Java – fast double string conversion with given precision

I need to convert double to string with the given precision String. Format ("%. 3F", value) (or decimalformat) executes the job, but the benchmark shows that it is not very fast double ToString conversion (about 1-3 seconds to convert 1 million numbers on my machine))

Is there a better way?

Updating: benchmark results

Random numbers range from 0 to 1000000, resulting in operations per millisecond (Java 1.7.0_45)

Benchmark                                    Mean   Mean error    Units

String_format                             747.394       13.197   ops/ms
BigDecimal_toPlainString                 1349.552       31.144   ops/ms
DecimalFormat_format                     1890.917       28.886   ops/ms
Double_toString                          3341.941       85.453   ops/ms
DoubleFormatUtil_formatDouble            7760.968       87.630   ops/ms
SO_User_format                          14269.388      168.206   ops/ms

Solution

Disclaimer: I only recommend that you use this speed is an absolute requirement

On my machine, the following can complete 1 million conversions in 130ms:

private static final int POW10[] = {1,10,100,1000,10000,100000,1000000};

 public static String format(double val,int precision) {
     StringBuilder sb = new StringBuilder();
     if (val < 0) {
         sb.append('-');
         val = -val;
     }
     int exp = POW10[precision];
     long lval = (long)(val * exp + 0.5);
     sb.append(lval / exp).append('.');
     long fval = lval % exp;
     for (int p = precision - 1; p > 0 && fval < POW10[p]; p--) {
         sb.append('0');
     }
     sb.append(fval);
     return sb.toString();
 }

The code provided has several disadvantages: it can only handle limited doubles and does not handle Nan The former can be solved by expanding pow10 array (but only partially) The latter can be handled explicitly in the code