类型转换为什么出错？数据库中就是int

public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
if(e.getSource()==jb1)
{
rs = ct.getResult("select * from Book");

        int rowCount = -1;              
            try {
                //ResultSetMetaData data=rs.getMetaData();
                //int colNum=data.getColumnCount();
                while(rs.next()) {
                    rowCount++;
                    }
            //  System.out.println(rowCount);
                    for(int i=0;i<=rowCount;i++)
                        ct.updateSql("update Book set Book_id = '"+jt.getValueAt(i, 0)+
                        "',Book_name = '"+jt.getValueAt(i, 1)+
                        "',Book_publishment = '" +jt.getValueAt(i, 2)+
                        "',Book_price = " +jt.getValueAt(i, 3)+
                        ",Book_type = '" +jt.getValueAt(i, 4)+
                        "',Book_num = " +jt.getValueAt(i, 5)+
                        ",Book_Writer = '" +jt.getValueAt(i, 6)+
                        "',Book_inlib = "+jt.getValueAt(i, 7)+
                        " where Book_id='"+jt.getValueAt(i, 0)+"'");    
                    JOptionPane.showMessageDialog(null, "数据已更改", "提示",JOptionPane.WARNING_MESSAGE);
                System.out.println(jt.getValueAt(rowCount, 0));
                    if(jt.getValueAt(rowCount+1, 0)!=null)
                    {
                        System.out.print("这里面有数据，正打算插入");
                        ct.updateSql("insert into Book values('"+jt.getValueAt(rowCount+1, 0)+"','"
                        +jt.getValueAt(rowCount+1, 1)+"','"
                        +jt.getValueAt(rowCount+1, 2)+"','"
                        +jt.getValueAt(rowCount+1, 3)+"','"
                        +jt.getValueAt(rowCount+1, 4)+"','"
                        +jt.getValueAt(rowCount+1, 5)+"','"
                        +jt.getValueAt(rowCount+1, 6)+"','"
                        +jt.getValueAt(rowCount+1, 7)+
                        "')");

jt.getValueAt(rowCount+1, 7)--第八个元素插入出错
com.microsoft.sqlserver.jdbc.SQLServerException: 在将 varchar 值 'null' 转换成数据类型 int 时失败。

数据里面有null空值，在调用sql以前先加上判断

标题说“数据库中就是int”，但是报错确是“ 在将 varchar 值 'null'……”，这本身就有问题……

可以直接通过三目运算符在插入之前判断一下