Empty entry in ElementList SimpleXML

问题:

my question is simple, but I can't find nothing about it.

I Have a list class and an entry class for XML Serialization:

@Root(name = "entries")
public class List {

    @ElementList(required = false, entry = "entry", inline = true, empty = true)
    private List<Entry> entries;
}

@Root
public class Entry {

    @Element(name = "entry_id", required = true)
    private long id;

    @Element(name = "text", required = true)
    private String Text;
}

I'm trying to parse this XML, which don't have any entries in the list:

<entries>
   <entry />
<entries>

The follow error is returned:

W/System.err(3335): org.simpleframework.xml.core.ValueRequiredException: Unable to satisfy @org.simpleframework.xml.Element(data=false, name=entry_id, required=true, type=void) on field 'id' private long com.android.apps.model.Entry.id for class com.android.apps.model.Entry at line 2

What am I doing wrong? The ElementList is set empty = true and required = false. anybody can help?

回答1:

You can check for empty elements manually:

@Root(name = "entries")
@Convert(List.ListConverter.class) // Set the converter
public class List
{
    @ElementList(required = false, entry = "entry", inline = true, empty = true)
    private java.util.List<Entry> entries;


    public void add(Entry e)
    {
        // Just for testing
        entries.add(e);
    }



    static class ListConverter implements Converter<List>
    {
        @Override
        public List read(InputNode node) throws Exception
        {
            List l = new List();
            InputNode child = node.getNext("entry");

            while( child != null)
            {
                if( child.isEmpty() == true ) // child is an empty tag
                {
                    // Do something if entry is empty
                }
                else // child is not empty
                {
                    Entry e = new Persister().read(Entry.class, child); // Let the Serializer read the Object
                    l.add(e);
                }

                child = node.getNext("entry");
            }

            return l;
        }


        @Override
        public void write(OutputNode node, List value) throws Exception
        {
            // Not required for reading ...
            throw new UnsupportedOperationException("Not supported yet.");
        }
    }
}

How to use:

Serializer ser = new Persister(new AnnotationStrategy()); // Set AnnotationStrategy here!
List l = ser.read(List.class, yourSourceHere);

Documentation:

• Converter
• AnnotationStrategy

回答2:

To avoid the error in parse do one should place annotation tags @set e @get

@Root(name = "entries", strict = false)
public class List {

@set:ElementList(required = false, entry = "entry", inline = true, empty = true)
@get:ElementList(required = false, entry = "entry", inline = true, empty = true)
    private List<Entry> entries;

}

@Root
public class Entry {

    @set:Element(name = "entry_id", required = true)
    @get:Element(name = "entry_id", required = true)
    private long id;

    @set:Element(name = "text", required = true)
    @get:Element(name = "text", required = true)
    private String Text;
}