Passing javascript object containing another array of objects to localStorage and then to java servlet using ajax

Question

I am trying to work out how to store a javascript object in local storage that has a few items as well as an array of objects, if that is possible. To then extract the data from the local storage and send to a java servlet using ajax, then extract the data from the java HttpServletRequest. Here is some of the code I have written. It's a bit too complex to put the entire code base here. I have multiple forms which a user completes and as they move between forms I store the data entered into local storage.

const object = localStorage.getItem(scenarioName);
let scenarioObject = JSON.parse(object);

if (formIsValid) {
            scenarioObject.SUPER_BALANCE = 420000;
            scenarioObject.SUPER_INVESTMENT_FEES = 0.14;
            scenarioObject.SUPER_ADMIN_FEES = 120;
            scenarioObject.LIFE_INSURANCE = 200000;
            scenarioObject.ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION = 1500;

        let objectString = JSON.stringify(scenarioObject);
        localStorage.setItem(scenarioName, objectString);

}

To extract the data from local storage I do the following:

const object = localStorage.getItem(activeScenario);
    const jsonString = JSON.parse(object);

    const yourSuperBalance = jsonString.SUPER_BALANCE;
    $("#your-super-balance").val(yourSuperBalance);

    const yourInvestmentFees = jsonString.SUPER_INVESTMENT_FEES;
    $("#super-investment-fees").val(yourInvestmentFees);

    const yourSuperAdminFees = jsonString.SUPER_ADMIN_FEES;
    $("#super-admin-fees").val(yourSuperAdminFees);

    const yourInsurance = jsonString.LIFE_INSURANCE;
    $("#life-insurance").val(yourInsurance);

    const yourAnnualSuperContribution = jsonString.ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION;
    $("#your-annual-lump-sum-super-contribution").val(yourAnnualSuperContribution);

This all works fine, but now I wanted to add an array of objects from a table. I could not figure out a way to add this so I ended up storing two items in local storage. One for all the form data and one for the table data. I didn't like this approach but couldn't get it to work otherwise. Here is how I did the table:

function getSuperContributionsTableDataString(table) {
    let yourSuperContributionsTableData = [];
    let jsonData;
    // commence for loop at 1 because the first row will be the header row and we want to skip that
    for (let i = 1; i < table.rows.length; i++) {
        let row = table.rows[i];
        // first check all cells in row have a value, if not ignore
        if (row.cells[0].innerText !== "" && row.cells[1].innerText !== "" && row.cells[2].innerText !== "") {
            // As we are pushing the last element pushed becomes the first element in the array
            // therefore, we push the before or after tax first and age last
            jsonData = {};
            jsonData[SUPER_TAXATION_CONTRIBUTION] = row.cells[2].innerText;
            jsonData[SUPER_AMOUNT_CONTRIBUTION] = row.cells[1].innerText;
            jsonData[SUPER_AGE_CONTRIBUTION] = row.cells[0].innerText;
            yourSuperContributionsTableData.push(jsonData);
        }
    }
    return JSON.stringify(yourSuperContributionsTableData);
}
let superContributionsTableDataString = getSuperContributionsTableDataString(
                document.getElementById("your-extra-super-contributions-table"));

localStorage.setItem(scenarioName+ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION, superContributionsTableDataString);

This all worked but then I had to figure out how to send this data to the server using ajax. Without the table, everything was working fine as follows:

function sendScenarioDetailsToServer() {
    let activeScenario = localStorage.getItem(ACTIVE_SCENARIO_KEY);
    let item = localStorage.getItem(activeScenario);
    let passedData = JSON.parse(item);

    
    $.ajax({
        type: "POST",
        url: "ScenarioServlet",
        data: passedData,
        success: function (data) {
            const SUCCESS_INT = data.length - 1;
            if (data[SUCCESS_INT].SUCCESS === FAIL) {
                displayPopupMessage("Error saving scenario ", "Save Scenario");
            }else {
                displayResult();
            }

        },
        error: function (error, status) {
            console.log(`Error ${error}`);
            const stackTrace = getStackTrace();
            const message = "An error occurred sending your data to the server for calculation. ";
            displayPopupMessage(message, "Server Error.", stackTrace);
        }
    });

}

I modified this function as follows to add the table data and everything in the java servlet code went wrong.

function sendScenarioDetailsToServer() {
    let activeScenario = localStorage.getItem(ACTIVE_SCENARIO_KEY);
    let item = localStorage.getItem(activeScenario);
    let passedData = JSON.parse(item);

    // superannuation table
    const superTable = activeScenario+ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION;

    // this is already stringified
    const superTableItem = localStorage.getItem(superTable);
    const superTableData = '&' + ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION + "=" + superTableItem;

    const formData = passedData + superTableData;
    console.log("formData " + formData);


    $.ajax({
        type: "POST",
        url: "ScenarioServlet",
        data: passedData + superTableData,
        success: function (data) {
            const SUCCESS_INT = data.length - 1;
            if (data[SUCCESS_INT].SUCCESS === FAIL) {
                // TODO display messages
                displayPopupMessage("Error saving scenario ", "Save Scenario");
            }else {
                displayResult();
            }
        },
        error: function (error, status) {
            console.log(`Error ${error}`);
            const stackTrace = getStackTrace();
            const message = "An error occurred sending your data to the server for calculation. ";
            displayPopupMessage(message, "Server Error.", stackTrace);
        }
    });

}

Can anyone advise how best to store a javascript object in local storage that has an item inside the object which is an array of objects for a table? How do I store this in local storage, retrieve it from local storage, send it to the java servlet using ajax and then retrieve it from the HttpServletRequest. Any assistance would be much appreciated.

Answer 1

I worked out a way to do this. I shall fully explain the situation and then my solution to the problem. Not sure if this is the best solution but it does work. The situation is that I have multiple forms where the user enters data for calculations, including a table of data. I wanted to store this data on local storage for later retrieval next time the user uses the website. The calculations are done in Java on the server so when the user clicks on something like "calculate" the data in local storage is then sent to the server to perform the calculations and the result is sent back. I needed to store a javascript object containing some elements plus a table, so basically a javascript object with an array inside it.

Collect data from the table

function getSuperContributionsTableDataString(table) {
    let yourSuperContributionsTableData = [];
    let jsonData;
    // commence for loop at 1 because the first row will be the header row and we want to skip that
    for (let i = 1; i < table.rows.length; i++) {
        let row = table.rows[i];
        // first check all cells in row have a value, if not ignore
        if (row.cells[0].innerText !== "" && row.cells[1].innerText !== "" && row.cells[2].innerText !== "") {
            // As we are pushing the last element pushed becomes the first element in the array
            // therefore, we push the before or after tax first and age last
            jsonData = {};
            jsonData[SUPER_TAXATION_CONTRIBUTION] = row.cells[2].innerText;
            jsonData[SUPER_AMOUNT_CONTRIBUTION] = row.cells[1].innerText;
            jsonData[SUPER_AGE_CONTRIBUTION] = row.cells[0].innerText;
            yourSuperContributionsTableData.push(jsonData);
        }
    }
    return yourSuperContributionsTableData;
}

Where I went wrong with this originally was I stringified the array. As the entire javascript object is going to be stringified this was unnecessary.

Create javascript object and store in local storage The first step is to extract the item from local storage to update it with the new data from the user. Notice we must parse the object because it was originally stringified. Secondly set the user entered data on the javascript object. You will notice the call to the function above that retrieves the table data. That table data is set as a key value pair in the javascript object.

const scenarioName = localStorage.getItem(ACTIVE_SCENARIO_KEY);
const object = localStorage.getItem(scenarioName);
let scenarioObject = JSON.parse(object);
isValid = validateYourSuperannuationForm();
if (isValid) {
            let superContributionsTableDataString = getSuperContributionsTableDataString(
                document.getElementById("your-extra-super-contributions-table"));

            scenarioObject.SUPER_BALANCE = $("#your-super-balance").val();
            scenarioObject.SUPER_INVESTMENT_FEES = $("#super-investment-fees").val();
            scenarioObject.SUPER_ADMIN_FEES = $("#super-admin-fees").val();
            scenarioObject.LIFE_INSURANCE = $("#life-insurance").val();
            scenarioObject.ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION = $("#your-annual-lump-sum-super-contribution").val();
            scenarioObject.EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA = superContributionsTableDataString;

            let objectString = JSON.stringify(scenarioObject);
            localStorage.setItem(scenarioName, objectString);
        }

Send item in local storage to server I discovered trying to stringify the entire javascript object caused problems at the server. What I had to do was create a new object for the formData to be sent to the server, BUT I had to stringify only the table data, not the entire object. I had to retrieve each item from local storage and set it on the formData object to be passed to the server.

function sendScenarioDetailsToServer() {
    const activeScenario = localStorage.getItem(ACTIVE_SCENARIO_KEY);
    const item = localStorage.getItem(activeScenario);
    const scenarioObject = JSON.parse(item);

    // We must do this because if superContributionsTableData == "" and we then stringify this it will
    // end up with a value of """", which will cause an error.
    const superContributionsTableData = scenarioObject.EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA;
    let superContributionsTableDataString = "";
    if (superContributionsTableData !== ""){
        superContributionsTableDataString = JSON.stringify(superContributionsTableData);
    }
    const formData = {
        SCENARIO_NAME: scenarioObject.SCENARIO_NAME,
        DATE_OF_BIRTH: "",
        IS_SINGLE:  scenarioObject.IS_SINGLE,
        IS_RETIRED: scenarioObject.IS_RETIRED,
        RETIREMENT_DATE: scenarioObject.RETIREMENT_DATE,
        IS_HOMEOWNER: scenarioObject.IS_HOMEOWNER,
        FORTNIGHTLY_RENT: scenarioObject.FORTNIGHTLY_RENT,
        DATE_RENT_CEASES: scenarioObject.DATE_RENT_CEASES,
        IS_SINGLE_AND_SHARING: scenarioObject.IS_SINGLE_AND_SHARING,
        SPOUSE_DATE_OF_BIRTH: scenarioObject.SPOUSE_DATE_OF_BIRTH,
        IS_SPOUSE_RETIRED: scenarioObject.IS_SPOUSE_RETIRED,
        SPOUSE_RETIREMENT_DATE: scenarioObject.SPOUSE_RETIREMENT_DATE,
        SUPER_BALANCE: scenarioObject.SUPER_BALANCE,
        SUPER_INVESTMENT_FEES: scenarioObject.SUPER_INVESTMENT_FEES,
        SUPER_ADMIN_FEES: scenarioObject.SUPER_ADMIN_FEES,
        LIFE_INSURANCE: scenarioObject.LIFE_INSURANCE,
        ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION: scenarioObject.ANNUAL_LUMP_SUM_SUPER_CONTRIBUTION,
        EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA: superContributionsTableDataString
}
$.ajax({
        type: "POST",
        url: "ScenarioServlet",
        data: formData,

        success: function (data) {
        // do stuff here

       {
},
        error: function (error, status) {
            console.log(`Error ${error}`);
            const stackTrace = getStackTrace();
            const message = "An error occurred sending your data to the server for calculation. ";
            displayPopupMessage(message, "Server Error.", stackTrace);
        }
    });

In the Java Servlet the data is then extracted from the HttpServletRequest passed to the doPost method. It is retrieved in the usual way by calling HttpServletRequest.getParameter. Converting the table data is a little more complex because it is an array that was converted to a string. I am including an extract of that code in case it is of use to someone.

       ArrayList<LumpSumSuperContribution> superContributionsList = new ArrayList<>();
        String superContributionsTableData = request.getParameter(EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA);
       // Array superContributionsArray = request.getParameter(EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA);
        JSONObject superContributionsMessage = new JSONObject();
        boolean errorOccurred = false;
        if (superContributionsTableData != null && superContributionsTableData.length() > 0) {
            try {
                JSONArray superContributionsArray = new JSONArray(superContributionsTableData);
                int i = 0;
                while (i < superContributionsArray.length()) {
                    JSONObject contributionObj = (JSONObject) superContributionsArray.get(i);
                    String ageString = (String) contributionObj.get(SUPER_AGE_CONTRIBUTION);
                    Validator.WholeNumberResult result6 = Validator.validateMandatoryWholeNumber(ageString, 18, 99,
                            "Lump Sum Super Contribution age for row " + (i + 1));
                    if (!result6.getErrorMessage().equals(SUCCESS)) {
                        superContributionsMessage.put(EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA, result6.getErrorMessage());
                        messageArray.put(superContributionsMessage);
                        errorOccurred = true;
                        break;
                    }
                    Integer age = result6.getNumber();
String contributionAmountString = (String) contributionObj.get(SUPER_AMOUNT_CONTRIBUTION);
                    Validator.WholeNumberResult result7 = Validator.validateMandatoryWholeNumber(
                            contributionAmountString, 1, 9999999,
                            "Lump Sum Super Contribution amount for row " + (i + 1));
                    if (!result7.getErrorMessage().equals(SUCCESS)) {
                        superContributionsMessage.put(EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA, result7.getErrorMessage());
                        messageArray.put(superContributionsMessage);
                        errorOccurred = true;
                        break;
                    }
                    Integer amount = result7.getNumber();

                    String beforeAfterTaxString = (String) contributionObj.get(SUPER_TAXATION_CONTRIBUTION);
                    Validator.TextResult result8 = Validator.validateMandatoryText(beforeAfterTaxString,
                            "Lump Sum Super Contribution Before or After Tax for row " + (i + 1), 5, 6);
                    if (!result8.getErrorMessage().equals(SUCCESS)) {
                        superContributionsMessage.put(EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA, result8.getErrorMessage());
                        messageArray.put(superContributionsMessage);
                        errorOccurred = true;
                        break;
                    }
                    String beforeAfterTax = result8.getText();
LumpSumSuperContribution superContribution = new LumpSumSuperContribution(age, amount, false,
                            LumpSumSuperContribution.YOUR_CONTRIBUTION, beforeAfterTax);

                    superContributionsList.add(superContribution);

                    i++;
                }
                if (!errorOccurred) {
                    scenario.setAllYourSuperContributions(superContributionsList);
                    //  superContributionsMessage.put(EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA, SUCCESS);
                } else {
                    fail = true;
                    superContributionsMessage.put(EXTRA_SUPER_CONTRIBUTIONS_TABLE_DATA, FAIL);
                    messageArray.put(superContributionsMessage);
                }

            } catch (JSONException e) {
                throw new RuntimeException(e);
            }
        }else {
            scenario.setAllYourSuperContributions(null);
        }
}

Summary

1. Create a javascript array. Then loop through the table data and create a javascript object for each row of the table and push onto the array.
2. Create or retrieve javascript object stored in local storage. If already in local storage, this object must be parsed using JSON.parse(object).
3. Set the details on the object entered by the user.
4. Stringify the javascript array and add the string to the object as a key value pair.
5. To send the data to the server retrieve the item from local storage and parse the item to extract details from it.
6. Set the extracted details on a newly created formData object.
7. Stringify the table data and set as a key value pair in formData.
8. Using ajax Post the data to the server.

I hope this helps someone in the future. It took me a while of trying different things to find a way to get this to work. If anyone has a better solution please post it.