Passing a list as a parameter to ModelAndView

[escapee]

I was wondering if anyone knows how to pass a list of model objects as a parameter to the ModelandView method in the controller. For example, if i want to get a list of all employees working in a company, then passing the company Id in the URL i should search for employees working in that company, put it in a list of employee object and then the return statement of the method being something like

return new ModelAndView(XML_VIEW_NAME, "employees", emps); where emps is a List<Employee> and Employee is a POJO.

It gives an error

java.lang.OutOfMemoryError: Java heap space


pointing to emps.add(emp) where emp is the Employee object at the controller code.

I am deploying the app on Google App Engine. The actual code I am working on is getting a list of 'variables' in an 'application' in the form of an XML in stead of a list of employees in a company.

Thanks

[dr_pompeii]

Can you post your code?

About this

It gives an error
java.lang.OutOfMemoryError: Java heap space

How are you filling the collection? from the DB?
how many POJO would contain your collection?
If is really high it could be a reason of the exception

[escapee]

CONTROLLER
----------

import java.io.IOException;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.List;

import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;

import org.springframework.oxm.XmlMappingException;
import org.springframework.oxm.castor.CastorMarshaller;
//import org.springframework.oxm.jaxb.Jaxb2Marshaller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariab le;
import org.springframework.web.bind.annotation.RequestBod y;
import org.springframework.web.bind.annotation.RequestMap ping;
import org.springframework.web.bind.annotation.RequestMet hod;
import org.springframework.web.servlet.ModelAndView;

import com.google.appengine.api.datastore.DatastoreServic e;
import com.google.appengine.api.datastore.DatastoreServic eFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.EntityNotFoundE xception;
import com.google.appengine.api.datastore.FetchOptions;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.appengine.api.datastore.Query;
import com.google.appengine.api.datastore.Query.FilterOpe rator;
import com.example.bean.Application;
import com.example.bean.Variable;


import java.util.logging.Logger;

@Controller
public class DataController {

private CastorMarshaller castorMarshaller;

public void setCastorMarshaller(CastorMarshaller castorMashaller) {
this.castorMarshaller = castorMashaller;
}

private static final String XML_VIEW_NAME = "rest";


@RequestMapping(method=RequestMethod.GET, value="/application/{id}")
public ModelAndView getVariables(@PathVariable String id) throws Exception {
Query findAttsQuery = new Query("Variable");
id = id.substring(0, id.lastIndexOf('.'));

findAttsQuery.addFilter("Application", FilterOperator.EQUAL, id);

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
List<Entity> results = datastore.prepare(findAttsQuery).asList(FetchOptio ns.Builder.withDefaults());
int i =0;

ArrayList<Variable> vars = new ArrayList<Variable>(results.size());
ModelAndView mav = new ModelAndView();

while(i<results.size()) {
vars.add(new Variable(results.get(i).getKey().getName(),results .get(i).getProperty("Type").toString(),results.get (i).getProperty("Value").toString()));
mav.addObject("variable", vars);

}

mav.setViewName(XML_VIEW_NAME);
return mav;
}


Here goes the code. I have modified it a little using a modelandview object defined. This code retrieves data from hte google app engine datastore.

The issue I have realized is in the vars.add() statement . When I just create 2 different Variable objects (as I know there are only 2 objects in teh database for a particular search query of GET.) and add those 2 objects to the array list vars , it works perfectly fine.

I am pretty new to Spring and Java and am wondering in second thoughts if this is a Java error am doing here.

Here is the bean:Variable
---------------------

public class Variable {

private String id;
private String value;

private String type;

public Variable() {}

public Variable(String id, String value, String type) {
this.id = id;
this.value = value;
this.type = type;

}
public String getId() {
return id;
}

public void setId(String id) {
this.id = id;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}

public String getType() {
return type;
}

public void setType(String type) {
this.type = type;
}


}
mapping .xml for marshaller

<class name="com.example.bean.Variable" identity="id">
<map-to xml="variable" />
<field name="id" type="string">
<bind-xml name="id" node="element" />
</field>
<field name="value" type="string">
<bind-xml name="value" node="element" />
</field>
<field name="type" type="string">
<bind-xml name="type" node="element" />
</field>
</class>


Thank you!

[escapee]

mav.addObject("variable", vars); should be outside the loop. I moved it out but still the error.

[dr_pompeii]

Use code tags, is more readable for us

About this

findAttsQuery.addFilter("Application", FilterOperator.EQUAL, id);

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
List<Entity> results = datastore.prepare(findAttsQuery).asList(FetchOptio ns.Builder.withDefaults());
int i =0;

ArrayList<Variable> vars = new ArrayList<Variable>(results.size());
ModelAndView mav = new ModelAndView();

while(i<results.size()) {
vars.add(new Variable(results.get(i).getKey().getName(),results .get(i).getProperty("Type").toString(),results.get (i).getProperty("Value").toString()));
mav.addObject("variable", vars);

How was filled the bold part? and how many elements are in your collection?

mav.addObject("variable", vars); 
should be outside the loop. I moved it out but still the error.

OK

[escapee]

The bold statement populates the List using Google App Engine's low level API.
Right now in my datastore there are 2 elements (or entities, in GAE objects are stored as entities having key value pairs). But it will not be limited to 2 elements and hence should iterate over the list.

Thank you.

[escapee]

Hi

It works now! I am sorry for all the noise!

@RequestMapping(method=RequestMethod.GET, value="/application/{id}")
	public ModelAndView getVariables(@PathVariable String id) throws Exception {
		Query findAttsQuery = new Query("Variable");
		id = id.substring(0, id.lastIndexOf('.'));
		
		findAttsQuery.addFilter("Application", FilterOperator.EQUAL, id);
		DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
		List<Entity> results = datastore.prepare(findAttsQuery).asList(FetchOptions.Builder.withDefaults());

		
		ArrayList<Variable> vars = new ArrayList<Variable>(results.size());
		ModelAndView mav = new ModelAndView();
		Iterator<Entity> it = results.iterator ();
		while (it.hasNext ()) {
		    Entity ent =  it.next ();
		
		Variable var = new Variable();
		
		var.setId(ent.getKey().getName());
		if (ent.getProperty("Type") == null)
			var.setType("NULL");
		else
		var.setType(ent.getProperty("Type").toString());
		
		if (ent.getProperty("Value") == null)
			var.setValue("NULL");
		else
		var.setValue(ent.getProperty("Value").toString()); 
		vars.add(var);
		}
		
		mav.addObject("variable", vars);	
	mav.setViewName(XML_VIEW_NAME);
		return mav;
	}

[dr_pompeii]

It works now! I am sorry for all the noise!

Don't worry

it seems the key line was

while(i<results.size()) {
vars.add(new Variable(results.get(i).getKey().getName(),results .get(i).getProperty("Type").toString(),results.get (i).getProperty("Value").toString()));
mav.addObject("variable", vars);
}

which was re edited to

while (it.hasNext ()) {
		    Entity ent =  it.next ();
		
		Variable var = new Variable();
		
		var.setId(ent.getKey().getName());
		if (ent.getProperty("Type") == null)
			var.setType("NULL");
		else
		var.setType(ent.getProperty("Type").toString());
		
		if (ent.getProperty("Value") == null)
			var.setValue("NULL");
		else
		var.setValue(ent.getProperty("Value").toString()); 
		vars.add(var);
		}