Question

I have a Arraylist

List<?> myList=new ArrayList();

myList = fetchQuery(); //fetches the list of Entities

Now myList Has a list of Entities

Now i convert that list to string,so it is a string object now.

String temp=myList.toString();

My question is how to convert that temp string again to that myList(List of entities) ???

Any ideas??

My Temp Value looks like this

temp=”[entityObject1,entityObject2…….]” ..

i could not extract each object and cast it with that entity class.. is there a way??

Thanks..

Answer 1

I have done a sample program to do this conversion.
Things you have to be careful about.
1.The class whose list with which we will be working should have an
over ridden toString method.(You can have your own toString() format
but need to change the rest of implementation accordingly).

Sample content Object Class with over ridden toString() method.

class Sample {

    private String name;
    private String sex;

    @Override
    public String toString() {
        return "name=" + name + "&" + "sex=" + sex;
    }
    /**
     * @param name
     *            the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * @param sex
     *            the sex to set
     */
    public void setSex(String sex) {
        this.sex = sex;
    }

}

The Main Application.java

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

public class MainApplication {

    public static void main(String[] args) {
        List<Sample> e = new ArrayList<Sample>();
        Sample a1 = new Sample();
        a1.setName("foo1");
        a1.setSex("Male");

        Sample a2 = new Sample();
        a2.setName("foo2");
        a2.setSex("Male");
        e.add(a1);
        e.add(a2);

        String tmpString=e.toString();
        List<Sample> sampleList = (List<Sample>) chengeToObjectList(tmpString, Sample.class);
    }

    /**
     * Method to change String to List<Obj>.
     * @param listString
     * @param contentClass
     * @return List of Objects
     */
    public static Collection chengeToObjectList(String listString, Class contentClass) {

        Collection returnList = new ArrayList();

        // Code to remove [ and ] coming from the toString method
        if (listString.charAt(0) == '[') {
            listString = listString.substring(1);
        }
        if (listString.charAt(listString.length() - 1) == ']') {
            listString = listString.substring(0, listString.length() - 1);
        }

        String[] stringArray = listString.trim().split(",");
        for (int i = 0; i < stringArray.length; i++) {
            String[] contentArray = stringArray[i].trim().split("&");
            Object ob = null;
            try {
                ob = contentClass.newInstance();
            } catch (InstantiationException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            } catch (IllegalAccessException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            for (int j = 0; j < contentArray.length; j++) {

                String[] keyValueArray = contentArray[j].trim().split("=");

                String fieldName = keyValueArray[0].trim();
                //Code to make the 1st char uppercase
                String s = String.valueOf(fieldName.toCharArray()[0]);
                s = s.toUpperCase();
                fieldName = s + fieldName.substring(1);

                String fieldValue = keyValueArray[1].trim();

                Class[] paramTypes = new Class[1];
                paramTypes[0] = String.class;
                String methodName = "set" + fieldName; 
                Method m = null;
                try {
                    m = contentClass.getMethod(methodName, paramTypes);
                } catch (NoSuchMethodException m) {
                    m.printStackTrace();
                }
                try {
                    String result = (String) m.invoke(ob, fieldValue);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e1) {
                    e1.printStackTrace();
                }
            }
            returnList.add(ob);
        }

        return returnList;
    }
}