在 Java 中存储多个列表的最佳方式是什么？

Question

I am extracting data using some xyz logic. After extraction I am getting multiple list in each iteration.

   for (int i= 0; i<= 5; i++) 
   {
          for (int j= 0; j<= 5; j++) 
          {
              //data extraction logic
             lList1.add(value1);
             lList2.add(value2);
             lList3.add(value3);
          }
         //in each iteration I am getting list different 
          System.out.println(" lList1 for iteration "+i+"is: "+lList1);
          System.out.println(" lList2 for iteration "+i+"is: "+lList2);
          System.out.println(" lList3 for iteration "+i+"is: "+lList3);
   }

I need to pass these list to database. Each list is associated with one column in db.
Example: lList1 is for column1, lList2 is for column2, lList3 is for column3 etc

What is best way to pass these list to db or to write these values row by row in java output should be like

row 1 lList1 lList2 lList3 etc of first iteration list values
row 2 lList1 lList2 lList3 etc of second iteration list values etc

Can anyone help?

Answer 1

You can use Multidimensional Collections

ArrayList<ArrayList<Object>> a = new ArrayList<ArrayList<Object>>();

Result can be like that (based on your logic):

Multidimensional ArrayList: [[3, 4], [12, 13], [22, 23], [33,23]]

here is a full example:

ArrayList<ArrayList<Object>> list = new ArrayList<ArrayList<Object>>(); 
for (int i= 0; i<= 5; i++) {
    //if you got all the values 
    list.add(new ArrayList<Object>(Arrays.asList(value1, value2, value3))); 
    //else you have to fetch them from another loop
   for (int j= 0; j<= 5; j++) {
            list.add(new ArrayList<Object>()); 
            list.get(j).add(value1); 
          }
   }

Answer 2

Create a class which will contain three members col1,col2 and col3 and make list of that class and use it.

class MyRow
{
public {col1datatype} col1;
public {col2DataType} col2;
public {col3DataType} col3;
}

---

your function

 List<MyRow> lstRows = new ArrayList<MyRow>();

         for (int i= 0; i<= 5; i++) 
           {
                  for (int j= 0; j<= 5; j++) 
                  {
                    MyRow row = new MyRow(); 
                     row.col1 = value1;
                     row.col2 = value2;
                     row.col3 = value3;
                     llstRows.Add(row); 
                  }
            }

And use that lstRows accordingly at database transaction.

Answer 3

I would suggest the following flow:

• First of all check the size of each listing and take the size of the biggest listing present, lets say its lList3 with 10 elements in it.
• Make sure that your columns in DB are nullable meaning they can be NULL
• Make a for loop to run 10 times (length of the biggest list) and insert lList1[i], lList2[i] and lList3[i] to the DB in each loop. Of course you will need to check first if the current index exists in the list, if not then insert NULL for that list column.

This way you will have each row in DB, the same way you need to list them out later in your front end. Also it will be easier to do any data search.

Answer 4

I would suggest in that case to serialize it to Json and store it in the column (since you use this approach with columns for lists).

When retrieving data from the DB, you can just deserialize it from Json to a List object.

For example Entity Framework is doing the same in .NET

Answer 5

if all list contains same length then make one common function for all ArrayList and iterate it with the loop of the maximum size ArrayList: It should be like: for(int i=0;i<lList1.size();i++) { String insertQueryMainProduct = "INSERT INTO " + "" + tableName + "" + "(ColumnOneName,ColumnSecondName,ColumnThirdName)" + " VALUES('" +lList1.get(i)+ "', '" + lList2.get(i)+ "', '" + lList3.get(i)+ "')"; System.out.println("Query: " + insertQueryMainProduct); statement.executeUpdate(insertQueryMainProduct); for(int i=0;i<lList1.size();i++) { String insertQueryMainProduct = "INSERT INTO " + "" + tableName + "" + "(ColumnOneName,ColumnSecondName,ColumnThirdName)" + " VALUES('" +lList1.get(i)+ "', '" + lList2.get(i)+ "', '" + lList3.get(i)+ "')"; System.out.println("Query: " + insertQueryMainProduct); statement.executeUpdate(insertQueryMainProduct); Hope this will help you