java获取泛型类型T的declaredFields

Question

我有一个泛型类，定义如下：

 public class ExcelParser<T> {
    private Workbook workbook;

    public ExcelParser(InputStream is){
      workbook = new HSSFWorkbook(new POIFSFileSystem(new ByteArrayInputStream(bytes)));
    }

    public List<T> retrieveRecordList() {
        Field[] fields = T.class.getDeclaredFields();// here will give a error
    }
 }

我试图编写一个泛型类，将excel记录云解析为javabean list，但我无法从泛型类型t获取declaredFields，有什么方法可以做到这一点吗

Answer 1

您应该将Class<T>存储在ExcelParser类中，以便在运行时获取关于T的元信息：

public class ExcelParser<T> {
    private Workbook workbook;
    private Class<T> clazz;

    public ExcelParser(InputStream is, Class<T> clazz) {
      workbook = new HSSFWorkbook(new POIFSFileSystem(new ByteArrayInputStream(bytes)));
      this.clazz = clazz;
    }

    public List<T> retrieveRecordList() throws Exception {
        Field[] fields = clazz.getDeclaredFields();
    }
}

Answer 2

向构造函数添加字段classT和伪参数

public class ExcelParser<T> {
    private Workbook workbook;

    private final Class<?> classT;

    @SafeVarargs
    public ExcelParser(InputStream is, T... dummyArguments){
      workbook = new HSSFWorkbook(new POIFSFileSystem(new ByteArrayInputStream(bytes)));
        classT = dummyArguments.getClass().getComponentType();
        System.out.println(classT);
    }

并在没有dummyArguments的情况下调用构造函数

    ExcelParser<Baz> parser = new ExcelParser<>(is /* no dummyArguments */);

classT被分配给Baz.class