Set HashMap Objects using Streams

[vivek dhiman]

Hi,

I have the below code as per the traditional way to iterate and set the object value in hashmap as follows.

 
            final Iterator<Page> childPages = currentPage.listChildren();
            String description = "";
            while (childPages.hasNext()) {
                obj = new HashMap<String, Object>();
                final Page childPage = childPages.next();
                final String title = childPage.getTitle().toString();
                final String path = childPage.getPath().toString();
                obj.put(TITLE, title);
                obj.put(SRC, path + HTML_EXTENSION);
                obj.put(ACTIVE, false);
                description = childPage.getContentResource().getValueMap().get("jcr:description", "");
                obj.put(CONTENT, description);
                listModel.add(obj);
            }

Same i want to use with Streams/Lamdas. Below is what I tried which is incomplete. Can someone help in that.

        final Iterable<Page> iterable = () -> childPages;
        final Stream<Page> targetStream = StreamSupport.stream(iterable.spliterator(), false);
        targetStream.forEach((page) -> {
            obj.put("title", page.getTitle());
            obj.put("src", page.getPath()+HTML_EXTENSION);
            obj.put("active", false);
            obj.put("content", page.getContentResource().getValueMap().get("jcr:description", ""));
            listModel.add(obj);
        });

But its adding same object multiple times. Where i as doing wrong. I don't want to initialize the obj inside stream.

[Knute Snortum]

Hi. I formatted the code a bit and moved the discussion to the Java 8 forum.

I'm not sure you need a spliterator, which is used to with multiple threads, but I'll leave that to the more knowledgeable.

[Carey Brown]

I'm a total noob when it comes to Java8 but I thought I'd take a stab at it. Please feel free to shoot holes in this.

public class Page
{
	private String			title;
	private String			path;
	private boolean			active;
	private String			content;
	
	public Page( String title, String path, boolean active, String content )
	{
		this.title = title;
		this.path = path;
		this.active = active;
		this.content = content;
	}

	public String getTitle()	{	return title;	}
	public String getPath()		{	return path;	}
	public boolean isActive()	{	return active;	}
	public String getContent()	{	return content;	}
}

import java.util.HashMap;

@SuppressWarnings("serial")
public class PageMap extends HashMap<String,Object>
{
	public PageMap( Page page )
	{
        put("title", page.getTitle());
        put("src", page.getPath()+".html");
        put("active", false);
        put("content", page.getContent() );
	}
}

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class Main
{
	public static void main( String[] args )
	{
		List<Page>		pageList = new ArrayList<>();
		
		// init with dummy values
		for( int i=0 ; i < 10 ; i++ )
			pageList.add( new Page( Integer.toString(i), "path", false, "content" ) );
		
		List<PageMap>	list = pageList.stream()
				.map( page -> new PageMap( page ) )
				.collect( Collectors.toList() );
	}
}

[Stephan van Hulst]

Carey, you can use a method reference instead:

List<PageMap> list = pageList.stream()
  .map(PageMap::new)
  .collect(Collectors.toList());

[Carey Brown]

Thank you. Forgot about that.

[Campbell Ritchie]

What about groupingBy?

[Stephan van Hulst]

I'm not sure if groupingBy() is convenient in this case, because it will result in a mapping to lists, not a list of maps.

[Campbell Ritchie]

Agree. I obviously didn't read it proberly. If you want a List<Map<Something>> groupingBy won't work.