Sling Servlets

In Sling, Servlets can be registered as OSGi services like below:

   1. The @SlingServlet annotation
@SlingServlet(
resourceTypes = "sling/servlet/default",
selectors = "hello",
extensions = "html",
methods = "GET")
public class MyServlet extends SlingSafeMethodsServlet {
//TO DO
}

2. The @Properties and @Property annotations
@Component(metatype = true)
@Service(Servlet.class)
@Properties({
@Property(name = "sling.servlet.resourceTypes", value = "sling/servlet/default"),

@Property(name = "sling.servlet.selectors", value = "hello"),
@Property(name = "sling.servlet.extensions", value = "html"),
@Property(name = "sling.servlet.methods", value = "GET")
})
public class MyServlet extends SlingSafeMethodsServlet {
@Override
protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response)
throws ServletException, IOException {
//TO DO
}
}

3. Registering the servlet by path
@SlingServlet(
paths={"/bin/customservlet/hashim"}
)
@Properties({

@Property(name="service.pid", value="com.day.servlets.SampleServlet",propertyPrivate=false),
@Property(name="service.description",value="SampleDescription", propertyPrivate=false),
@Property(name="service.vendor",value="SampleVendor", propertyPrivate=false)
})
public class SampleServlet extends SlingAllMethodsServlet
{
@Override
protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response)
throws ServletException, IOException
{
//TO DO
}
@Override
protected void doPost(SlingHttpServletRequest request, SlingHttpServletResponse response)
throws ServletException, IOException
{
//TO DO
}
}
4. Register servlet by Resource Type
@SlingServlet(
resourceTypes = {"rep:User"},
methods = {"GET", "POST"}
)

@Properties({
@Property(name="service.pid", value="com.day.servlets.SampleServlet",propertyPrivate=false),
@Property(name="service.description",value="SampleDescription", propertyPrivate=false),
@Property(name="service.vendor",value="SampleVendor", propertyPrivate=false)
})
public class SampleServlet extends SlingAllMethodsServlet
{
@Override
protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response)
throws ServletException, IOException
{
//TO DO
}
@Override
protected void doPost(SlingHttpServletRequest request, SlingHttpServletResponse response)
throws ServletException, IOException
{
//TO DO
}
}

Note:  If you want your @SlingServlet to fetch some properties from Felix Console Configurations using @Properties , add the parameter “metatype=true” in the form of declaration where @SlingServlet is used. 
This parameter is responsible for a Service component to be available in Felix Console configMgr. 
why resourceType is much more prefered for writing SlingServlets. Below are the reasons:
  1. While defining a path , you must be specific what all paths are allowed to be used in the ServletResource OSGi service. If you define something randomly, your servlet might not be fucntional. Only a limited paths are allowed and the rest are blocked unless you open them up. This is resolved using resourceType.
  2. You may have also configure the dispatcher , if you use some random path for your servlet. This might be a potential security threat and a needless configuration.
  3. You might also have to specify the paths to your consumers for your servlet and any change in that path could have a serious affect. This might not be the case when you use resourceType