CustomModel.java

import javax.inject.Inject;
import javax.inject.Named;
import javax.jcr.Session;

import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.resource.Resource;
import org.apache.sling.api.resource.ResourceResolver;
import org.apache.sling.models.annotations.Default;
import org.apache.sling.models.annotations.DefaultInjectionStrategy;
import org.apache.sling.models.annotations.Model;
import org.apache.sling.models.annotations.injectorspecific.SlingObject;

/**
 * 
 * @author Yogesh Upadhyay
 * 
 */
@Model(adaptables = { SlingHttpServletRequest.class, Resource.class }, defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)
public class CustomModel {

  // If the field or method name doesn't exactly match the property name, @Named
  // can be used:
  @Inject
  @Named("author")
  private String authorPath;

  // Can use default value
  @Inject
  @Default(values = "")
  private String bodyText;

  // Can inject Custom Sling Object which exactly match sling object name
  // http://adobe-consulting-services.github.io/acs-aem-commons/features/aem-sling-models-injectors.html
  @SlingObject
  private Resource currentResource;

  // Can inject custom Object
  @Inject
  private ResourceResolver resourceResolver;
  
  //Inject a custom osgi service all available injector https://sling.apache.org/documentation/bundles/models.html#available-injectors
   @Inject @Source("osgi-services") 
   private YourService yourService;

  // This will return author property from current resource
  // same as properties.get("author") from jsp
  public String getAuthorPath() {
    return this.authorPath;
  }

  // return body text property
  public String getBodytext() {
    return this.bodyText;
  }

  // Example of how you can use sling Injector
  public String getResourcePath() {
    return currentResource.getPath();
  }

  // Example of how you can use custom injector
  public Session getSession() {
    return this.resourceResolver.adaptTo(Session.class);
  }

  // There are many other cool things you can do with sling model.
  // more example http://sling.apache.org/documentation/bundles/models.html

}

defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL is giving a compilation error i am using org.apache.sling.models 1.2.0

@rammohany yes, it is deprecated in Model 1.2.0. You can ignore that.