如何将结果集复制到对象中？[英] How to copy resultset into object?

问题描述

I am using the following to add retrieved values to the class. all values will be added to attributes of the class but I am using compisition ( have an object of class in the class) and it does not show anything on output.

class employee 
{
....
private Address address = new Address();
.....
}
 ...
Employee emp = new Employee();
        try {

            ps = con.prepareStatement("select * from employee,address "
                    + "WHERE employee.username = ? AND "
                    + "employee.ADD_ID = address.ID");

            ps.setString(1, username);
            ResultSet r = ps.executeQuery();
            if (r.next()) {

                BeanProcessor bp = new BeanProcessor();
                emp = bp.toBean(r,Employee.class);
                System.out.println("blockkkk:"+emp.getAddress().getBlock());  
                                            //output of above line is blockkkk:null
            }

            con.close();
            ps.close();
        } catch (SQLException e) {
            System.err.println(e.getMessage());

        }
       return emp;

Address class is as following:

  public class Address {
    .....
    private String block;
    ....
      public String getBlock() {
            return block;
        }

        public void setBlock(String block) {
            this.block = block;
        }
    ....
   }

推荐答案

The BeanProcessor.toBean works like this:

Convert a ResultSet row into a JavaBean. This implementation uses reflection and BeanInfo classes to match column names to bean property names. Properties are matched to columns based on several factors:

• The class has a writable property with the same name as a column. The name comparison is case insensitive.
• The column type can be converted to the property's set method parameter type with a ResultSet.get* method. If the conversion fails (ie. the property was an int and the column was a Timestamp) an SQLException is thrown.

Primitive bean properties are set to their defaults when SQL NULL is returned from the ResultSet. Numeric fields are set to 0 and booleans are set to false. Object bean properties are set to null when SQL NULL is returned. This is the same behavior as the ResultSet get* methods.

May be the address is not a writable property. Pls do check it.

其他推荐答案

 public static Object copyFromResultSet(Class clazz, ResultSet resultSet)
{
    ArrayList objectArrayList = new ArrayList(1);
    try
    {
        Object object = clazz.newInstance();
        objectArrayList.add(object);
        copyFromResultSet(objectArrayList, resultSet);
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    return objectArrayList.get(0);
}     

then:

public static void copyFromResultSet(ArrayList<Object> objectArrayList, ResultSet resultSet)
{
    ArrayList arrayList = null;
    try
    {
        if (objectArrayList != null)
        {
            int objectArrayList_len = objectArrayList.size();
            int objectArrayList_index = 0;
            java.beans.BeanInfo toBeanInfo[] = new java.beans.BeanInfo[objectArrayList_len];

            Vector<Method> objectMethodVector[] = new Vector[objectArrayList_len];
            Vector<Type> objectTypeVector[] = new Vector[objectArrayList_len];
            int totalMethod[] = new int[objectArrayList_len];
            int[][] indexes = new int[objectArrayList_len][];

            for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
            {
                toBeanInfo[objectArrayList_index] = java.beans.Introspector.getBeanInfo(objectArrayList.get(objectArrayList_index).getClass());
            }
            if (objectArrayList_len > 0 && resultSet != null)
            {
                Method method = null;
                Type type[] = null;
                int cols = 0;
                String colName = null;
                for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
                {
                    //toBeanInfo[objectArrayList_index]=java.beans.Introspector.getBeanInfo(objectArrayList.get(objectArrayList_index).getClass());
                    java.beans.PropertyDescriptor toPropertyDescriptor[] = toBeanInfo[objectArrayList_index].getPropertyDescriptors();
                    int toPropertyDescriptor_length = toPropertyDescriptor.length;
                    method = null;
                    type = null;

                    ResultSetMetaData resultSetMetaData = resultSet.getMetaData();

                    cols = resultSetMetaData.getColumnCount();
                    colName = null;

                    Vector<Method> methodVector = new Vector(cols);
                    Vector<Type> typeVector = new Vector(cols);

                    indexes[objectArrayList_index] = new int[cols];
                    totalMethod[objectArrayList_index] = -1;
                    for (int i = 1; i <= cols; i++)
                    {
                        colName = resultSetMetaData.getColumnName(i);
                        for (int j = 0; j < toPropertyDescriptor_length; j++)
                        {
                            if (toPropertyDescriptor[j].getName().equalsIgnoreCase(colName))
                            {
                                totalMethod[objectArrayList_index]++;
                                method = toPropertyDescriptor[j].getWriteMethod();
                                type = method.getGenericParameterTypes();
                                methodVector.add(method);
                                typeVector.add(type[0]);
                                indexes[objectArrayList_index][totalMethod[objectArrayList_index]] = i;
                                break;
                            }
                        }
                    }
                    objectMethodVector[objectArrayList_index] = (methodVector);
                    objectTypeVector[objectArrayList_index] = (typeVector);
                }

                if (resultSet.next())
                {
                    arrayList = new ArrayList();
                    for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
                    {
                        for (int i = 0; i <= totalMethod[objectArrayList_index]; i++)
                        {
                            //System.out.println(objectMethodVector[objectArrayList_index].get(i));
                            objectMethodVector[objectArrayList_index].get(i).invoke(objectArrayList.get(objectArrayList_index), getObject(indexes[objectArrayList_index][i], objectTypeVector[objectArrayList_index].get(i), resultSet));
                        }
                        arrayList.add(objectArrayList.get(objectArrayList_index));
                    }
                }
                while (resultSet.next())
                {
                    for (objectArrayList_index = 0; objectArrayList_index < objectArrayList_len; objectArrayList_index++)
                    {
                        for (int i = 0; i <= totalMethod[objectArrayList_index]; i++)
                        {
                            objectMethodVector[objectArrayList_index].get(i).invoke(objectArrayList.get(objectArrayList_index), getObject(indexes[objectArrayList_index][i], objectTypeVector[objectArrayList_index].get(i), resultSet));
                        }
                        arrayList.add(objectArrayList.get(objectArrayList_index));
                    }
                }
            }
        }
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
} 

just copy paste this code call method copyFromResultSet(class, ResultSet ) pass two perameters first is class name and second is resultset.

i am sure this is working properlly