Reduce memory allocation in Parser.setSQL()

h2/src/main/org/h2/command/Parser.java

@@ -2687,9 +2687,14 @@ public class Parser {
     }
 
     private void setSQL(Prepared command, String start, int startIndex) {
-        String sql = StringUtils.trimSubstring(originalSQL, startIndex, lastParseIndex);
+        int endIndex = lastParseIndex;
+        String sql;
         if (start != null) {
-            sql = start + " " + sql;
+            StringBuilder builder = new StringBuilder(start.length() + endIndex - startIndex + 1)
+                    .append(start).append(' ');
+            sql = StringUtils.trimSubstring(builder, originalSQL, startIndex, endIndex).toString();
+        } else {
+            sql = StringUtils.trimSubstring(originalSQL, startIndex, endIndex);
         }
         command.setSQL(sql);
     }

h2/src/main/org/h2/jdbc/JdbcDatabaseMetaData.java

@@ -1624,11 +1624,12 @@ public class JdbcDatabaseMetaData extends TraceObject implements
                     int spaceIndex = f.indexOf(' ');
                     if (spaceIndex >= 0) {
                         // remove 'Function' from 'INSERT Function'
-                        f = StringUtils.trimSubstring(f, 0, spaceIndex);
-                    }
+                        StringUtils.trimSubstring(buff.builder(), f, 0, spaceIndex);
+                    } else {
                         buff.append(f);
                     }
                 }
+            }
             rs.close();
             prep.close();
             return buff.toString();

h2/src/main/org/h2/util/StringUtils.java

@@ -872,7 +872,7 @@ public class StringUtils {
     }
 
     /**
-     * Trim a character from a substring. Equivalent of
+     * Trim a whitespace from a substring. Equivalent of
      * {@code substring(beginIndex).trim()}.
      *
      * @param s the string
@@ -884,7 +884,7 @@ public class StringUtils {
     }
 
     /**
-     * Trim a character from a substring. Equivalent of
+     * Trim a whitespace from a substring. Equivalent of
      * {@code substring(beginIndex, endIndex).trim()}.
      *
      * @param s the string
@@ -902,6 +902,27 @@ public class StringUtils {
         return s.substring(beginIndex, endIndex);
     }
 
+    /**
+     * Trim a whitespace from a substring and append it to a specified string
+     * builder. Equivalent of
+     * {@code builder.append(substring(beginIndex, endIndex).trim())}.
+     *
+     * @param builder string builder to append to
+     * @param s the string
+     * @param beginIndex start index of substring (inclusive)
+     * @param endIndex end index of substring (exclusive)
+     * @return the specified builder
+     */
+    public static StringBuilder trimSubstring(StringBuilder builder, String s, int beginIndex, int endIndex) {
+        while (beginIndex < endIndex && s.charAt(beginIndex) <= ' ') {
+            beginIndex++;
+        }
+        while (beginIndex < endIndex && s.charAt(endIndex - 1) <= ' ') {
+            endIndex--;
+        }
+        return builder.append(s, beginIndex, endIndex);
+    }
+
     /**
      * Get the string from the cache if possible. If the string has not been
      * found, it is added to the cache. If there is such a string in the cache,

h2/src/test/org/h2/test/unit/TestStringUtils.java

@@ -281,14 +281,22 @@ public class TestStringUtils extends TestBase {
     }
 
     private void testTrimSubstring() {
-        assertEquals("", StringUtils.trimSubstring("", 0, 0));
-        assertEquals("", StringUtils.trimSubstring("    ", 0, 0));
-        assertEquals("", StringUtils.trimSubstring("    ", 4, 4));
-        assertEquals("select", StringUtils.trimSubstring(" select  from", 1, 7));
-        assertEquals("a b", StringUtils.trimSubstring(" a b ", 1, 4));
+        testTrimSubstringImpl("", "", 0, 0);
+        testTrimSubstringImpl("", "    ", 0, 0);
+        testTrimSubstringImpl("", "    ", 4, 4);
+        testTrimSubstringImpl("select", " select  from", 1, 7);
+        testTrimSubstringImpl("a b", " a b ", 1, 4);
+        testTrimSubstringImpl("a b", " a b ", 1, 5);
+        testTrimSubstringImpl("b", " a b ", 2, 5);
         new AssertThrows(StringIndexOutOfBoundsException.class) { @Override
             public void test() { StringUtils.trimSubstring(" with (", 1, 8); }
         };
     }
 
+    private void testTrimSubstringImpl(String expected, String string, int startIndex, int endIndex) {
+        assertEquals(expected, StringUtils.trimSubstring(string, startIndex, endIndex));
+        assertEquals(expected, StringUtils
+                .trimSubstring(new StringBuilder(endIndex - startIndex), string, startIndex, endIndex).toString());
+    }
+
 }