Releasing objects: minor fixes, add tests

DEVSIX-480

Author: Snipx

io/src/main/java/com/itextpdf/io/LogMessageConstant.java

@@ -20,6 +20,11 @@ public class LogMessageConstant {
      */
     public static final String FONT_HAS_INVALID_GLYPH = "Font {0} has invalid glyph: {1}";
 
+    /**
+     * Log message.
+     */
+    public static final String FORBID_RELEASE_IS_SET = "ForbidRelease flag is set and release is called. Releasing will not be performed.";
+
     /**
      * Log message.
      */

kernel/src/main/java/com/itextpdf/kernel/pdf/PdfIndirectReference.java

@@ -195,6 +195,12 @@ public String toString() {
         if (checkState(OriginalObjectStream)) {
             states.append("OriginalObjectStream; ");
         }
+        if (checkState(ForbidRelease)) {
+            states.append("ForbidRelease; ");
+        }
+        if (checkState(ReadOnly)) {
+            states.append("ReadOnly; ");
+        }
         return java.lang.String.format("%d %d R%s", getObjNumber(), getGenNumber(), states.substring(0, states.length() - 1));
     }
 

kernel/src/main/java/com/itextpdf/kernel/pdf/PdfObject.java

@@ -1,5 +1,6 @@
 package com.itextpdf.kernel.pdf;
 
+import com.itextpdf.io.LogMessageConstant;
 import com.itextpdf.kernel.PdfException;
 
 import java.io.IOException;
@@ -311,7 +312,7 @@ public void release() {
         // In case ForbidRelease flag is set, release will not be performed.
         if (checkState(ForbidRelease)) {
             Logger logger = LoggerFactory.getLogger(PdfObject.class);
-            logger.warn("ForbidRelease flag is set and release is called. Releasing will not be performed.");
+            logger.warn(LogMessageConstant.FORBID_RELEASE_IS_SET);
         } else {
             if (indirectReference != null && indirectReference.getReader() != null
                     && !indirectReference.checkState(Flushed)) {

kernel/src/main/java/com/itextpdf/kernel/pdf/PdfPage.java

@@ -308,7 +308,7 @@ public void flush() {
     }
 
     /**
-     * Flushes page and it's content stream. If <code>flushXObjects</code> is true the images and FormXObjects
+     * Flushes page and its content stream. If <code>flushXObjects</code> is true the images and FormXObjects
      * associated with this page will also be flushed.
      * <br>
      * For notes about tag structure flushing see {@link PdfPage#flush() PdfPage#flush() method}.

kernel/src/main/java/com/itextpdf/kernel/pdf/tagging/PdfStructElem.java

@@ -100,6 +100,7 @@ public class PdfStructElem extends PdfObjectWrapper<PdfDictionary> implements IP
     public PdfStructElem(PdfDictionary pdfObject) {
         super(pdfObject);
         ensureObjectIsAddedToDocument(pdfObject);
+        setForbidRelease();
         PdfName role = getPdfObject().getAsName(PdfName.S);
         type = identifyType(getDocument(), role);
     }