ObjectMapper mapper=new ObjectMapper();
//3.调用mapper的writeValueAsString()方法把一个对象或集合转为json字符串
Customer customer=new Customer("aaa", "333");
String jsonStr=mapper.writeValueAsString(customer);
System.out.println(jsonStr);
//4.注意：jackson使用getter方法来定位json对象的属性
//5.可以通过添加注解JsonIgnore忽略某一个getter定义的属性
List<Customer> customers=Arrays.asList(customer,new Customer("bb", "213"));
jsonStr=mapper.writeValueAsString(customers);
System.out.println(jsonStr);