Improve "Error handling" section

Author: decebals

_posts/2015-03-27-error-handling.md

@@ -13,7 +13,6 @@ Otherwise ErrorHandler will fallback to itself to handle the exception.
 By default each Application instance comes with a [DefaultErrorHandler]({{ site.coreurl }}/src/main/java/ro/pippo/core/DefaultErrorHandler.java) 
 that integrates with the `TemplateEngine` & `ContentTypeEngine`. It generates a representation of an exception or error result.  
 
-
 See below an custom ErrorHandler in action:
 ```java
 public class BasicApplication extends Application {
@@ -54,4 +53,75 @@ public class BasicApplication extends Application {
 }
 ```
 
-If you want to customize the template content for the default error templates (see the list of templates names in [TemplateEngine]({{ site.coreurl }}/src/main/java/ro/pippo/core/TemplateEngine.java)) then create a template with the same name in `src/main/resources/templates` folder. 
+If you want to customize the template content for the default error templates (see the list of templates names in [TemplateEngine]({{ site.coreurl }}/src/main/java/ro/pippo/core/TemplateEngine.java)) then create a template with the same name in `src/main/resources/templates` folder.
+ 
+So, by default, the following templates are available (copy/paste from `TemplateEngine.java`): 
+
+```java
+public final static String BAD_REQUEST_400 = "pippo/400badRequest";
+public final static String UNAUTHORIZED_401 = "pippo/401unauthorized";
+public final static String PAYMENT_REQUIRED_402 = "pippo/402paymentRequired";
+public final static String FORBIDDEN_403 = "pippo/403forbidden";
+public final static String NOT_FOUND_404 = "pippo/404notFound";
+public final static String METHOD_NOT_ALLOWED_405 = "pippo/405methodNotAllowed";
+public final static String CONFLICT_409 = "pippo/409conflict";
+public final static String GONE_410 = "pippo/410gone";
+public final static String INTERNAL_ERROR_500 = "pippo/500internalError";
+public final static String NOT_IMPLEMENTED_501 = "pippo/501notImplemented";
+public final static String OVERLOADED_502 = "pippo/502overloaded";
+public final static String SERVICE_UNAVAILABLE_503 = "pippo/503serviceUnavailable";
+```
+
+Each template engine implementation comes with above templates. For example if we take a look at `pippo-template-parent/pippo-freemarker/src/main/resources` we can see:
+```
+$ tree .
+.
+└── templates
+    └── pippo
+        ├── 000base.ftl
+        ├── 400badRequest.ftl
+        ├── 401unauthorized.ftl
+        ├── 402paymentRequired.ftl
+        ├── 403forbidden.ftl
+        ├── 404notFound.ftl
+        ├── 405methodNotAllowed.ftl
+        ├── 409conflict.ftl
+        ├── 410gone.ftl
+        ├── 500internalError.ftl
+        ├── 501notImplemented.ftl
+        ├── 502overloaded.ftl
+        └── 503serviceUnavailable.ftl
+```
+
+If you use `FreemarkerTemplateEngine` in your application and you want to replace/override the content of `404notFound.ftl` template,
+then place your variant of `404notFound.ftl` in your `src/main/resources/templates/pippo` directory.
+
+If you are not happy with this fine granularity (a template for each HTTP error code), then you can create your custom `ErrorHandler` that returns the same template for any status code:
+```java
+public class MyErrorHandler extends DefaultErrorHandler {
+    
+    public ExampleErrorHandler(Application application) {
+        super(application);
+    }
+
+    @Override
+    protected String getTemplateForStatusCode(int statusCode) {
+        return "error.ftl"; // or simple "error" without extension
+    }
+    
+}
+```
+
+and use your custom error handler in your application:
+```java
+public class MyApplication extends Application {
+    
+    @Override
+    protected void onInit() {
+        setErrorHandler(new MyErrorHandler(this));
+        
+        // add routes below
+    }
+    
+}
+```