diff --git a/test/micro/org/openjdk/bench/java/net/URLEncodeDecode.java b/test/micro/org/openjdk/bench/java/net/URLEncodeDecode.java
index 1bd98f9ed52..a599a68f924 100644
--- a/test/micro/org/openjdk/bench/java/net/URLEncodeDecode.java
+++ b/test/micro/org/openjdk/bench/java/net/URLEncodeDecode.java
@@ -37,6 +37,7 @@ import org.openjdk.jmh.infra.Blackhole;
 
 import java.io.UnsupportedEncodingException;
 import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
 import java.util.Random;
 import java.util.concurrent.TimeUnit;
 
@@ -51,78 +52,140 @@ import java.util.concurrent.TimeUnit;
 @Fork(value = 3)
 public class URLEncodeDecode {
 
-    @Param("1024")
-    public int count;
+    private static final int COUNT = 1024;
 
     @Param("1024")
     public int maxLength;
 
-    @Param("3")
-    public long mySeed;
+    /**
+     * Percentage of strings that will remain unchanged by an encoding/decoding (0-100)
+     */
+    @Param({"0", "75", "100"})
+    public int unchanged;
+
+    /**
+     * Percentage of chars in changed strings that cause encoding/decoding to happen (0-100)
+     */
+    @Param({"6"})
+    public int encodeChars;
 
     public String[] testStringsEncode;
     public String[] testStringsDecode;
     public String[] toStrings;
 
-    @Setup
+    @Setup()
     public void setupStrings() {
-        char[] tokens = new char[((int) 'Z' - (int) 'A' + 1) + ((int) 'z' - (int) 'a' + 1) + ((int) '9' - (int) '1' + 1) + 5];
+        char[] encodeTokens = new char[] { '[', '(', ' ', '\u00E4', '\u00E5', '\u00F6', ')', '='};
+        char[] tokens = new char[('Z' - 'A' + 1) + ('z' - 'a' + 1) + ('9' - '0' + 1) + 4];
         int n = 0;
-        tokens[n++] = '0';
-        for (int i = (int) '1'; i <= (int) '9'; i++) {
-            tokens[n++] = (char) i;
+        for (char c = '0'; c <= '9'; c++) {
+            tokens[n++] = c;
         }
-        for (int i = (int) 'A'; i <= (int) 'Z'; i++) {
-            tokens[n++] = (char) i;
+        for (char c = 'A'; c <= 'Z'; c++) {
+            tokens[n++] = c;
         }
-        for (int i = (int) 'a'; i <= (int) '<'; i++) {
-            tokens[n++] = (char) i;
+        for (char c = 'a'; c <= 'z'; c++) {
+            tokens[n++] = c;
         }
         tokens[n++] = '-';
         tokens[n++] = '_';
         tokens[n++] = '.';
-        tokens[n++] = '*';
+        tokens[n] = '*';
 
-        Random r = new Random(mySeed);
-        testStringsEncode = new String[count];
-        testStringsDecode = new String[count];
-        toStrings = new String[count];
-        for (int i = 0; i < count; i++) {
+        Random r = new Random(3);
+        testStringsEncode = new String[COUNT];
+        testStringsDecode = new String[COUNT];
+        toStrings = new String[COUNT];
+        for (int i = 0; i < COUNT; i++) {
             int l = r.nextInt(maxLength);
+            boolean needEncoding = r.nextInt(100) >= unchanged;
             StringBuilder sb = new StringBuilder();
+            boolean hasEncoded = false;
             for (int j = 0; j < l; j++) {
-                int c = r.nextInt(tokens.length);
-                sb.append(tokens[c]);
+                if (needEncoding && r.nextInt(100) < encodeChars) {
+                    addToken(encodeTokens, r, sb);
+                    hasEncoded = true;
+                } else {
+                    addToken(tokens, r, sb);
+                }
+            }
+            if (needEncoding && !hasEncoded) {
+                addToken(encodeTokens, r, sb);
             }
             testStringsEncode[i] = sb.toString();
         }
-
-        for (int i = 0; i < count; i++) {
-            int l = r.nextInt(maxLength);
-            StringBuilder sb = new StringBuilder();
-            for (int j = 0; j < l; j++) {
-                int c = r.nextInt(tokens.length + 5);
-                if (c >= tokens.length) {
-                    sb.append("%").append(tokens[r.nextInt(16)]).append(tokens[r.nextInt(16)]);
-                } else {
-                    sb.append(tokens[c]);
+        int countUnchanged = 0;
+        for (String s : testStringsEncode) {
+            if (s.equals(java.net.URLEncoder.encode(s, StandardCharsets.UTF_8))) {
+                countUnchanged++;
+            } else {
+                if (unchanged == 100) {
+                    System.out.println("Unexpectedly needs encoding action: ");
+                    System.out.println("\t" + s);
+                    System.out.println("\t" + java.net.URLEncoder.encode(s, StandardCharsets.UTF_8));
                 }
             }
+        }
+        System.out.println();
+        System.out.println("Generated " + testStringsEncode.length + " encodable strings, " + countUnchanged + " of which does not need encoding action");
+
+        for (int i = 0; i < COUNT; i++) {
+            int l = r.nextInt(maxLength);
+            boolean needDecoding = r.nextInt(100) >= unchanged;
+            StringBuilder sb = new StringBuilder();
+            boolean hasDecoded = false;
+            for (int j = 0; j < l; j++) {
+                if (needDecoding && r.nextInt(100) < encodeChars) {
+                    addDecodableChar(tokens, r, sb);
+                    hasDecoded = true;
+                } else {
+                    addToken(tokens, r, sb);
+                }
+            }
+            if (needDecoding && !hasDecoded) {
+                addDecodableChar(tokens, r, sb);
+            }
             testStringsDecode[i] = sb.toString();
         }
+        countUnchanged = 0;
+        for (String s : testStringsDecode) {
+            if (s.equals(java.net.URLDecoder.decode(s, StandardCharsets.UTF_8))) {
+                countUnchanged++;
+            } else {
+                if (unchanged == 100) {
+                    System.out.println("Unexpectedly needs encoding action: ");
+                    System.out.println("\t" + s);
+                    System.out.println("\t" + java.net.URLDecoder.decode(s, StandardCharsets.UTF_8));
+                }
+            }
+        }
+        System.out.println("Generated " + testStringsDecode.length + " decodable strings, " + countUnchanged + " of which does not need decoding action");
+    }
+
+    private static void addToken(char[] tokens, Random r, StringBuilder sb) {
+        int c = r.nextInt(tokens.length);
+        sb.append(tokens[c]);
+    }
+
+    private static void addDecodableChar(char[] tokens, Random r, StringBuilder sb) {
+        if (r.nextInt(100) < 15) {
+            sb.append('+'); // exercise '+' -> ' ' decoding paths.
+        } else {
+            sb.append("%").append(tokens[r.nextInt(16)]).append(tokens[r.nextInt(16)]);
+        }
     }
 
     @Benchmark
     public void testEncodeUTF8(Blackhole bh) throws UnsupportedEncodingException {
         for (String s : testStringsEncode) {
-            bh.consume(java.net.URLEncoder.encode(s, "UTF-8"));
+            bh.consume(java.net.URLEncoder.encode(s, StandardCharsets.UTF_8));
         }
     }
 
     @Benchmark
     public void testDecodeUTF8(Blackhole bh) throws UnsupportedEncodingException {
         for (String s : testStringsDecode) {
-            bh.consume(URLDecoder.decode(s, "UTF-8"));
+            bh.consume(URLDecoder.decode(s, StandardCharsets.UTF_8));
         }
     }