HTML file is not generated in the extent report

Question

I have made a script to generate an extent report, but HTML is not generated.

Please check below code:

Report.java:
package report;

import org.testng.Assert;
import org.testng.ITestResult;
import org.testng.SkipException;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.AfterTest;
import org.testng.annotations.BeforeTest;
import org.testng.annotations.Test;
import com.aventstack.extentreports.ExtentReports;
import com.aventstack.extentreports.ExtentTest;
import com.aventstack.extentreports.Status;
import com.aventstack.extentreports.markuputils.ExtentColor;
import com.aventstack.extentreports.markuputils.MarkupHelper;
import com.aventstack.extentreports.reporter.ExtentHtmlReporter;
import com.aventstack.extentreports.reporter.configuration.ChartLocation;
import com.aventstack.extentreports.reporter.configuration.Theme;

public class Report {

    ExtentHtmlReporter htmlReporter;
     static ExtentReports extent;
     static ExtentTest logger;


     @BeforeTest
     public void startReport(){

     htmlReporter = new ExtentHtmlReporter(System.getProperty("user.dir") +"/test-output/STMExtentReport.html");
     extent = new ExtentReports ();
     extent.attachReporter(htmlReporter);
     extent.setSystemInfo("Host Name", "SoftwareTestingMaterial");
     extent.setSystemInfo("Environment", "Automation Testing");
     extent.setSystemInfo("User Name", "Rajkumar SM");

     htmlReporter.config().setDocumentTitle("Title of the Report Comes here");
     htmlReporter.config().setReportName("Name of the Report Comes here");
     htmlReporter.config().setTestViewChartLocation(ChartLocation.TOP);
     htmlReporter.config().setTheme(Theme.STANDARD);
     }

     @Test
     public void passTest(){
     logger = extent.createTest("passTest");
     Assert.assertTrue(true);
     logger.log(Status.PASS, MarkupHelper.createLabel("Test Case Passed is passTest", ExtentColor.GREEN));
     }

     @Test
     public void failTest(){
     logger = extent.createTest("failTest");
     Assert.assertTrue(false);
     logger.log(Status.PASS, "Test Case (failTest) Status is passed");
     logger.log(Status.PASS, MarkupHelper.createLabel("Test Case (failTest) Status is passed", ExtentColor.GREEN));
     }

     @Test
     public void skipTest(){
     logger = extent.createTest("skipTest");
     throw new SkipException("Skipping - This is not ready for testing ");
     }

     @AfterMethod
     public void getResult(ITestResult result){
     if(result.getStatus() == ITestResult.FAILURE){
     //logger.log(Status.FAIL, "Test Case Failed is "+result.getName());
     //MarkupHelper is used to display the output in different colors
     logger.log(Status.FAIL, MarkupHelper.createLabel(result.getName() + " - Test Case Failed", ExtentColor.RED));
     logger.log(Status.FAIL, MarkupHelper.createLabel(result.getThrowable() + " - Test Case Failed", ExtentColor.RED));
     }else if(result.getStatus() == ITestResult.SKIP){
     //logger.log(Status.SKIP, "Test Case Skipped is "+result.getName());
     logger.log(Status.SKIP, MarkupHelper.createLabel(result.getName() + " - Test Case Skipped", ExtentColor.ORANGE)); 
     }
     }
     @AfterTest
     public void endReport(){
     extent.flush();
        }


}

The .xml file :

<?xml version="1.0" encoding="UTF-8"?>
<extentreports>
    <configuration>
        <!-- report theme -->
        <!-- standard, dark -->
        <theme>standard</theme>

        <!-- document encoding -->
        <!-- defaults to UTF-8 -->
        <encoding>UTF-8</encoding>

        <!-- protocol for script and stylesheets -->
        <!-- defaults to https -->
        <protocol>https</protocol>

        <!-- title of the document -->
        <documentTitle>Extent</documentTitle>

        <!-- report name - displayed at top-nav -->
        <reportName>Automation Report</reportName>

        <!-- location of charts in the test view -->
        <!-- top, bottom -->
        <testViewChartLocation>bottom</testViewChartLocation>

        <!-- custom javascript -->
        <scripts>
            <![CDATA[
                $(document).ready(function() {

                });
            ]]>
        </scripts>

        <!-- custom styles -->
        <styles>
            <![CDATA[

            ]]>
        </styles>
    </configuration>
</extentreports>

Answer 1

I have created an example on the basis of your code, please note that here i'm using the Extent Report Version 3 so change your code accordingly.
I hope this code help you-

public class Report  {

     static ExtentTest logger;
     static ExtentReports extent;
     static ExtentHtmlReporter reporter;
    @BeforeClass
    public void startreport() {

        extent = new ExtentReports();       
        extent.attachReporter(getHtmlReporter());
        extent.setSystemInfo("Host Name", "SoftwareTestingMaterial");
        extent.setSystemInfo("Environment", "Automation Testing");
        extent.setSystemInfo("User Name", "Rajkumar SM");               
    }
     public ExtentHtmlReporter getHtmlReporter()
    {
        reporter= new ExtentHtmlReporter(System.getProperty("user.dir") +"\\test-output/STMExtentReport.html");
        reporter.config().setChartVisibilityOnOpen(true);
        reporter.config().setDocumentTitle("QA Automation Report");
        reporter.config().setReportName("Regression Testing");
        reporter.config().setTheme(Theme.STANDARD);
        return reporter;
    }
     @Test
    public void passTest(){
         logger= extent.createTest("Pass Test", "Login");
    //test steps.
     }
     @Test
    public void failTest(){
    logger = extent.createTest("failTest", "Login");
     //test steps.
     }

     //other steps

     @AfterTest
    public void endReport(){
    extent.flush();
       }
}  

Please refresh your project after run the test.
For the more information about report please check Here