RFR: 8058230: Improve java.sql toString formatting

[Claes Redestad]

Hi,

requesting reviews for this patch which optimizes 
java.sql.Date/Time/Timestamp::toString
by avoiding some unnecessary object allocations. java.sql.Date had 
similar optimizations
applied which this patch improves upon.

bug: https://bugs.openjdk.java.net/browse/JDK-8058230
webrev: http://cr.openjdk.java.net/~redestad/8058230/webrev.00/

Testing: jtreg jdk/test/java/sql with and without 8057826 tests

Before/after performance running a minimal JMH micro[1]:

Benchmark                         Mode  Samples      Score Score error   
Units
t.DateBench.dateToString         thrpt       20 30225.628      623.887  
ops/ms
t.DateBench.dateToString         thrpt       20 38350.173     1349.432  
ops/ms  # 1.3x

t.DateBench.timeToString         thrpt       20 11793.338      232.121  
ops/ms
t.DateBench.timeToString         thrpt       20 47048.344     1969.939  
ops/ms  # 4.0x

t.DateBench.timestampToString    thrpt       20 2529.601       45.990  
ops/ms
t.DateBench.timestampToString    thrpt       20 14143.612      407.351  
ops/ms  # 5.6x

/Claes

[1]

package test;

import org.openjdk.jmh.annotations.*;

@State(Scope.Thread)
public class DateBench {

     public java.sql.Time time = java.sql.Time.valueOf("15:15:25");

     @Benchmark
     public String timeToString() {
         return time.toString();
     }

     public java.sql.Date date = java.sql.Date.valueOf("2013-01-01");

     @Benchmark
     public String dateToString() {
         return date.toString();
     }

     public Timestamp timestamp = Timestamp.valueOf("1999-12-13 
15:15:25.645634");

     @Benchmark
     public String timestampToString() {
         return timestamp.toString();
     }

}