#51: PrettyPrintXMLWriter fails with a java.util.NoSuchElementException (Java 1.7 only)

src/main/java/org/codehaus/plexus/util/xml/PrettyPrintXMLWriter.java

@@ -304,7 +304,15 @@ public void endElement()
         {
             finishTag();
 
-            write( "</" + elementStack.removeLast() + ">" );
+            // see issue #51: https://github.com/codehaus-plexus/plexus-utils/issues/51
+            // Rationale: removed the element into a variable first, and only THEN
+            // concatenate the string.
+            // (this avoids the string concatenation optimization bug detected in Java 7)
+            // TODO: change the below code to a more efficient expression when the library
+            // be ready to target Java 8.
+            write( "</" );
+            write( elementStack.removeLast() );
+            write( ">" );
         }
 
         readyForNewLine = true;

src/test/java/org/codehaus/plexus/util/xml/PrettyPrintXMLWriterTest.java

@@ -16,7 +16,12 @@
  * limitations under the License.
  */
 
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStreamWriter;
 import java.io.StringWriter;
+import java.util.NoSuchElementException;
 
 import javax.swing.text.html.HTML.Tag;
 
@@ -28,6 +33,7 @@
  * Test of {@link PrettyPrintXMLWriter}
  *
  * @author <a href="mailto:vincent.siveton@gmail.com">Vincent Siveton</a>
+ * @author <a href="mailto:belingueres@gmail.com">Gabriel Belingueres</a>
  * @version $Id$
  */
 public class PrettyPrintXMLWriterTest
@@ -128,6 +134,75 @@ public void testEscapeXmlAttribute()
         assertEquals( "<div class=\"sect&#10;ion\"/>", w.toString() );
     }
 
+    public void testendElementAlreadyClosed()
+    {
+        try
+        {
+            writer.startElement( Tag.DIV.toString() );
+            writer.addAttribute( "class", "someattribute" );
+            writer.endElement(); // Tag.DIV closed
+            writer.endElement(); // Tag.DIV already closed, and there is no other outer tag!
+            fail( "Should throw a NoSuchElementException" );
+        }
+        catch ( NoSuchElementException e )
+        {
+            assert ( true );
+        }
+    }
+
+    /**
+     * Issue #51: https://github.com/codehaus-plexus/plexus-utils/issues/51
+     * 
+     * Purpose: test if concatenation string optimization bug is present.
+     * 
+     * Target environment: Java 7 (u79 and u80 verified) running on Windows.
+     * 
+     * Detection strategy: Tries to build a big XML file (~750MB size) and with 
+     * many nested tags to force the JVM to trigger the concatenation string 
+     * optimization bug that throws a NoSuchElementException when calling 
+     * endElement() method.
+     * 
+     * @throws IOException if an I/O error occurs
+     */
+    public void testIssue51DetectJava7ConcatenationBug()
+        throws IOException
+    {
+        File dir = new File( "target/test-xml" );
+        if ( !dir.exists() )
+        {
+            assertTrue( "cannot create directory test-xml", dir.mkdir() );
+        }
+        File xmlFile = new File( dir, "test-issue-51.xml" );
+        OutputStreamWriter osw = new OutputStreamWriter( new FileOutputStream( xmlFile ), "UTF-8" );
+        writer = new PrettyPrintXMLWriter( osw );
+
+        int iterations = 20000;
+
+        try
+        {
+            for ( int i = 0; i < iterations; ++i )
+            {
+                writer.startElement( Tag.DIV.toString() + i );
+                writer.addAttribute( "class", "someattribute" );
+            }
+            for ( int i = 0; i < iterations; ++i )
+            {
+                writer.endElement(); // closes Tag.DIV + i
+            }
+        }
+        catch ( NoSuchElementException e )
+        {
+            fail( "Should not throw a NoSuchElementException" );
+        }
+        finally
+        {
+            if ( osw != null )
+            {
+                osw.close();
+            }
+        }
+    }
+
     private void writeXhtmlHead( XMLWriter writer )
     {
         writer.startElement( Tag.HEAD.toString() );