Github user martin-g commented on a diff in the pull request:
https://github.com/apache/wicket/pull/143#discussion_r46208533
--- Diff:
wicket-core/src/main/java/org/apache/wicket/markup/html/image/ExternalImage.java
---
@@ -0,0 +1,274 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.wicket.markup.html.image;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.wicket.markup.ComponentTag;
+import org.apache.wicket.markup.html.WebComponent;
+import org.apache.wicket.markup.html.image.Image.Cors;
+import org.apache.wicket.model.IModel;
+import org.apache.wicket.model.Model;
+
+/**
+ * A component to display external images. The src / srcset information
are hold in models
+ *
+ * @author Tobias Soloschenko
+ *
+ */
+public class ExternalImage extends WebComponent
+{
+
+ private static final long serialVersionUID = 1L;
+
+ /** The x values to be used within the srcset */
+ private List<String> xValues = null;
+
+ /** The sizes of the responsive images */
+ private List<String> sizes = null;
+
+ /**
+ * Cross origin settings
+ */
+ private Cors crossOrigin = null;
+
+ private IModel<?>[] srcSet;
+
+ /**
+ * Creates an external image
+ *
+ * @param id
+ * the component id
+ * @param src
+ * the source URL
+ * @param srcSet
+ * a list of URLs placed in the srcset attribute
+ */
+ public ExternalImage(String id, String src, String... srcSet)
+ {
+ this(id, src != null ? Model.of(src) : null,
convertToModel(srcSet));
+ }
+
+ /**
+ * Creates an external image
+ *
+ * @param id
+ * the component id
+ * @param src
+ * the model source URL
+ * @param srcSetModels
+ * a model list of URLs placed in the srcset attribute
+ */
+ public ExternalImage(String id, IModel<?> src, IModel<?>...
srcSetModels)
+ {
+ super(id, src);
+ this.srcSet = srcSetModels;
+ }
+
+ /**
+ * Converts a variable argument of Strings to an array of models
+ *
+ * @param srcSet
+ * a variable argument of URLs to be converted to an array
of models
+ * @return an array of models
+ */
+ private static IModel<?>[] convertToModel(String... srcSet)
+ {
+ IModel<?>[] models = null;
+ if (srcSet != null)
+ {
+
+ models = new IModel<?>[srcSet.length];
+ int i = 0;
+ for (String srcSetElement : srcSet)
+ {
+ models[i] = Model.of(srcSetElement);
+ i++;
+ }
+ }
+ else
+ {
+ models = new IModel<?>[0];
+ }
+ return models;
+ }
+
+ @Override
+ protected void onComponentTag(ComponentTag tag)
+ {
+ super.onComponentTag(tag);
+
+ if ("source".equals(tag.getName()))
+ {
+ buildSrcSetAttribute(tag, getSrcSet());
+ }
+ else
+ {
+ List<IModel<?>> srcSet = getSrcSet();
+ checkComponentTag(tag, "img");
+ buildSrcAttribute(tag, getDefaultModel());
+ if (srcSet.size() > 1)
+ {
+ buildSrcSetAttribute(tag, srcSet);
+ }
+ }
+
+ buildSizesAttribute(tag);
+
+ Cors crossOrigin = getCrossOrigin();
+ if (crossOrigin != null && Cors.NO_CORS != crossOrigin)
+ {
+ tag.put("crossOrigin", crossOrigin.getRealName());
+ }
+ }
+
+ /**
+ * Builds the src attribute
+ *
+ * @param tag
+ * the component tag
+ * @param srcModel
+ * the model containing the src URL
+ */
+ protected void buildSrcAttribute(final ComponentTag tag, IModel<?>
srcModel)
+ {
+ // The first model is the one put into src attribute
+ tag.put("src", srcModel.getObject().toString());
+ }
+
+ /**
+ * Builds the srcset attribute if multiple models are found as varargs
+ *
+ * @param tag
+ * the component tag
+ * @param srcSetModels
+ * the models containing the src set URLs
+ */
+ protected void buildSrcSetAttribute(final ComponentTag tag,
List<IModel<?>> srcSetModels)
+ {
+ int srcSetPosition = 0;
+ for (IModel<?> srcSetModel : srcSetModels)
+ {
+ String srcset = tag.getAttribute("srcset");
+ String xValue = "";
+
+ // If there are xValues set process them in the applied
order to the srcset attribute.
+ if (xValues != null)
+ {
+ xValue = xValues.size() > srcSetPosition &&
xValues.get(srcSetPosition) != null
+ ? " " + xValues.get(srcSetPosition) :
"";
+ }
+ tag.put("srcset",
+ (srcset != null ? srcset + ", " : "") +
srcSetModel.getObject() + xValue);
+ srcSetPosition++;
+ }
+ }
+
+ /**
+ * builds the sizes attribute of the img tag
+ *
+ * @param tag
+ * the component tag
+ */
+ protected void buildSizesAttribute(final ComponentTag tag)
+ {
+ // if no sizes have been set then don't build the attribute
+ if (sizes == null)
+ {
+ return;
+ }
+ String sizes = "";
+ for (String size : this.sizes)
+ {
+ sizes += size + ",";
+ }
+ int lastIndexOf = sizes.lastIndexOf(",");
+ if (lastIndexOf != -1)
+ {
+ sizes = sizes.substring(0, lastIndexOf);
+ }
+ if (!"".equals(sizes))
+ {
+ tag.put("sizes", sizes);
+ }
+ }
+
+ /**
+ * @param values
+ * the x values to be used in the srcset
+ */
+ public void setXValues(String... values)
+ {
+ if (xValues == null)
+ {
+ xValues = new ArrayList<>();
+ }
+ xValues.clear();
+ xValues.addAll(Arrays.asList(values));
+ }
+
+ /**
+ * @param sizes
+ * the sizes to be used in the size
+ */
+ public void setSizes(String... sizes)
+ {
+ if (this.sizes == null)
+ {
+ this.sizes = new ArrayList<>();
+ }
+ this.sizes.clear();
--- End diff --
could be in `else`
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