Hi all. I'm porting some javascript libraries to GWT and in this thread I
hope I can share and learn best ways of accessing Js native arrays from
java language.
I try to add the minimun overhead so I'm using GWT's JsArray, JsArrayMixed,
JsArrayString, etc for referencing arrays whenever I can. But this is not
so friendly for a Java programmer accustomed to work with real java arryas
(String[]) or with java.util.Collection API.
The first thing I thought of was convert js arrays to Java arrays.
Unfortunately i didn't found a way of doing this without (linear overhead);
public static JsArrayNumber toJsArrayDouble(double[]a) {
if(a==null)
return null;
JsArrayNumber jsa = (JsArrayNumber) JsArrayNumber.createArray();
for (int i = 0; i < a.length; i++) {
jsa.push(a[i]);
}
return jsa;
}
Now I'm experimenting on wrapping a Js Array into a java Collection. For
this I made a simple Java class that extends java.util.AbstractCollection
[0] and wrapps a pure js array. So from jsni code now I can return Java
Collections instead JsArray like types and the final user of my libs can
write java statements like for(String s : myOverlay.getArrayProp()) {..}.
Also this solution adds very few (constant) overhead. So now I'm using two
getters for js arrays, one that return the real js array object using GWT's
JsArray* and other that return a Java Collection:
/**
* Returns 'columns' property (JavaScript array)
* @return
*/
public native final JsArrayString columns() /*-{
return this["columns"];
}-*/;
/**
* Returns 'columns' property (Java Collection)
* @return
*/
public native final Collection<String> getColumns() /*-{
return
@org.sgx.test1.client.JsUtil::toJavaCollection(Lcom/google/gwt/core/client/JavaScriptObject;)(this["columns"]);
}-*/;
I would like to hear what others in the same situation do. Use JsArray*
GWT's classes vs more Java friendly API ??? Thanks in advance any
suggestion or comment is most appreciated.
[0] - Source code for my Java Collection class wrapper
import java.util.AbstractCollection;
import java.util.Iterator;
import com.google.gwt.core.client.JavaScriptObject;
/**
* a Java Friendly way of working with Js Arrays using the
Java.util.Collection API
* @author sg
*
* @param <T>
*/
public class JsArrayCollection<T> extends AbstractCollection<T> {
private JsArr<T> _data;
/**
* creates an empty array
*/
public JsArrayCollection() {
_data = JsArr.create().cast();
}
/**
* creates JsArrayCollection wrapping an existing js array
*/
public JsArrayCollection(JavaScriptObject data) {
this._data = data.cast();
}
public static <T> JsArrayCollection<T> create(JavaScriptObject data) {
return new JsArrayCollection<T>(data);
}
@Override
public Iterator<T> iterator() {
return new JsArrayIterator<T>(this);
}
@Override
public int size() {
return _data.size();
}
public static class JsArrayIterator<T> implements Iterator<T> {
private JsArrayCollection<T> arr;
int currentIndex;
public JsArrayIterator(JsArrayCollection<T> arr) {
this.arr = arr;
currentIndex=0;
}
@Override
public boolean hasNext() {
// System.out.println(currentIndex+" - "+arr.size());
return currentIndex < arr.size();
}
@Override
public T next() {
currentIndex++;
return arr._data.get(currentIndex-1);
}
@Override
public void remove() {
arr._data.slice(currentIndex-1, currentIndex);
}
}
/** untyped array */
private static class JsArr<T> extends JavaScriptObject {
protected JsArr(){}
public native final JsArr<T> slice(int start, int end)/*-{
return this.slice(start, end);
}-*/;
public static final native <T> JsArr<T> create() /*-{
return [];
}-*/;
public final native int size() /*-{
return this.length;
}-*/;
public final native T get(int i) /*-{
return this[i];
}-*/;
}
}
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