diff --git a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFSimpleShape.java b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFSimpleShape.java
index 9cab106a140..bc60130c764 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFSimpleShape.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFSimpleShape.java
@@ -398,14 +398,15 @@ private String getBulletPrefix(ListAutoNumber scheme, int value) {
      * Convert an integer to its alpha equivalent e.g. 1 = A, 2 = B, 27 = AA etc
      */
     private String valueToAlpha(int value) {
-        String alpha = "";
+        StringBuilder alpha = new StringBuilder();
         int modulo;
         while (value > 0) {
             modulo = (value - 1) % 26;
-            alpha = (char) (65 + modulo) + alpha;
+            alpha.append((char) (65 + modulo));
             value = (value - modulo) / 26;
         }
-        return alpha;
+        alpha.reverse();
+        return alpha.toString();
     }
 
     private static String[] _romanChars = new String[] { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V",
diff --git a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/helpers/XSSFXmlColumnPr.java b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/helpers/XSSFXmlColumnPr.java
index 2fdd7fa06d2..70ee324c629 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/helpers/XSSFXmlColumnPr.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/helpers/XSSFXmlColumnPr.java
@@ -78,7 +78,7 @@ public String getLocalXPath() {
 
         String[] xPathTokens = ctXmlColumnPr.getXpath().split("/");
         for (int i = numberOfCommonXPathAxis; i < xPathTokens.length; i++) {
-            localXPath.append("/" + xPathTokens[i]);
+            localXPath.append("/").append(xPathTokens[i]);
         }
         return localXPath.toString();
     }
diff --git a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Chunk.java b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Chunk.java
index 5073771fc32..43d2fb65ea6 100644
--- a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Chunk.java
+++ b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Chunk.java
@@ -23,6 +23,7 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import java.util.Locale;
 
 import org.apache.poi.hsmf.datatypes.Types.MAPIType;
+import org.apache.poi.util.StringUtil;
 
 public abstract class Chunk {
     public static final String DEFAULT_NAME_PREFIX = "__substg1.0_";
@@ -62,13 +63,14 @@ public MAPIType getType() {
     public String getEntryName() {
         String type = this.type.asFileEnding();
 
-        String chunkId = Integer.toHexString(this.chunkId);
-        while (chunkId.length() < 4) {
-            chunkId = "0" + chunkId;
+        StringBuilder chunkId = new StringBuilder(Integer.toHexString(this.chunkId));
+        int need0count = 4 - chunkId.length();
+        if (need0count > 0) {
+            chunkId.insert(0, StringUtil.repeat('0', need0count));
         }
 
         return this.namePrefix
-            + chunkId.toUpperCase(Locale.ROOT)
+            + chunkId.toString().toUpperCase(Locale.ROOT)
             + type.toUpperCase(Locale.ROOT);
     }
 
diff --git a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/MAPIProperty.java b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/MAPIProperty.java
index 81c431b2b7b..3c3b5f533ea 100644
--- a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/MAPIProperty.java
+++ b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/MAPIProperty.java
@@ -17,6 +17,14 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 
 package org.apache.poi.hsmf.datatypes;
 
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Locale;
+import java.util.Map;
+
+import org.apache.poi.hsmf.datatypes.Types.MAPIType;
+
 import static org.apache.poi.hsmf.datatypes.Types.ASCII_STRING;
 import static org.apache.poi.hsmf.datatypes.Types.BINARY;
 import static org.apache.poi.hsmf.datatypes.Types.BOOLEAN;
@@ -27,14 +35,6 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import static org.apache.poi.hsmf.datatypes.Types.SHORT;
 import static org.apache.poi.hsmf.datatypes.Types.TIME;
 
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.Locale;
-import java.util.Map;
-
-import org.apache.poi.hsmf.datatypes.Types.MAPIType;
-
 /**
  * Holds the list of MAPI Attributes, and allows lookup by friendly name, ID and
  * MAPI Property Name.
@@ -1069,9 +1069,10 @@ private MAPIProperty(int id, MAPIType usualType, String name,
     }
 
     public String asFileName() {
-        String str = Integer.toHexString(id).toUpperCase(Locale.ROOT);
-        while (str.length() < 4) {
-            str = "0" + str;
+        StringBuilder str = new StringBuilder(Integer.toHexString(id).toUpperCase(Locale.ROOT));
+        int need0count = 4 - str.length();
+        if (need0count > 0) {
+            str.insert(0, StringUtil.repeat('0', need0count));
         }
         return str + usualType.asFileEnding();
     }
diff --git a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/PropertiesChunk.java b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/PropertiesChunk.java
index de28c70bbb2..5d5cde36ec1 100644
--- a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/PropertiesChunk.java
+++ b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/PropertiesChunk.java
@@ -17,8 +17,6 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 
 package org.apache.poi.hsmf.datatypes;
 
-import static org.apache.logging.log4j.util.Unbox.box;
-
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
@@ -48,6 +46,9 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import org.apache.poi.util.IOUtils;
 import org.apache.poi.util.LittleEndian;
 import org.apache.poi.util.LittleEndian.BufferUnderrunException;
+import org.apache.poi.util.StringUtil;
+
+import static org.apache.logging.log4j.util.Unbox.box;
 
 /**
  * <p>
@@ -419,9 +420,10 @@ private void writeVariableLengthValueHeader(OutputStream out, MAPIProperty prope
     }
 
     private String getFileName(MAPIProperty property, MAPIType actualType) {
-        String str = Integer.toHexString(property.id).toUpperCase(Locale.ROOT);
-        while (str.length() < 4) {
-            str = "0" + str;
+        StringBuilder str = new StringBuilder(Integer.toHexString(property.id).toUpperCase(Locale.ROOT));
+        int need0count = 4 - str.length();
+        if (need0count > 0) {
+            str.insert(0, StringUtil.repeat('0', need0count));
         }
         MAPIType type = getTypeMapping(actualType);
         return str + type.asFileEnding();
diff --git a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Types.java b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Types.java
index 4c92da4f0f2..d11f3489da4 100644
--- a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Types.java
+++ b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/datatypes/Types.java
@@ -21,6 +21,8 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import java.util.Locale;
 import java.util.Map;
 
+import org.apache.poi.util.StringUtil;
+
 /**
  * The types list and details are available from
  * http://msdn.microsoft.com/en-us/library/microsoft.exchange.data.contenttypes.tnef.tnefpropertytype%28v=EXCHG.140%29.aspx
@@ -148,11 +150,12 @@ public static MAPIType getById(int typeId) {
     }
 
     public static String asFileEnding(int type) {
-        String str = Integer.toHexString(type).toUpperCase(Locale.ROOT);
-        while (str.length() < 4) {
-            str = "0" + str;
+        StringBuilder str = new StringBuilder(Integer.toHexString(type).toUpperCase(Locale.ROOT));
+        int need0count = 4 - str.length();
+        if (need0count > 0) {
+            str.insert(0, StringUtil.repeat('0', need0count));
         }
-        return str;
+        return str.toString();
     }
 
     public static String asName(int typeId) {
diff --git a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/dev/TypesLister.java b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/dev/TypesLister.java
index 6cb05b30fb6..d29ffc2b944 100644
--- a/poi-scratchpad/src/main/java/org/apache/poi/hsmf/dev/TypesLister.java
+++ b/poi-scratchpad/src/main/java/org/apache/poi/hsmf/dev/TypesLister.java
@@ -22,6 +22,7 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import java.util.Comparator;
 
 import org.apache.poi.hsmf.datatypes.MAPIProperty;
+import org.apache.poi.util.StringUtil;
 
 /**
  * Lists the different MAPI types
@@ -49,8 +50,11 @@ public int compare(MAPIProperty a, MAPIProperty b) {
    }
    private void list(ArrayList<MAPIProperty> list, PrintStream out) {
       for(MAPIProperty attr : list) {
-         String id = Integer.toHexString(attr.id);
-         while(id.length() < 4) { id = "0"+id; }
+         StringBuilder id = new StringBuilder(Integer.toHexString(attr.id));
+         int need0count = 4 - id.length();
+         if (need0count > 0) {
+            id.insert(0, StringUtil.repeat('0', need0count));
+         }
          
          int typeId = attr.usualType.getId();
          String typeIdStr = Integer.toString(typeId);
diff --git a/poi-scratchpad/src/main/java/org/apache/poi/hwpf/converter/WordToHtmlUtils.java b/poi-scratchpad/src/main/java/org/apache/poi/hwpf/converter/WordToHtmlUtils.java
index 484d367788e..6bda01ee310 100644
--- a/poi-scratchpad/src/main/java/org/apache/poi/hwpf/converter/WordToHtmlUtils.java
+++ b/poi-scratchpad/src/main/java/org/apache/poi/hwpf/converter/WordToHtmlUtils.java
@@ -29,7 +29,7 @@ public class WordToHtmlUtils extends AbstractWordUtils
 {
     public static void addBold( final boolean bold, StringBuilder style )
     {
-        style.append( "font-weight:" + ( bold ? "bold" : "normal" ) + ";" );
+        style.append("font-weight:").append(bold ? "bold" : "normal").append(";");
     }
 
     public static void addBorder( BorderCode borderCode, String where,
@@ -71,13 +71,11 @@ public static void addCharactersProperties(
         }
         if ( characterRun.getIco24() != -1 )
         {
-            style.append( "color:" + getColor24( characterRun.getIco24() )
-                    + ";" );
+            style.append("color:").append(getColor24(characterRun.getIco24())).append(";");
         }
         if ( characterRun.isHighlighted() )
         {
-            style.append( "background-color:"
-                    + getColor( characterRun.getHighlightedColor() ) + ";" );
+            style.append("background-color:").append(getColor(characterRun.getHighlightedColor())).append(";");
         }
         if ( characterRun.isStrikeThrough() )
         {
@@ -85,8 +83,7 @@ public static void addCharactersProperties(
         }
         if ( characterRun.isShadowed() )
         {
-            style.append( "text-shadow:" + characterRun.getFontSize() / 24
-                    + "pt;" );
+            style.append("text-shadow:").append(characterRun.getFontSize() / 24).append("pt;");
         }
         if ( characterRun.isSmallCaps() )
         {
@@ -118,12 +115,12 @@ public static void addFontFamily( final String fontFamily,
         if ( isEmpty( fontFamily ) )
             return;
 
-        style.append( "font-family:" + fontFamily + ";" );
+        style.append("font-family:").append(fontFamily).append(";");
     }
 
     public static void addFontSize( final int fontSize, StringBuilder style )
     {
-        style.append( "font-size:" + fontSize + "pt;" );
+        style.append("font-size:").append(fontSize).append("pt;");
     }
 
     public static void addIndent( Paragraph paragraph, StringBuilder style )
@@ -143,7 +140,7 @@ private static void addIndent( StringBuilder style, final String cssName,
         if ( twipsValue == 0 )
             return;
 
-        style.append( cssName + ":" + ( twipsValue / TWIPS_PER_INCH ) + "in;" );
+        style.append(cssName).append(":").append(twipsValue / TWIPS_PER_INCH).append("in;");
     }
 
     public static void addJustification( Paragraph paragraph,
@@ -151,7 +148,7 @@ public static void addJustification( Paragraph paragraph,
     {
         String justification = getJustification( paragraph.getJustification() );
         if ( isNotEmpty( justification ) )
-            style.append( "text-align:" + justification + ";" );
+            style.append("text-align:").append(justification).append(";");
     }
 
     public static void addParagraphProperties( Paragraph paragraph,
@@ -170,8 +167,7 @@ public static void addParagraphProperties( Paragraph paragraph,
             style.append( "break-before:page;" );
         }
 
-        style.append( "hyphenate:"
-                + ( paragraph.isAutoHyphenated() ? "auto" : "none" ) + ";" );
+        style.append("hyphenate:").append(paragraph.isAutoHyphenated() ? "auto" : "none").append(";");
 
         if ( paragraph.keepOnPage() )
         {
@@ -188,12 +184,9 @@ public static void addTableCellProperties( TableRow tableRow,
             TableCell tableCell, boolean toppest, boolean bottomest,
             boolean leftest, boolean rightest, StringBuilder style )
     {
-        style.append( "width:" + ( tableCell.getWidth() / TWIPS_PER_INCH )
-                + "in;" );
-        style.append( "padding-start:"
-                + ( tableRow.getGapHalf() / TWIPS_PER_INCH ) + "in;" );
-        style.append( "padding-end:"
-                + ( tableRow.getGapHalf() / TWIPS_PER_INCH ) + "in;" );
+        style.append("width:").append(tableCell.getWidth() / TWIPS_PER_INCH).append("in;");
+        style.append("padding-start:").append(tableRow.getGapHalf() / TWIPS_PER_INCH).append("in;");
+        style.append("padding-end:").append(tableRow.getGapHalf() / TWIPS_PER_INCH).append("in;");
 
         BorderCode top = tableCell.getBrcTop() != null
                 && tableCell.getBrcTop().getBorderType() != 0 ? tableCell
@@ -224,8 +217,7 @@ public static void addTableRowProperties( TableRow tableRow,
     {
         if ( tableRow.getRowHeight() > 0 )
         {
-            style.append( "height:"
-                    + ( tableRow.getRowHeight() / TWIPS_PER_INCH ) + "in;" );
+            style.append("height:").append(tableRow.getRowHeight() / TWIPS_PER_INCH).append("in;");
         }
         if ( !tableRow.cantSplit() )
         {
diff --git a/poi-scratchpad/src/test/java/org/apache/poi/hwpf/TestFieldsTables.java b/poi-scratchpad/src/test/java/org/apache/poi/hwpf/TestFieldsTables.java
index 1e1b5b38418..6ee65376489 100644
--- a/poi-scratchpad/src/test/java/org/apache/poi/hwpf/TestFieldsTables.java
+++ b/poi-scratchpad/src/test/java/org/apache/poi/hwpf/TestFieldsTables.java
@@ -83,7 +83,7 @@ void testReadFields() {
     private String dumpPlexes(ArrayList<PlexOfField> fieldsPlexes) {
         StringBuilder dump = new StringBuilder();
         for (PlexOfField flds : fieldsPlexes) {
-            dump.append(flds + "\n");
+            dump.append(flds).append("\n");
         }
         return dump.toString();
     }
diff --git a/poi/src/main/java/org/apache/poi/hssf/usermodel/HSSFPalette.java b/poi/src/main/java/org/apache/poi/hssf/usermodel/HSSFPalette.java
index 3dcc5bccc0a..61ca511c2e7 100644
--- a/poi/src/main/java/org/apache/poi/hssf/usermodel/HSSFPalette.java
+++ b/poi/src/main/java/org/apache/poi/hssf/usermodel/HSSFPalette.java
@@ -22,6 +22,7 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import org.apache.poi.hssf.record.PaletteRecord;
 import org.apache.poi.hssf.util.HSSFColor;
 import org.apache.poi.hssf.util.HSSFColor.HSSFColorPredefined;
+import org.apache.poi.util.StringUtil;
 
 /**
  * Represents a workbook color palette.
@@ -218,22 +219,22 @@ public String getHexString() {
 
         private String getGnumericPart(byte color)
         {
-            String s;
+            StringBuilder s;
             if (color == 0)
             {
-                s = "0";
+                s = new StringBuilder("0");
             }
             else
             {
                 int c = color & 0xff; //as unsigned
                 c = (c << 8) | c; //pad to 16-bit
-                s = Integer.toHexString(c).toUpperCase(Locale.ROOT);
-                while (s.length() < 4)
-                {
-                    s = "0" + s;
+                s = new StringBuilder(Integer.toHexString(c).toUpperCase(Locale.ROOT));
+                int need0count = 4 - s.length();
+                if (need0count > 0) {
+                    s.insert(0, StringUtil.repeat('0', need0count));
                 }
             }
-            return s;
+            return s.toString();
         }
     }
 }
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/Bin2Dec.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/Bin2Dec.java
index 1ad45ea75e3..7096f915670 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/functions/Bin2Dec.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/Bin2Dec.java
@@ -22,6 +22,7 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import org.apache.poi.ss.formula.eval.OperandResolver;
 import org.apache.poi.ss.formula.eval.RefEval;
 import org.apache.poi.ss.formula.eval.ValueEval;
+import org.apache.poi.util.StringUtil;
 
 /**
  * Implementation for Excel Bin2Dec() function.
@@ -109,9 +110,12 @@ private int getDecimalValue(String unsigned) {
     private static String toggleBits(String s) {
         long i = Long.parseLong(s, 2);
         long i2 = i ^ ((1L << s.length()) - 1);
-        String s2 = Long.toBinaryString(i2);
-        while (s2.length() < s.length()) s2 = '0' + s2;
-        return s2;
+        StringBuilder s2 = new StringBuilder(Long.toBinaryString(i2));
+        int need0count = s.length() - s2.length();
+        if (need0count > 0) {
+            s2.insert(0, StringUtil.repeat('0', need0count));
+        }
+        return s2.toString();
     }
 
     @Override
diff --git a/poi/src/main/java/org/apache/poi/util/StringUtil.java b/poi/src/main/java/org/apache/poi/util/StringUtil.java
index e0ac29b4cdf..0b292ece4ab 100644
--- a/poi/src/main/java/org/apache/poi/util/StringUtil.java
+++ b/poi/src/main/java/org/apache/poi/util/StringUtil.java
@@ -21,8 +21,11 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
 import java.util.Locale;
 
+import org.apache.logging.log4j.util.Strings;
+
 /**
  * Collection of string handling utilities
  */
@@ -759,4 +762,34 @@ public static boolean isNotBlank(final CharSequence cs) {
         return !isBlank(cs);
     }
 
+    /**
+     * <p>Returns padding using the specified delimiter repeated
+     * to a given length.</p>
+     *
+     * <pre>
+     * StringUtil.repeat('e', 0)  = ""
+     * StringUtil.repeat('e', 3)  = "eee"
+     * StringUtil.repeat('e', -2) = ""
+     * </pre>
+     *
+     * <p>Note: this method does not support padding with
+     * <a href="http://www.unicode.org/glossary/#supplementary_character">Unicode Supplementary Characters</a>
+     * as they require a pair of {@code char}s to be represented.
+     * </p>
+     *
+     * copied from commons-lang3
+     *
+     * @param ch  character to repeat
+     * @param repeat  number of times to repeat char, negative treated as zero
+     * @return String with repeated character
+     */
+    public static String repeat(final char ch, final int repeat) {
+        if (repeat <= 0) {
+            return Strings.EMPTY;
+        }
+        final char[] buf = new char[repeat];
+        Arrays.fill(buf, ch);
+        return new String(buf);
+    }
+
 }
diff --git a/poi/src/test/java/org/apache/poi/hssf/eventusermodel/TestMissingRecordAwareHSSFListener.java b/poi/src/test/java/org/apache/poi/hssf/eventusermodel/TestMissingRecordAwareHSSFListener.java
index 1dfd056ab6b..c2f8d8486b1 100644
--- a/poi/src/test/java/org/apache/poi/hssf/eventusermodel/TestMissingRecordAwareHSSFListener.java
+++ b/poi/src/test/java/org/apache/poi/hssf/eventusermodel/TestMissingRecordAwareHSSFListener.java
@@ -212,7 +212,7 @@ private String digest(int start, int len) {
                 dig = "ur";
             }
             if (lastRow != row && row > -1) {
-                sb.append((lastRow > -1 ? "," : "") + row + ":");
+                sb.append(lastRow > -1 ? "," : "").append(row).append(":");
                 lastRow = row;
             }
             sb.append(dig);
diff --git a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestIrr.java b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestIrr.java
index b4830e09d3f..8071b8d8cdf 100644
--- a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestIrr.java
+++ b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestIrr.java
@@ -106,7 +106,7 @@ void testIrrFromSpreadsheet(){
                 assertFormulaResult(cv, cellA);
             } catch (Throwable e){
                 if(failures.length() > 0) failures.append('\n');
-                failures.append("Row[" + (cellA.getRowIndex() + 1)+ "]: " + cellA.getCellFormula() + " ");
+                failures.append("Row[").append(cellA.getRowIndex() + 1).append("]: ").append(cellA.getCellFormula()).append(" ");
                 failures.append(e.getMessage());
             }
 
@@ -116,7 +116,7 @@ void testIrrFromSpreadsheet(){
                 assertEquals(0, cv.getNumberValue(), 0.0001);  // should agree within 0.01%
             } catch (Throwable e){
                 if(failures.length() > 0) failures.append('\n');
-                failures.append("Row[" + (cellC.getRowIndex() + 1)+ "]: " + cellC.getCellFormula() + " ");
+                failures.append("Row[").append(cellC.getRowIndex() + 1).append("]: ").append(cellC.getCellFormula()).append(" ");
                 failures.append(e.getMessage());
             }
         }