## An app with callbacks { #an-app-with-callbacks }

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

import org.codelibs.fess.Constants;
import org.codelibs.fess.app.pager.FileConfigPager;
import org.codelibs.fess.app.service.FileConfigService;
import org.codelibs.fess.app.web.CrudMode;
import org.codelibs.fess.app.web.api.ApiResult;
import org.codelibs.fess.app.web.api.ApiResult.ApiConfigResponse;
import org.codelibs.fess.app.web.api.ApiResult.ApiResponse;
import org.codelibs.fess.app.web.api.ApiResult.ApiUpdateResponse;

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.keymatch;

import org.codelibs.fess.app.web.api.admin.BaseSearchBody;

/**
 * Search request body for key match administration API.
 */
public class SearchBody extends BaseSearchBody {

    /**
     * Default constructor.

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.labeltype;

import org.codelibs.fess.app.web.admin.labeltype.CreateForm;

/**
 * Request body for creating label type via REST API.
 * Extends CreateForm to inherit validation and field definitions.
 */

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.role;

import org.codelibs.fess.app.web.admin.role.CreateForm;

/**
 * Request body for creating role via REST API.
 * Extends CreateForm to inherit validation and field definitions.
 */

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.webconfig;

import org.codelibs.fess.app.web.admin.webconfig.CreateForm;

/**
 * Request body for creating web configuration via REST API.
 * Extends CreateForm to inherit validation and field definitions.
 */

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.boostdoc;

import org.codelibs.fess.app.web.admin.boostdoc.CreateForm;

/**
 * Request body for creating boost document via REST API.
 * Extends CreateForm to inherit validation and field definitions.
 */

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.dict.kuromoji;

import org.codelibs.fess.app.web.admin.dict.kuromoji.CreateForm;

/**
 * Request body for creating kuromoji dictionary via REST API.
 * Extends CreateForm to inherit validation and field definitions.
 */

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.dict.mapping;

import org.codelibs.fess.app.web.api.admin.dict.BaseSearchDictBody;

/**
 * Search request body for mapping dictionary administration.
 * Extends BaseSearchDictBody with mapping dictionary-specific search parameters.
 */

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.api.admin.dict.stopwords;

import org.codelibs.fess.app.web.admin.dict.stopwords.CreateForm;

/**
 * Request body for creating stop words dictionary via REST API.
 * Extends CreateForm to inherit validation and field definitions.
 */