我收到异常 java.util.LinkedHashMap cannot be cast to java.util.List on console

Question

Controller Class Method

@RequestMapping(value="generics",method=RequestMethod.POST,produces="application/json",consumes="application/json")
public String generics(@RequestBody List<Object> objectlist) throws NoSuchFieldException, SecurityException, IOException
{
    System.out.println("controller:"+objectlist);
    return class1service.generics(objectlist);

}

Service Class Method`

 public String generics(List<Object> objectlist) throws NoSuchFieldException, SecurityException, IOException
    {
        System.out.println("service"+objectlist);
        return class1dao.generics(objectlist);
    }

Method for checking the particuler entity class and Calling the method which will generate the excel sheet for that Objects

public String generics(List<?> clazz) throws IOException, NoSuchFieldException, SecurityException
{
    System.out.println("generics:"+clazz);
    try
    { 
    List<Class1> ll1=new ArrayList<Class1>();
    List<Class2> ll2=new ArrayList<Class2>();
    List<Class3> ll3=new ArrayList<Class3>();
    System.out.println("generics:"+clazz);
    System.out.println("in generics for loop");

            for (int i = 0; i < clazz.size(); i++)
            {

                System.out.println("in clazz loop");

                System.out.println("in clazz loop i:"+i);

                System.out.println("befor clazz.get(i)"+(clazz.get(i)));

                System.out.println("clazz instanceof List<?>"+(clazz instanceof List<?>));
                if (clazz instanceof List<?>)
                {

                    List<Class1>    a2=  (List<Class1>) clazz.get(i);
                    //ArrayList<Class1> a2=(ArrayList<Class1>) clazz.get(i);
                    Class1 c1=new Class1();
                    c1.setS1Id(((Class1) a2.get(i)).getS1Id());
                    System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getS1Id()));
                    c1.setStudentName(((Class1) a2.get(i)).getStudentName());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getStudentName()));
                     c1.setStudentAge(((Class1) a2.get(i)).getStudentAge());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getStudentAge()));
                     c1.setEnglish(((Class1) a2.get(i)).getEnglish());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getEnglish()));
                     c1.setKannada(((Class1) a2.get(i)).getKannada());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getKannada()));
                     c1.setHindi(((Class1) a2.get(i)).getMathematics());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getMathematics()));
                     c1.setScience(((Class1) a2.get(i)).getScience());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getScience()));
                     c1.setSocielSience(((Class1) a2.get(i)).getSocielSience());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getSocielSience()));
                     c1.setMathematics(((Class1) a2.get(i)).getMathematics());
                     System.out.println("c1.setS1Id(a1.get(i).getS1Id());"+ (((Class1) a2.get(i)).getMathematics()));
                     ll1.add(c1);
                     System.out.println("after clazz.get(i)"+(clazz.get(i)));
                     // ll1=(List<Class1>) a1;
                     System.out.println("ll1"+ll1);
                    listOfClass1(ll1);


                } 
                else if(clazz instanceof List<?>) {

                     List<Class2> a2=(List<Class2>) clazz.get(i);
                     Class2 c2=new Class2();
                     c2.setS2Id(a2.get(i).getS2Id());
                     c2.setStudentName(a2.get(i).getStudentName());
                     c2.setStudentAge(a2.get(i).getStudentAge());
                     c2.setEnglish(a2.get(i).getEnglish());
                     c2.setKannada(a2.get(i).getKannada());
                     c2.setHindi(a2.get(i).getMathematics());
                     c2.setScience(a2.get(i).getScience());
                     c2.setSocielSience(a2.get(i).getSocielSience());
                     c2.setMathematics(a2.get(i).getMathematics());
                     ll2.add(c2);
                     System.out.println("ll2"+ll2);
                    listOfClass2(ll2);
                }
                else if (clazz instanceof Class3)
                {
                     List<Class3> a3=(List<Class3>) clazz.get(i);
                     Class3 c3=new Class3();
                     c3.setS3Id(a3.get(i).getS3Id());
                     c3.setStudentName(a3.get(i).getStudentName());
                     c3.setStudentAge(a3.get(i).getStudentAge());
                     c3.setEnglish(a3.get(i).getEnglish());
                     c3.setKannada(a3.get(i).getKannada());
                     c3.setHindi(a3.get(i).getMathematics());
                     c3.setScience(a3.get(i).getScience());
                     c3.setSocielSience(a3.get(i).getSocielSience());
                     c3.setMathematics(a3.get(i).getMathematics());
                     ll3.add(c3);
                     System.out.println("ll3"+ll3);
                    listOfClass3(ll3);
                }
         }      
 return "added";
}
catch(Exception e)
{
    System.out.println(e.getMessage());
    return "not added";
}

}

Method for generating excel sheet for Class1 entity Objects

 public void listOfClass1(List<Class1> stud1) throws IOException
 {
     System.out.println("listOfClass1:"+stud1);


     String[] columns = {"s1Id","studentName", "studentAge", "english","kannada","science","mathematics","socielScience","hindi","total","percentage","status"};  
        Workbook workbook = new XSSFWorkbook();
        CreationHelper createHelper = workbook.getCreationHelper();

        Sheet sheet = workbook.createSheet("class1");

          // Create a Font for styling header cells
        Font headerFont = workbook.createFont();
        headerFont.setBold(true);
        headerFont.setFontHeightInPoints((short) 14);
        headerFont.setColor(IndexedColors.RED.getIndex());

    // Create a CellStyle with the font
     CellStyle headerCellStyle = workbook.createCellStyle();
     headerCellStyle.setFont(headerFont);

    // Create a Row
     Row headerRow = sheet.createRow(0);
     System.out.println("");

    // Creating cells
     for(int i = 0; i < columns.length; i++)
     {
      Cell cell = headerRow.createCell(i);
      cell.setCellValue(columns[i]);
      cell.setCellStyle(headerCellStyle);
     }

     int rowCount = sheet.getLastRowNum();

    // FormulaEvaluator evaluator = workbook.getCreationHelper().createFormulaEvaluator();

    // CellReference cellReference = new CellReference("SUM(D2:E2:F2:G2:H2:I2)");
    // Row row = sheet.getRow(cellReference.getRow());
    // Cell cell = row.getCell(cellReference.getCol());
     int rowNum=1;
     int x=2;
     for(Class1 student1:stud1)
     {
     Row row = sheet.createRow(rowNum);

     row.createCell(0).setCellValue(student1.getS1Id());
     System.out.println(student1.getS1Id());
     row.createCell(1).setCellValue(student1.getStudentName());
    // CellValue cellValue = evaluator.evaluate(cell);
     row.createCell(2).setCellValue(student1.getStudentAge());

     row.createCell(3).setCellValue(student1.getEnglish());
     row.createCell(4).setCellValue(student1.getKannada());
     row.createCell(5).setCellValue(student1.getScience());
     row.createCell(6).setCellValue(student1.getMathematics());
     row.createCell(7).setCellValue(student1.getSocielSience());  
    // row.createCell(4, cellValue.getCellType());
     row.createCell(8).setCellValue(student1.getHindi());

     row.createCell(9).setCellFormula("SUM(D"+x+":E"+x+":F"+x+":G"+x+":H"+x+":I"+x+")");//.setCellValue(student1.getTotal());
     row.createCell(10).setCellFormula("((J"+x+")*100)/600");//student1.getPercentage());
     row.createCell(11).setCellValue(true);
     x++;
     rowNum++;
 }
 // Resize all columns to fit the content size
 for(int i = 0; i < columns.length; i++) {
     sheet.autoSizeColumn(i);
 }


 // Write the output to a file
///FileOutputStream fileOut = new FileOutputStream("excelone.xlsx");
String fileOut="C:/Users/Laxmi.Baragukar/Desktop/eclipse_neon/excelclass1.xlsx";

// return str;
//Base64.Encoder data=Base64.getEncoder().;
//String str=data.encodeToString(src)
 //String encode=fetching(fileOut);

 FileOutputStream fileOut1 = new FileOutputStream(fileOut);
 String encode=fetching(fileOut);
 workbook.write(fileOut1);
 fileOut1.close();
 workbook.close();


 //return fileOut;
}

Method for generating excel sheet for Class2 entity Objects

public void listOfClass2(List<Class2> stud1) throws IOException
 {
     System.out.println("listOfClass2:"+stud1);


     String[] columns = {"s2Id","studentName", "studentAge", "english","kannada","science","mathematics","socielScience","hindi","total","percentage","status"};  
        Workbook workbook = new XSSFWorkbook();
        CreationHelper createHelper = workbook.getCreationHelper();

        Sheet sheet = workbook.createSheet("class1");

          // Create a Font for styling header cells
        Font headerFont = workbook.createFont();
        headerFont.setBold(true);
        headerFont.setFontHeightInPoints((short) 14);
        headerFont.setColor(IndexedColors.RED.getIndex());

    // Create a CellStyle with the font
     CellStyle headerCellStyle = workbook.createCellStyle();
     headerCellStyle.setFont(headerFont);

    // Create a Row
     Row headerRow = sheet.createRow(0);
     System.out.println("");

    // Creating cells
     for(int i = 0; i < columns.length; i++)
     {
      Cell cell = headerRow.createCell(i);
      cell.setCellValue(columns[i]);
      cell.setCellStyle(headerCellStyle);
     }

     int rowCount = sheet.getLastRowNum();

    // FormulaEvaluator evaluator = workbook.getCreationHelper().createFormulaEvaluator();

    // CellReference cellReference = new CellReference("SUM(D2:E2:F2:G2:H2:I2)");
    // Row row = sheet.getRow(cellReference.getRow());
    // Cell cell = row.getCell(cellReference.getCol());
     int rowNum=1;
     int x=2;
     for(Class2 student1:stud1)
     {
     Row row = sheet.createRow(rowNum);

     row.createCell(0).setCellValue(student1.getS2Id());
     System.out.println(student1.getS2Id());
     row.createCell(1).setCellValue(student1.getStudentName());
    // CellValue cellValue = evaluator.evaluate(cell);
     row.createCell(2).setCellValue(student1.getStudentAge());

     row.createCell(3).setCellValue(student1.getEnglish());
     row.createCell(4).setCellValue(student1.getKannada());
     row.createCell(5).setCellValue(student1.getScience());
     row.createCell(6).setCellValue(student1.getMathematics());
     row.createCell(7).setCellValue(student1.getSocielSience());  
    // row.createCell(4, cellValue.getCellType());
     row.createCell(8).setCellValue(student1.getHindi());

     row.createCell(9).setCellFormula("SUM(D"+x+":E"+x+":F"+x+":G"+x+":H"+x+":I"+x+")");//.setCellValue(student1.getTotal());
     row.createCell(10).setCellFormula("((J"+x+")*100)/600");//student1.getPercentage());
     row.createCell(11).setCellValue(true);
     x++;
     rowNum++;
 }
 // Resize all columns to fit the content size
 for(int i = 0; i < columns.length; i++) {
     sheet.autoSizeColumn(i);
 }


 // Write the output to a file
///FileOutputStream fileOut = new FileOutputStream("excelone.xlsx");
String fileOut="C:/Users/Laxmi.Baragukar/Desktop/eclipse_neon/excelclass2.xlsx";

// return str;
//Base64.Encoder data=Base64.getEncoder().;
//String str=data.encodeToString(src)
 //String encode=fetching(fileOut);

 FileOutputStream fileOut1 = new FileOutputStream(fileOut);
 String encode=fetching(fileOut);
 workbook.write(fileOut1);
 fileOut1.close();
 workbook.close();


 //return fileOut;
}

Method for generating excel sheet for Class3 entity Objects

 public void listOfClass3(List<Class3> stud1) throws IOException
 {

     System.out.println("listOfClass3:"+stud1);
   /*List<Class3> class1=new ArrayList<Class3>();
   for(Class3 obj:stud1){
       Class3 c1=new Class3();
       c1.setS3Id(obj.getS3Id());
       c1.setStudentName(obj.getStudentName());
       c1.setStudentAge(obj.getStudentAge());
       class1.add(c1);
   }*/
     String[] columns = {"s3Id","studentName", "studentAge", "english","kannada","science","mathematics","socielScience","hindi","total","percentage","status"};  
        Workbook workbook = new XSSFWorkbook();
        CreationHelper createHelper = workbook.getCreationHelper();

        Sheet sheet = workbook.createSheet("class1");

          // Create a Font for styling header cells
        Font headerFont = workbook.createFont();
        headerFont.setBold(true);
        headerFont.setFontHeightInPoints((short) 14);
        headerFont.setColor(IndexedColors.RED.getIndex());

    // Create a CellStyle with the font
     CellStyle headerCellStyle = workbook.createCellStyle();
     headerCellStyle.setFont(headerFont);

    // Create a Row
     Row headerRow = sheet.createRow(0);
     System.out.println("");

    // Creating cells
     for(int i = 0; i < columns.length; i++)
     {
      Cell cell = headerRow.createCell(i);
      cell.setCellValue(columns[i]);
      cell.setCellStyle(headerCellStyle);
     }

     int rowCount = sheet.getLastRowNum();

    // FormulaEvaluator evaluator = workbook.getCreationHelper().createFormulaEvaluator();

    // CellReference cellReference = new CellReference("SUM(D2:E2:F2:G2:H2:I2)");
    // Row row = sheet.getRow(cellReference.getRow());
    // Cell cell = row.getCell(cellReference.getCol());
     int rowNum=1;
     int x=2;
     for(Class3 student1:stud1)
     {
     Row row = sheet.createRow(rowNum);

     row.createCell(0).setCellValue(student1.getS3Id());
     System.out.println(student1.getS3Id());
     row.createCell(1).setCellValue(student1.getStudentName());
    // CellValue cellValue = evaluator.evaluate(cell);
     row.createCell(2).setCellValue(student1.getStudentAge());

     row.createCell(3).setCellValue(student1.getEnglish());
     row.createCell(4).setCellValue(student1.getKannada());
     row.createCell(5).setCellValue(student1.getScience());
     row.createCell(6).setCellValue(student1.getMathematics());
     row.createCell(7).setCellValue(student1.getSocielSience());  
    // row.createCell(4, cellValue.getCellType());
     row.createCell(8).setCellValue(student1.getHindi());

     row.createCell(9).setCellFormula("SUM(D"+x+":E"+x+":F"+x+":G"+x+":H"+x+":I"+x+")");//.setCellValue(student1.getTotal());
     row.createCell(10).setCellFormula("((J"+x+")*100)/600");//student1.getPercentage());
     row.createCell(11).setCellValue(true);
     x++;
     rowNum++;
 }
 // Resize all columns to fit the content size
 for(int i = 0; i < columns.length; i++) {
     sheet.autoSizeColumn(i);
 }


 // Write the output to a file
///FileOutputStream fileOut = new FileOutputStream("excelone.xlsx");
String fileOut="C:/Users/Laxmi.Baragukar/Desktop/eclipse_neon/excelclass3.xlsx";

// return str;
//Base64.Encoder data=Base64.getEncoder().;
//String str=data.encodeToString(src)
 //String encode=fetching(fileOut);

 FileOutputStream fileOut1 = new FileOutputStream(fileOut);
 String encode=fetching(fileOut);
 workbook.write(fileOut1);
 fileOut1.close();
 workbook.close();


 //return fileOut;
}

I am pushing list of entity class objects from the postman.if i push Class1 entity object then it will check and generate Excel sheet for Class1 entity or if i push class2 entity object then it will check and generate Excel sheet for Class2 entity Object.

Answer 1

Please update your question. It contains too much code, most of it is not relevant for the question.

Generally, you cannot cast from LinkedHashMap to List (or vice versa). What you can do is this:

public static <V, K> void main(String[] args) {
    LinkedHashMap<K,V> map = new LinkedHashMap<K, V>();
    List<K> keyList = new ArrayList<>(map.keySet());
    List<V> valueList = new ArrayList<>(map.values());
}

(I'm not sure if that's what you are looking for. I didn't read all the code.)