How do I define a servlet with @WebServlet annotation?

Annotations is one new feature introduces in the Servlet 3.0 Specification. Previously to declare servlets, listeners or filters we must do it in the web.xml file. Now, with the new annotations feature we can just annotate servlet classes using the @WebServlet annotation.

package org.kodejava.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

        name = "HelloAnnotationServlet",
        urlPatterns = {"/hello", "/helloanno"},
        asyncSupported = false,
        initParams = {
                @WebInitParam(name = "name", value = "admin"),
                @WebInitParam(name = "param1", value = "value1"),
                @WebInitParam(name = "param2", value = "value2")
public class HelloAnnotationServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        PrintWriter out = response.getWriter();
        out.write("<html><head><title>WebServlet Annotation</title></head>");
        out.write("<h1>Servlet Hello Annotation</h1>");
        out.write("Welcome " + getServletConfig().getInitParameter("name"));

After you’ve deploy the servlet you’ll be able to access it either using the /hello or /helloanno url.

The table below give brief information about the attributes accepted by the @WebServlet annotation and their purposes.

name The servlet name, this attribute is optional.
description The servlet description and it is an optional attribute.
displayName The servlet display name, this attribute is optional.
urlPatterns An array of url patterns use for accessing the servlet, this attribute is required and should at least register one url pattern.
asyncSupported Specifies whether the servlet supports asynchronous processing or not, the value can be true or false.
initParams An array of @WebInitParam, that can be used to pass servlet configuration parameters. This attribute is optional.
loadOnStartup An integer value that indicates servlet initialization order, this attribute is optional.
smallIcon A small icon image for the servlet, this attribute is optional.
largeIcon A large icon image for the servlet, this attribute is optional.

Maven dependencies


Maven Central

How do I use @Select annotation in MyBatis?

In the previous example How do I create MyBatis mapper? you’ve seen how to use a mapper to get a record from the database. In that example the select query is defined in the mapper xml file. For the same functionality MyBatis also offer a solution to use an annotation for the select query.

In this example we will use the @Select annotation to define the query. To map the query result we can use the @ResultMap annotation where the value passed to this annotation is the result map id that we’ve defined in the mapper xml file.

Let see an example of a mapper interface definition that use an annotation to get a record from database:

package org.kodejava.mybatis;

import org.apache.ibatis.annotations.ResultMap;
import org.apache.ibatis.annotations.Select;

public interface RecordMapper {
     * Get a single Record from the database based on the record
     * identified.
     * @param id record identifier.
     * @return a record object.
    @Select("SELECT * FROM records WHERE id = #{id}")
    Record getRecord(int id);

Maven Dependencies


Maven Central Maven Central

How do I get all annotations?

To obtains all annotations for classes, methods, constructors, or fields we use the getAnnotations()method. This method returns an array of Annotation

In the following example we tried to read all annotations from the sayHi() method. First we need to obtain the method object itself. Because the sayHi() method has parameters, we need to pass not only the method name to the getMethod() method, but we also need to pass the parameter’s type.

The getAnnotations() method returns only annotation that has a RetentionPolicy.RUNTIME, because other retention policy doesn’t allow the annotation to available at runtime.

package org.kodejava.lang.annotation;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

public class GetAllAnnotation {
    private final Map<String, String> data = new HashMap<>();

    public static void main(String[] args) {
        GetAllAnnotation demo = new GetAllAnnotation();
        demo.sayHi("001", "Alice");
        demo.sayHi("004", "Malory");

        try {
            Class<? extends GetAllAnnotation> clazz = demo.getClass();

            // To get the sayHi() method we need to pass not only the method
            // name but also its parameters type so the getMethod() method
            // return the correct method for us to use.
            Method method = clazz.getMethod("sayHi", String.class, String.class);

            // Get all annotations from the sayHi() method. But this actually
            // will only return one annotation. Because only the HelloAnnotation
            // annotation that has RUNTIME retention policy, which means that
            // the other annotations associated with sayHi() method is not
            // available at runtime.
            Annotation[] annotations = method.getAnnotations();
            for (Annotation annotation : annotations) {
                System.out.println("Type: " + annotation.annotationType());
        } catch (NoSuchMethodException e) {

    @HelloAnnotation(value = "Hello", greetTo = "Everyone")
    public void sayHi(String dataId, String name) {
        Map<String, String> data = getData();
        if (data.containsKey(dataId)) {
            System.out.println("Hello " + data.get(dataId));
        } else {
            data.put(dataId, name);

    private Map<String, String> getData() {
        data.put("001", "Alice");
        data.put("002", "Bob");
        data.put("003", "Carol");
        return data;
package org.kodejava.lang.annotation;

public @interface MyAnnotation {
    String value();

Check the HelloAnnotation on the following link How do I create a simple annotation?.

The result of this code snippet:

Hello Alice
Type: interface org.kodejava.lang.annotation.HelloAnnotation

How do I obtain annotations at runtime using reflection?

This example demonstrate how to obtain annotations of a class and methods. We use the reflection API to get class and method information from where we can read information about annotation attached to the class or the method.

package org.kodejava.lang.annotation;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;

@HelloAnnotation(value = "Hello", greetTo = "Universe")
public class GettingAnnotation {
    public static void main(String[] args) {
        GettingAnnotation demo = new GettingAnnotation();

        Class<? extends GettingAnnotation> clazz = demo.getClass();
        Annotation[] annotations = clazz.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println("Annotation Type: " + annotation.annotationType());

        HelloAnnotation annotation = clazz.getAnnotation(HelloAnnotation.class);
        System.out.println("Value  : " + annotation.value());
        System.out.println("GreetTo: " + annotation.greetTo());

        try {
            Method m = clazz.getMethod("sayHi");

            annotation = m.getAnnotation(HelloAnnotation.class);
            System.out.println("Value  : " + annotation.value());
            System.out.println("GreetTo: " + annotation.greetTo());
        } catch (NoSuchMethodException e) {


    @HelloAnnotation(value = "Hi", greetTo = "Alice")
    public void sayHi() {

    @HelloAnnotation(value = "Hello", greetTo = "Bob")
    public void sayHello() {
        try {
            Method method = getClass().getMethod("sayHello");
            HelloAnnotation annotation = method.getAnnotation(HelloAnnotation.class);

            System.out.println(annotation.value() + " " + annotation.greetTo());
        } catch (NoSuchMethodException e) {

You can find the HelloAnnotation annotation that we use above on the following example: How do I create a simple annotation?.

The result of our program is:

Annotation Type: interface org.kodejava.lang.annotation.HelloAnnotation
Value  : Hello
GreetTo: Universe
Value  : Hi
GreetTo: Alice
Hello Bob

How do I annotate a class or method?

This example show you how to use the HelloAnnotation annotation on the previous example code, How do I create a simple annotation?. We add the HelloAnnotation annotation to our class and its methods.

package org.kodejava.lang.annotation;

@HelloAnnotation(value = "Good Morning", greetTo = "Universe")
public class HelloAnnotationExample {
    public static void main(String[] args) {
        HelloAnnotationExample hello = new HelloAnnotationExample();

    @HelloAnnotation(value = "Hi there", greetTo = "Alice")
    private void sayHi() {

    @HelloAnnotation(value = "Hello there", greetTo = "Bob")
    private void sayHello() {