CacheBuilder 使用番石榴缓存查询结果

Question

为了减少使用query 从数据库读取数据的数据库命中，我计划将结果保存在缓存中。为此，我使用了番石榴缓存。

studentController.java

public Map<String, Object> getSomeMethodName(Number departmentId, String departmentType){
    ArrayList<Student> studentList = studentManager.getStudentListByDepartmentType(departmentId, departmentType);
    ----------
    ----------
    }

StudentHibernateDao.java（条件查询）

@Override
    public ArrayList<Student> getStudentListByDepartmentType(Number departmentId, String departmentType) {
        Criteria criteria =sessionFactory.getCurrentSession().createCriteria(Student.class);
        criteria.add(Restrictions.eq("departmentId", departmentId));
        criteria.add(Restrictions.eq("departmentType", departmentType));
        ArrayList<Student> studentList = (ArrayList)criteria.list();
        return studentList;
    }

为了缓存条件查询结果，我开始构建 CacheBuilder，如下所示。

private static LoadingCache<Number departmentId, String departmentType, ArrayList<Student>> studentListCache = CacheBuilder
            .newBuilder().expireAfterAccess(1, TimeUnit.MINUTES)
            .maximumSize(1000)
            .build(new CacheLoader<Number departmentId, String departmentType, ArrayList<Student>>() {
                public ArrayList<Student> load(String key) throws Exception {
                    return getStudentListByDepartmentType(departmentId, departmentType);
                }
            });

这里我不知道将CacheBuilder函数放在哪里以及如何将多个关键参数（即departmentId和departmentType）传递给CacheLoader并调用它。

这是使用guava 进行缓存的正确方法吗？我错过了什么吗？

Answer 1

Guava 的缓存只接受两个类型参数，一个键类型和一个值类型。如果您希望您的键是复合键，那么您需要构建一个新的 compound 类型来封装它。实际上它需要看起来像这样（我为我的语法道歉，我不经常使用 Java）：

// Compound Key type
class CompoundDepartmentId {
  public CompoundDepartmentId(Long departmentId, String departmentType) {
    this.departmentId = departmentId;
    this.departmentType = departmentType;
  }
}

private static LoadingCache<CompoundDepartmentId, ArrayList<Student>> studentListCache = 
  CacheBuilder
    .newBuilder().expireAfterAccess(1, TimeUnit.MINUTES)
    .maximumSize(1000)
    .build(new CacheLoader<CompoundDepartmentId, ArrayList<Student>>() {
      public ArrayList<Student> load(CompoundDepartmentId key) throws Exception {
        return getStudentListByDepartmentType(key.departmentId, key.departmentType);
      }
    });