Database :

entity Students : cuid {
 StudentId: String(6);
 FirstName: String;
 LastName: String;
 DOB: Date;
 Address: String;
}

Service:
service StudentsSrv {
@cds.persistence.skip
@odata.singleton
 entity ExcelUpload {
        @Core.MediaType : 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'
        excel : LargeBinary;
    };

entity Students as projection on db.Students
}

Service.js: ( Custom Handlers)

srv.on('PUT', “ExcelUpload", async (req, next) => {
        if (req.data.excel) {
            var entity = req.headers.slug;
            const stream = new PassThrough();
            var buffers = [];
            req.data.excel.pipe(stream);
            await new Promise((resolve, reject) => {
                stream.on('data', dataChunk => {
                    buffers.push(dataChunk);
                });
                stream.on('end', async () => {
                    var buffer = Buffer.concat(buffers);
                    var workbook = XLSX.read(buffer, { type: "buffer", cellText: true, cellDates: true, dateNF: 'dd"."mm"."yyyy', cellNF: true, rawNumbers: false });
                    let data = []
                    const sheets = workbook.SheetNames
                    for (let i = 0; i < sheets.length; i++) {
                        const temp = XLSX.utils.sheet_to_json(
                            workbook.Sheets[workbook.SheetNames[i]], { cellText: true, cellDates: true, dateNF: 'dd"."mm"."yyyy', rawNumbers: false })
                        temp.forEach((res, index) => {
                            if (index === 0) return;
                            data.push(JSON.parse(JSON.stringify(res)))
                        })
                    }
                    if (data) {
                            const responseCall = await CallEntity(entity, data);
                            if (responseCall == -1)
                                reject(req.error(400, JSON.stringify(data)));
                            else {
                                resolve(req.notify({
                                    message: 'Upload Successful',
                                    status: 200
                                }));   
                        }
                    }
                });
            });
        } else {
            return next();
        }
    });

 srv.before('POST', 'Students', async (req) => {
       //Custom validations can be put, if required before upload
 };
 srv.on('POST', 'Students', async (req) => {
     //return reponse to excel upload entity .
    });

 async function CallEntity(entity, data) {
    if (entity === Students) {
      //If any custom handling required for a particular entity
    }
    const insertQuery = INSERT.into(entity).entries(data); 
    // This calls the service handler of respective entity. It can be used if any custom 
    validations need to be performed. or else custom handlers can be skipped. 
    
    let srv = await cds.connect.to('StudentsSrv');
    const insertResult = await srv.run(insertQuery);
    let query = SELECT.from(entity);
    await srv.run(query);
    return insertResult; //returns response to excel upload entity
   
};

CAP APP Artifacts: Create a list report application using fiori template and extend the application to add custom upload button on the list page.

Manifest.json
     "controlConfiguration": {
                                "@com.sap.vocabularies.UI.v1.LineItem": {
                                    "actions": {
                                        "Upload": {
                                            "id": "UploadButton",
                                            "text": "Upload",
                                            "press": "com.test.ExtensionController.Upload",
                                            "requiresSelection": false
                                        },
ExcelUploadDialog.fragment.xml:
<core:FragmentDefinition xmlns:core="sap.ui.core"
    xmlns:u="sap.ui.unified"
    xmlns="sap.m">
    <Dialog id="_IDDialog"
        title=“Excel Upload"
        class="sapUiResponsiveContentPadding"
        beforeOpen=".onBeforeOpen"
        afterClose=".onAfterClose">
        <content>
            <u:FileUploader id="uploader"
                fileType="xlsx"
                multiple="false"
                uploadUrl=“StudentsSrv/ExcelUpload/excel"
                fileAllowed=".onFileAllowed"
                fileEmpty=".onFileEmpty"
                uploadComplete=".onUploadComplete"
                typeMissmatch=".onTypeMismatch"
                sendXHR="true"
                useMultipart="false"
                placeholder="Choose a xlsx file..."
                httpRequestMethod="Put" />
        </content>
        <beginButton>
            <Button id="ok"
                text="OK"
                press=".onOk"
                type="Emphasized"
                enabled="false" />
        </beginButton>
        <endButton>
            <Button id="cancel"
                text="Cancel"
                press=".onCancel" />
        </endButton>
    </Dialog>
</core:FragmentDefinition>


ExtensionController:
sap.ui.define(["sap/m/MessageBox", "sap/m/MessageToast", "sap/ui/core/UIComponent"],
    function (MessageBox, MessageToast, UIComponent) {
        "use strict";
        function _createUploadController(oExtensionAPI, Entity) {
            var oUploadDialog;

            function setOkButtonEnabled(bOk) {
                oUploadDialog && oUploadDialog.getBeginButton().setEnabled(bOk);
            }

            function setDialogBusy(bBusy) {
                oUploadDialog.setBusy(bBusy)
            }

            function closeDialog() {
                oUploadDialog && oUploadDialog.close()
            }

            function showError(code, target, sMessage) {
                MessageBox.error("Upload failed", {title: "Error"}
            }

            function byId(sId) {
                return sap.ui.core.Fragment.byId("excelUploadDialog", sId);
            }

            return {
                onBeforeOpen: function (oEvent) {
                    oUploadDialog = oEvent.getSource();
                    oExtensionAPI.addDependent(oUploadDialog);
                },

                onAfterClose: function (oEvent) {
                    oExtensionAPI.removeDependent(oUploadDialog);
                    oUploadDialog.destroy();
                    oUploadDialog = undefined;
                },

                onOk: function (oEvent) {
                    setDialogBusy(true)

                    var oFileUploader = byId("uploader");
                    var headPar = new sap.ui.unified.FileUploaderParameter();
                    headPar.setName('slug');
                    headPar.setValue(Entity);
                    oFileUploader.removeHeaderParameter('slug');
                    oFileUploader.addHeaderParameter(headPar);
                    var sUploadUri = oExtensionAPI._controller.extensionAPI._controller._oAppComponent.getManifestObject().resolveUri(“./StudentsSrv/ExcelUpload/excel")
                    oFileUploader.setUploadUrl(sUploadUri);
                    oFileUploader
                        .checkFileReadable()
                        .then(function () {
                            oFileUploader.upload();
                        })
                        .catch(function (error) {
                            showError("The file cannot be read.");
                            setDialogBusy(false)
                        })
                },

                onCancel: function (oEvent) {
                    closeDialog();
                },

                onTypeMismatch: function (oEvent) {
                    var sSupportedFileTypes = oEvent
                        .getSource()
                        .getFileType()
                        .map(function (sFileType) {
                            return "*." + sFileType;
                        })
                        .join(", ");

                    showError(
                        "The file type *." +
                        oEvent.getParameter("fileType") +
                        " is not supported. Choose one of the following types: " +
                        sSupportedFileTypes
                    );
                },

                onFileAllowed: function (oEvent) {
                    setOkButtonEnabled(true)
                },

                onFileEmpty: function (oEvent) {
                    setOkButtonEnabled(false)
                },

                onUploadComplete: function (oEvent) {
                    var iStatus = oEvent.getParameter("status");
                    var oFileUploader = oEvent.getSource()

                    oFileUploader.clear();
                    setOkButtonEnabled(false)
                    setDialogBusy(false)

                    if (iStatus >= 400) {
                        var oRawResponse;
                        try {
                            oRawResponse = JSON.parse(oEvent.getParameter("responseRaw"));
                        } catch (e) {
                            oRawResponse = oEvent.getParameter("responseRaw");
                        }
                        if (oRawResponse && oRawResponse.error && oRawResponse.error.message) {
                            showError(oRawResponse.error.code, oRawResponse.error.target, oRawResponse && oRawResponse.error && oRawResponse.error.message);
                        }
                    } else {
                        MessageToast.show("File uploaded successfully");
                        oExtensionAPI.refresh()
                        closeDialog();
                    }
                }
            };
        };

        return {
            Upload: function (oBindingContext, aSelectedContexts) {
                this.loadFragment({
                    id: “excelUploadDialog",
                    name: "com.test.ExcelUploadDialog",
                    controller: _createUploadController(this, ‘Students’)
                }).then(function (oDialog) {
                    oDialog.open();
                });
            }
        };
    });

Summary:

This blog contains code snippets useful for uploading data into tables from excel. We have used a single upload entity which can be re-used for upload of data into various entities. The Upload custom handler parses the uploaded excel using File Uploader and helps to insert that data into respective entity.

References:

https://github.com/SAP-samples/cloud-cap-samples-java/blob/main/app/admin/webapp/extension/Upload.js