
String query = "SELECT name, emplid FROM employee where name like ?";
ResultSet rs = preparedStatement.executeQuery etc etc.
List<Employee> results = ....
while( rs.hasNext() ) {
results.add( new Employee( rs.getString("name"), rs.getInt("emplid")));
}
// close resources etc
return results;
}
}
employee.jsp
<%
request.setAttribute("employees", dao.getAllNamed( request.getParameter("name") );
%>
<table>
<c:forEach items="${employees}" var="employee">
<tr><td>${employee.emplid}</td><td>${employee.name}</td></tr>
</c:forEach>
</table>
I hope this give you a better idea.
I have a problem. I don't understand clearly the code. I have a similar problem with my code.
I have created database SQL and filled up. Then I want to implement a MainServlet (code below) that richieve data from database and in a different jsp page, I want to insert that data in section like h1, h2 ecc... I must use the ${} sintax but I don't know how do that.
Briefly, In jsp file (code below, I MUST USE ${} SINTAX) I want to "call" MainServlet and there I want to richieve data from database and view in jsp file.
I hope I have explained correctly, thank you very much!
MainServlet.java
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class MainServlet
*/
#WebServlet({ "/MainServlet" })
public class MainServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final String PATH_JSP = "/WEB-INF/";
/**
* #see HttpServlet#HttpServlet()
*/
public MainServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* #see Servlet#init(ServletConfig)
*/
public void init(ServletConfig config) throws ServletException {
// TODO Auto-generated method stub
}
/**
* #see Servlet#destroy()
*/
public void destroy() {
// TODO Auto-generated method stub
}
/**
* #see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String doveAndare = request.getParameter("azione");
if(doveAndare==null)
doveAndare = "index";
try {
String driverString = "com.mysql.cj.jdbc.Driver";
Class.forName(driverString);
String connString = "jdbc:mysql://localhost:3306/ldd_jewels?user=root&password=";
Connection conn = DriverManager.getConnection(connString);
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM JEWEL");
while (rs.next() == true) {
System.out.println(rs.getString("Category") + "\t" + rs.getString("Name"));
/* I try that but does not work
request.setAttribute("name", rs.getString("Name"));
javax.servlet.RequestDispatcher dispatcher = request.getRequestDispatcher("/WEB-INF/widering_male.jsp");
dispatcher.forward(request, response); */
}
stmt.close();
conn.close();
} catch(Exception e) {
e.printStackTrace();
}
request.getRequestDispatcher(PATH_JSP+doveAndare+".jsp").forward(request, response);
}
/**
* #see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
doublerow.jsp
<section id="portfolio-details" class="portfolio-details">
<div class="container">
<div class="row gy-4">
<div class="col-lg-8">
<div class="portfolio-details-slider swiper">
<div class="swiper-wrapper align-items-center">
<div class="swiper-slide">
<img src="assets/img/jewels/doublerow_1.jpg" alt="" />
</div>
<div class="swiper-slide">
<img src="assets/img/jewels/doublerow_2.jpg" alt="" />
</div>
<div class="swiper-slide">
<img src="assets/img/jewels/doublerow_3.jpg" alt="" />
</div>
</div>
<div class="swiper-pagination"></div>
</div>
</div>
<div class="col-lg-4">
<div class="portfolio-info">
<h3>Product details</h3>
<ul>
<li><strong>Code</strong>: 1S3D5</li>
<li><strong>Category</strong>: Bracelets</li>
<li><strong>Name</strong>: Double Row Hinged Bangle</li>
<li><strong>Gender</strong>: Female</li>
<li><strong>Material</strong>: Yellow gold</li>
<li><strong>Size</strong>: 121mm</li>
<li><strong>Price</strong>: €5500</li>
</ul>
</div>
<div class="portfolio-description">
<h2>Description of product</h2>
<p>
The entwined ends of Tiffany Knot’s signature motif symbolize
the power of connections between people. Balancing strength
and elegance, each Tiffany Knot design is a complex feat of
craftsmanship. This bangle is crafted with yellow gold and
polished by hand for high shine. Wear on its own or partnered
with classic silhouettes for an unexpected pairing.
</p>
</div>
</div>
</div>
</div>
</section>
This is my database:
I want to insert each jewel in different pages (each jewel have a jsp file)
You can use the <c:forEach > tag
you can find a detailed example in the following link example use
I think it will be better for you to contain the data of the table into a collection such as list and return the list from the Java class and reuse this collection in the JSP.
I was trying to forward from doPost to doGet of the ControllerServlet urlPattern = "/remove_person", so I can re-update findAll query inside my doGet method of the ControllerServlet class, and then forward to remove_person.jsp from doGet method, but AS-WEB-CORE-00089 exception is thrown
WARNING: StandardWrapperValve[ControllerServlet]: Servlet.service() for servlet ControllerServlet threw exception
javax.servlet.ServletException: AS-WEB-CORE-00089
at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:863)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:739)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:575)
at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:546)
at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:428)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:378)
at server.ControllerServlet.doPost(ControllerServlet.java:130)
where ControllerServlet.java:130 line is in doPost() method:
request.getRequestDispatcher(url).forward(request, response);
Here is the code of servlet class:
#WebServlet(
name = "ControllerServlet",
loadOnStartup = 1,
urlPatterns = {
"/index",
"/search_person",
"/add_person",
"/remove_person"})
public class ControllerServlet extends HttpServlet {
#PersistenceUnit
private EntityManagerFactory emf;
#Resource
private UserTransaction utx;
private EntityManager em;
#Override
public void init() throws ServletException {
assert emf != null;
em = emf.createEntityManager();
}
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String servletPath = request.getServletPath();
if (servletPath.equals("/index")) {
}
else if (servletPath.equals("/search_person")) {
List persons = em.createNamedQuery("Person.findAll").getResultList();
request.setAttribute("findByNameAndYearBirth", persons);
}
else if (servletPath.equals("/add_person")) {
}
else if (servletPath.equals("/remove_person")) {
List persons = em.createNamedQuery("Person.findAll").getResultList();
request.setAttribute("findAll", persons);
}
String url = servletPath + ".jsp";
request.getRequestDispatcher(url).forward(request, response);
}
#Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String servletPath = request.getServletPath();
if (servletPath.equals("/index")) {
}
else if (servletPath.equals("/search_person")) {
String name = request.getParameter("name");
String yearBirth = request.getParameter("yearBirth");
Query query = em.createNamedQuery("Person.findAll");
if (!name.isEmpty() && !yearBirth.isEmpty()) {
query = em.createNamedQuery("Person.findByNameAndYearBirth");
query.setParameter("name", name);
query.setParameter("yearBirth", Short.parseShort(yearBirth));
}
else if (!name.isEmpty()) {
query = em.createNamedQuery("Person.findByModel");
query.setParameter("name", name);
}
else if (!yearBirth.isEmpty()) {
try {
Short sYearBirth = Short.parseShort(yearBirth);
query = em.createNamedQuery("Person.findByYearBirth");
query.setParameter("yearBirth", sYearBirth);
} catch (NumberFormatException nfe) {}
}
List persons = query.getResultList();
request.setAttribute("findByNameAndYearBirth", persons);
}
else if (servletPath.equals("/add_person")) {
String name = request.getParameter("name");
String hobby = request.getParameter("hobby");
String yearBirth = request.getParameter("yearBirth");
int personsLen = em.createNamedQuery("Person.findAll").getResultList().size();
Person newPerson = new Person(
++personsLen, name, hobby, Short.parseShort(yearBirth)
);
try {
utx.begin();
em = emf.createEntityManager();
em.persist(newPerson);
utx.commit();
} catch (Exception e) {
e.printStackTrace();
}
}
else if (servletPath.equals("/remove_person")) {
String id = request.getParameter("id");
Person person = null;
try {
utx.begin();
person = em.find(Person.class, Integer.parseInt(id));
em.remove(person);
utx.commit();
} catch (Exception e) {
e.printStackTrace();
}
servletPath = "/remove_person";
}
String url = servletPath;
request.getRequestDispatcher(url).forward(request, response);
}
}
Problem is, my line inside doPost method
String url = path;
does not contain a ".jsp" part.
But if I add ".jsp" part to a string url, then how I will update findAll query data inside remove_person.jsp if i don't go to servlet doGet first to collect new data after adding or deleting entities?
remove_person.jsp
<%#taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%#page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<h1>Remove Person</h1>
<form action="remove_person" method="post">
<table border="3">
<tr>
<th>ID</th>
<th>Name</th>
</tr>
<c:forEach var="person" begin="0" items="${findAll}">
<tr>
<td>${person.id}</td>
<td>${person.name}</td>
</tr>
</c:forEach>
</table>
<strong>Remove person: </strong>
<select name="id">
<c:forEach var="person" items="${findAll}">
<option value="${person.id}">${person.id}. ${person.name} </option>
</c:forEach>
</select>
<input type="submit" id="remove_person" value="Remove" />
</form>
<br>
Home page
</body>
</html>
Actually, is it even possible to forward from doPost to doGet method of the same servlet ? The reason I was trying to do this is because, inside doGet I already use this code:
List persons = em.createNamedQuery("Person.findAll").getResultList();
request.setAttribute("findAll", persons);
So why should I duplicate this code inside doPost method, when I can forward from doPost to doGet method and invoke that code?
UPDATE:
Bad approach:
String url = servletPath;
request.getRequestDispatcher(url).forward(request, response);
Correct approach:
String url = request.getContextPath() + servletPath;
response.sendRedirect(url);
Use redirect instead of forward. The pattern (called Post/Redirect/Get) is:
1) the client calls the post url, which does your update
2) the servlet sends a redirect to the client with the url for the get.
3) the client calls the url from the redirect.
When the response from the GET comes back the browser has the GET url, so the browser ends up with a url that's bookmarkable. Also this way the user can't repost the same data by hitting f5 or clicking multiple times.
For when to use forward vs redirect see this advice:
Forward
a forward is performed internally by the servlet
the browser is completely unaware that it has taken place, so its original URL remains intact
any browser reload of the resulting page will simple repeat the original request, with the original URL
Redirect
a redirect is a two step process, where the web application instructs the browser to fetch a second URL, which differs from the
original
a browser reload of the second URL will not repeat the original request, but will rather fetch the second URL
redirect is marginally slower than a forward, since it requires two browser requests, not one
objects placed in the original request scope are not available to the second request
In general, a forward should be used if the operation can be safely repeated upon a browser reload of the resulting web page; otherwise, redirect must be used. Typically, if the operation performs an edit on the datastore, then a redirect, not a forward, is required. This is simply to avoid the possibility of inadvertently duplicating an edit to the database.
I have a jsp page containing a form where a user fills in some value. Now i pass these values into a servlet which processes it and retieves a related set of data. Now, i am able to retrieve the data in the servlet page, but am not able to display it on the same jsp page at which i fetched the request.
I do not want to use java code inside jsp. I wish to do the same using servlets only. I do not want to do something like this
<% if(rollno==null)
// then display the form
else
// process the request on the jsp page itself
%>
I want to process all my reults in a servlet file and then dispaly the result on the jsp page by passing data from servlet to jsp. I am posting my code below :
<form id="form" method="post" action="searchServlet">
Student Roll No :<br><input type="text" value="" name="rollno"><br><br>
<input type="submit" value="SHOW DETAILS" />
</form>
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
try {
String rollno=request.getParameter("rollno");
ResultSet rs=null;
Class.forName("com.mysql.jdbc.Driver");
String url="jdbc:mysql://localhost/schooldatabase";
Connection con = DriverManager.getConnection(url,"root","passwd");
Statement st= (Statement) con.createStatement();
String strquery="SELECT name,regno FROM `schooldatabase`.`student_info` WHERE rollno="+ rollno+ ";";
if(!con.isClosed()) {
rs=st.executeQuery(strquery);
while(rs.next())
{
out.println(rs.getString("name"));
out.println(rs.getString("regno"));
}
}
else
{ // The connection is closed
}
}
catch(Exception e)
{
out.println(e);
}
finally {
out.close();
}
}
You shouldn't be doing the presentation in the servlet. You should not have any of those lines in the servlet.
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
// ...
out.println(rs.getString("name"));
out.println(rs.getString("regno"));
// ...
out.println(e);
You should instead be storing the data in a sensible collection and be setting it as a request attribute and finally forward the request/response to a JSP which in turn generates the proper HTML around all those data. Something like this:
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
List<Student> students = studentDAO.find(request.getParameter("rollno"));
request.setAttribute("students", students); // Will be available as ${students} in JSP
request.getRequestDispatcher("/WEB-INF/students.jsp").forward(request, response);
} catch (SQLException e) {
throw new ServletException("Cannot obtain students from DB", e);
}
}
with this in the students.jsp
<%# taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
...
<table>
<c:forEach items="${students}" var="student">
<tr>
<td>${student.name}</td>
<td>${student.regno}</td>
</tr>
</c:forEach>
</table>
For a more concrete example, see also this answer: Show JDBC ResultSet in HTML in JSP page using MVC and DAO pattern
See also:
Our Servlets wiki page - Contains several Hello World examples
I try to fetch values from servlet into my JSP, but it throws a NullPointerException or some other error.
This is the servlet which gets values from JSP:
buildingprofilerequest.java
package asset.management.arms.buildingprofilemodule;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.sun.xml.internal.ws.client.SenderException;
/**
* Servlet implementation class buildingprofilerequest
*/
public class buildingprofilerequest extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* #see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try{
buildingservice building = new buildingservice();
building.setBuilding_name(request.getParameter("combobox"));
building = BuildingDAO.build(building);
request.setAttribute("abcd", building);
RequestDispatcher dispatcher =
getServletContext().getRequestDispatcher("/building_profile_details.jsp");
dispatcher.include(request, response);
}
catch (Throwable theException)
{
System.out.println(theException);
}
}
My bean looks in brief like this:
buildingservice.java
package asset.management.arms.buildingprofilemodule;
public class buildingservice {
private String building_name;
public String getBuilding_name() {
return building_name;
}
public void setBuilding_name(String newbuilding_name) {
this.building_name = newbuilding_name;
}
//and has many more parameters and there getters and setters
}
My other class is BuildingDAO.java, here all the calculations are done:
package asset.management.arms.buildingprofilemodule;
import java.sql.*;
import asset.management.arms.loginmodule.ConnectionManager;
public class BuildingDAO {
static Connection currentCon = null;
static ResultSet rs = null;
public static buildingservice build(buildingservice bean) {
String building_name = bean.getBuilding_name();
String searchQuery = "select * from buildings";
try{
//connect to DB
currentCon = ConnectionManager.getConnection();
stmt=currentCon.createStatement();
rs = stmt.executeQuery(searchQuery);
while(rs.next()){
//retreiving building parameters from database
String buildingname = rs.getString("building_name");
String buildingnumber = rs.getString("building_number");
int buildarea = rs.getInt("build_area");
//setting building parameters
bean.setBuilding_name(buildingname);
bean.setBuilding_number(buildingnumber);
bean.setBuild_area(buildarea);
bean.setBuilt_year(builtyear);
catch (Exception ex)
{
System.out.println(" " + ex);
}
finally
{
if (rs != null) {
try {
rs.close();
} catch (Exception e) {}
rs = null;
}
if (stmt != null) {
try {
stmt.close();
} catch (Exception e) {}
stmt = null;
}
if (currentCon != null) {
try {
currentCon.close();
} catch (Exception e) {
}
currentCon = null;
}
}
return bean;
}
}
My JSP is this:
building_profile_details.jsp
<%# page language="java" contentType="text/html; charset=iso-8859-1"
pageEncoding="ISO-8859-1" import="asset.management.arms.buildingprofilemodule.buildingservice"%>
<% buildingservice hello = (buildingservice) request.getAttribute("abcd"); %>
<table width="1150" height="176" border="1" align="center" bordercolor="lightslategray">
<tr>
<td width="107"><div align="center"><b>Building Number</b> </div></td>
<td width="325"><div align="center"><b>Building Name </b></div></td>
<td width="70"><div align="center"><b>area</b></div></td>
<td width="146"><div align="center"><b>built year</b></div></td>
</tr>
<tr>
<td><div align="center"><%=hello.getBuilding_number()%></div></td>
<td><div align="center"><%= hello.getBuilding_name()%></div></td>
<td><div align="center"><%=hello.getBuild_area()%></div></td>
<td><div align="center"><%= hello.getBuilt_year()%></div></td>
</tr>
</table>
In the JSP I even tried other ways like:
<jsp:useBean id="hello" class="asset.management.arms.buildingprofilemodule.buildingservice">
and then in individual blocks of table:
<jsp:getProperty name="hello" name="building_name">
But nothing works, it throws error which says
org.apache.jasper.JasperException: Exception in JSP: /building_profile_details.jsp:82
82: <td><div align="center"><%=hello.getBuilding_number()%></div></td>
and similarly for other lines.
How is this caused and how can I solve this?
In your servlet, replace
dispatcher.include(request, response);
by
dispatcher.forward(request, response);
In your JSP, remove
<% buildingservice hello = (buildingservice) request.getAttribute("abcd"); %>
and replace
<td><div align="center"><%=hello.getBuilding_number()%></div></td>
<td><div align="center"><%= hello.getBuilding_name()%></div></td>
<td><div align="center"><%=hello.getBuild_area()%></div></td>
<td><div align="center"><%= hello.getBuilt_year()%></div></td>
by
<td><div align="center">${abcd.building_number}</div></td>
<td><div align="center">${abcd.building_name}</div></td>
<td><div align="center">${abcd.build_area}</div></td>
<td><div align="center">${abcd.built_year}</div></td>
See also:
Our Servlets wiki page
Our JSP wiki page
Our EL wiki page
There are by the way many other serious problems in your code, but they are not related to the current concrete problem. I'll however try to sum the most important ones up:
Code holds DB resources as static variables. This is a major threadsafety problem!
Code does not handle exceptions in a sensible manner. This is not developer nor user friendly.
Code does not respect Java naming conventions. This leads to developer confusion and maintainability problems.
Code (particularly the buildingservice and BuildingDAO) uses very odd approaches/patterns/flows. It look like to be written by a procedural programmer who doesn't understand Object Oriented Programming concepts.
JSP uses scriptlets which is discouraged since 2003. Keep yourself up to date. Java code belongs in Java classes and JSP should only contain HTML, JSP tags and EL.
HTML uses deprecated attributes. Keep yourself up to date. Learn CSS.
Work on that as well.