# Create Hooks for MultiServiceAppHandler

The Multisite APIs provide an option to write custom pre- and post-hooks for each API to implement custom logic. A pre-hook is run before the actual API runs. A post-hook runs after the actual API runs.

1. Write the custom class to implement the pre and post hook.

   Example code:

   ```nolang
   1 global with sharing class MSCustomHookImplementation implements vlocity_cmt.VlocityOpenInterface
   2 {
   3  global Boolean invokeMethod(String methodName, Map<String, Object> input, Map<String, Object> output, Map<String, Object> options)
   4  {
   5    if( methodName.equalsIgnoreCase('getGroups.PreInvoke'))
   6    {
   7      getGroups_PreInvoke(methodName, input, output,options);
   8      return true;
   9    }
   10
   11    if( methodName.equalsIgnoreCase('getGroups.PostInvoke'))
   12    {
   13      getGroups_PostInvoke(methodName, input, output,options);
   14      return true;
   15    }
   16
   17    return false;
   18  }
   19
   20  private void getGroups_PreInvoke(String methodName, Map<String, Object> input, Map<String, Object> output, Map<String, Object> options)
   21  {
   22    //This method gets called before getGroups
   23  }
   24  private void getGroups_PostInvoke(String methodName, Map<String, Object> input, Map<String, Object> output, Map<String, Object> options)
   25  {
   26    //This method gets called after getGroups
   27  }

   ```

2. Create the interface implementation.

   1. From the App Launcher, click **Interface Implementations**.

   2. Click **New**.

   3. In the New Interface Implementation dialog, enter the following:

      - **Interface Name:** MSAppHandlerHookInterface

      - **Active Implementation Class:** MSCustomHookImplementation (Name of Custom Class)

   4. Click **Save**.

3. Create a new Interface Implementation Detail for the interface created above.

   1. On the Related tab for your new custom interface implementation, click **New**.

   2. In the New Interface Implementation Detail dialog, enter MSCustomHookImplementation for **Available Implementation**.

   3. Click **Active** to make this implementation the active implementation.

   4. Click **Save**.