有如下方法：

String testString = "a,b,c,d"

1)using apache commons

int apache = StringUtils.countMatches(testString, ".");
System.out.println("apache = " + apache);

2) Using Spring Framework's

int occurance = StringUtils.countOccurrencesOf("a.b.c.d", ".");

3) Using replace

int replace = testString.length
 
() - testString.replace(".", "").length();
System.out.println("replace = " + replace);

4) Using replaceAll (case 1)

int replaceAll = testString.replaceAll("[^.]", "").length();

5) Using replaceAll (case 2)

int replaceAllCase2 = testString.length() - testString.replaceAll("\\.", "").length();
System.out
 
.println("replaceAll (second case) = " + replaceAllCase2);

6) Using split

int split = testString.split("\\.",-1).length-1;
System.out.println("split = " + split);

7) Using Java8 (case 1)

long java8 = testString.chars().filter(ch -> ch =='.').count();
System.out.println("java8 = " + java8);

8) Using Java8 (case 2), may be better for unicode than case 1
 

long java8Case2 = testString.codePoints().filter(ch -> ch =='.').count();
System.out.println("java8 (second case) = " + java8Case2);

9) Using StringTokenizer

int stringTokenizer = new StringTokenizer(" " +testString + " ", ".").countTokens()-1;
System.out.println("stringTokenizer = " + stringTokenizer);