PDFBOX-5943: add a method to remove all page resources from the cache

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1923474 13f79535-47bb-0310-9956-ffa450edef68

Author: lehmi

pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDPage.java

@@ -20,6 +20,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -46,6 +47,8 @@
 import org.apache.pdfbox.pdmodel.common.PDMetadata;
 import org.apache.pdfbox.pdmodel.common.PDRectangle;
 import org.apache.pdfbox.pdmodel.common.PDStream;
+import org.apache.pdfbox.pdmodel.graphics.PDXObject;
+import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
 import org.apache.pdfbox.pdmodel.interactive.action.PDPageAdditionalActions;
 import org.apache.pdfbox.pdmodel.interactive.annotation.AnnotationFilter;
 import org.apache.pdfbox.pdmodel.interactive.annotation.PDAnnotation;
@@ -114,6 +117,64 @@ public PDPage(COSDictionary pageDictionary)
         this.resourceCache = resourceCache;
     }
 
+    /**
+     * Remove all page resources from the cache to avoid relying on the implementation of the Cache. Does make sense
+     * after processing a page.
+     */
+    public void removePageResourceFromCache()
+    {
+        if (resourceCache == null)
+        {
+            return;
+        }
+        // limit purge operation to page resources, don't remove inherited resources
+        removeResources(page.getCOSDictionary(COSName.RESOURCES));
+    }
+
+    private void removeResources(COSDictionary resources)
+    {
+        if (resources == null)
+        {
+            return;
+        }
+        getIndirectResourceObjects(resources, COSName.COLORSPACE)
+                .forEach(resourceCache::removeColorSpace);
+        getIndirectResourceObjects(resources, COSName.EXT_G_STATE)
+                .forEach(resourceCache::removeExtState);
+        getIndirectResourceObjects(resources, COSName.FONT)
+                .forEach(resourceCache::removeFont);
+        getIndirectResourceObjects(resources, COSName.PATTERN)
+                .forEach(resourceCache::removePattern);
+        getIndirectResourceObjects(resources, COSName.PROPERTIES)
+                .forEach(resourceCache::removeProperties);
+        getIndirectResourceObjects(resources, COSName.SHADING)
+                .forEach(resourceCache::removeShading);
+        for (COSObject cosObject : getIndirectResourceObjects(resources, COSName.XOBJECT))
+        {
+            PDXObject removedXObject = resourceCache.removeXObject(cosObject);
+            // clean up the resources of the XFormObject
+            if (removedXObject instanceof PDFormXObject)
+            {
+                COSStream cosStream = removedXObject.getCOSObject();
+                removeResources(cosStream.getCOSDictionary(COSName.RESOURCES));
+            }
+        }
+    }
+
+    private List<COSObject> getIndirectResourceObjects(COSDictionary pageResources, COSName kind)
+    {
+        COSDictionary resourcesDictionary = pageResources.getCOSDictionary(kind);
+        if (resourcesDictionary == null)
+        {
+            return Collections.emptyList();
+        }
+        return resourcesDictionary.getValues().stream() //
+                .filter(f -> f instanceof COSObject) //
+                .map(f -> (COSObject) f) //
+                .filter(COSObject::isDereferenced) //
+                .collect(Collectors.toList());
+    }
+
     /**
      * Convert this standard java object to a COS object.
      *