Test case to show String.substring(int) performance issue for Java 7u06 and later.

Test.java

/**
 * Test class to show a huge performance dump in Java 7u06/u07 for the {@link String#substring(int)} compared to
 * {@link String#substring(int, int)}. On versions before 7u06 I get numbers like 23ms for the first method call and
 * 12ms for the second. On update 6 and 7 I get 10483ms for the first call, 16ms for the second.
 * <p>
 * The issue seems to be related to a fix in related to {@code Arrays.copyOnWrite} (this is the hotspot the profiler
 * unveiled) introduced with update 6 (see links below).
 * <p>
 * Feel free to add your numbers in the comments below.
 * 
 * @see http://mail.openjdk.java.net/pipermail/core-libs-dev/2012-May/010257.html
 * @see http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7174363
 * @see http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=2226462
 * @author Oliver Gierke
 */
public class Test {

	public static void main(String... args) throws Exception {

		StringBuilder builder = new StringBuilder();
		for (int i = 0; i < 1000 * 100; i++) {
			builder.append(" ");
		}

		String source = builder.toString();

		long before = System.currentTimeMillis();
		criticalCode(source);
		long after = System.currentTimeMillis();

		System.out.println(String.format("%sms", after - before));

		before = System.currentTimeMillis();
		criticalCode2(source);
		after = System.currentTimeMillis();

		System.out.println(String.format("%sms", after - before));
	}

	private static void criticalCode(String value) {

		for (int i = 0; i < value.length(); i++) {
			value.substring(i);
		}
	}

	private static void criticalCode2(String value) {

		for (int i = 0; i < value.length(); i++) {
			value.substring(i, i + 1);
		}
	}
}

@pidster I know, I initialy reported it. https://jira.springsource.org/browse/SPR-9781 Only wanted to let Oliver know, that the latter is not in any case a replacement for the former.

Just ran into this after upgrading an ubuntu server to 7u7.

2802ms was 5ms
7ms was 3ms