Manually add data to a Java ResultSet

问题:

I'm not sure if this might be a rather stupid question. But is it possible to manually add data/values into a java resultset? For instance if I already have an existing populated ResultSet, is there a way to add more data ontop of it?

//if this was possible for instance
ResultSet rs;
rs.setData("someValue");

Thanks!

回答1:

You can wrap any JDBC ResultSet with your custom implementation:

public class MyResultSet implements ResultSet {

  // Delegate most implementations to the underlying database result set:
  private final ResultSet delegate;
  public MyResultSet(ResultSet delegate) {
    this.delegate = delegate;
  }

  @Override
  public int getInt(int index) throws SQLException {
    return delegate.getInt(index);
  }

  // [... more delegate methods ...]

  // Add custom methods
  public void setData(Object someValue) { ... }
  public Object getData() { ... }
}

Your custom result set behaves like any other result set. Client code reading data from your custom result set will be oblivious of the changes you perform to it "under the hood". In other words, you can pretend that some data is available

public class MyResultSet implements ResultSet {
  // [...]

  @Override
  public int getInt(int index) throws SQLException {
    if (index == 3) {
      return 42;
    } else {
      return delegate.getInt(index);
    }
  }
}

回答2:

You can add values to a ResultSet using insertRow() but this will also add the data to the underlying database. If you wanted to do this you'd do something like:

rs.moveToInsertRow();
rs.updateString("someColumn", "someValue");
rs.insertRow();

If you just want to add data to the results without modifying the database add the data from the ResultSet to a List or Set or something similar and modify that.

回答3:

You need to create a statement that will return updatable ResultSet. Example:

  Statement stmt = connection.createStatement(
     ResultSet.TYPE_SCROLL_SENSITIVE, 
     ResultSet.CONCUR_UPDATABLE
  );
  ResultSet resultSet = stmt.executeQuery(" SELECT col1 FROM tablename ");
  rs.absolute(5); // moves the cursor to the 5th row of rs
  rs.updateString("col1", "NEW VALUE"); // updates the col1 column of row 5 to be NEW VALUE
  rs.updateRow(); // updates the row in the data source