Cách nhanh nhất là sử dụng thư viện JsonPath (com.jayway.jsonpath.JsonPath)
Pom.xml
<dependency>
<groupId>com.jayway.jsonpath</groupId>
<artifactId>json-path</artifactId>
<version>2.6.0</version>
</dependency>String res = "[{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{}]";
List<Object> list = JsonPath.read(res, "$[*]");
System.out.println(list.size());
//25