如何获取作为通用接收的类的所有字段信息？

Question

如何获取作为通用接收的类的所有字段信息？

我给Account.class作为GenericClass的构造函数，并执行t1.getClass().getDeclaredFields();命令来获取该类的字段信息。

但结果，declaredFields的大小为0。

调试结果显示以下结果。

result = {Field[21]@10835}
 0 = {Field@10837} "private static final int java.lang.Class.ANNOTATION"
 1 = {Field@10838} "private static final int java.lang.Class.ENUM"
 2 = {Field@10839} "private static final int java.lang.Class.SYNTHETIC"
 3 = {Field@10840} "private transient volatile java.lang.reflect.Constructor java.lang.Class.cachedConstructor"
 4 = {Field@10841} "private transient java.lang.String java.lang.Class.name"
 5 = {Field@10842} "private transient java.lang.Module java.lang.Class.module"
 6 = {Field@10843} "private transient java.lang.String java.lang.Class.packageName"
 7 = {Field@10844} "private final java.lang.Class java.lang.Class.componentType"
 8 = {Field@10845} "private static java.security.ProtectionDomain java.lang.Class.allPermDomain"
 9 = {Field@10846} "private transient volatile java.lang.ref.SoftReference java.lang.Class.reflectionData"
 10 = {Field@10847} "private transient volatile int java.lang.Class.classRedefinedCount"
 11 = {Field@10848} "private transient volatile sun.reflect.generics.repository.ClassRepository java.lang.Class.genericInfo"
 12 = {Field@10849} "private static final java.lang.Class[] java.lang.Class.EMPTY_CLASS_ARRAY"
 13 = {Field@10850} "private static final long java.lang.Class.serialVersionUID"
 14 = {Field@10851} "private static final java.io.ObjectStreamField[] java.lang.Class.serialPersistentFields"
 15 = {Field@10852} "private static jdk.internal.reflect.ReflectionFactory java.lang.Class.reflectionFactory"
 16 = {Field@10853} "private transient volatile java.lang.Object[] java.lang.Class.enumConstants"
 17 = {Field@10854} "private transient volatile java.util.Map java.lang.Class.enumConstantDirectory"
 18 = {Field@10855} "private transient volatile java.lang.Class$AnnotationData java.lang.Class.annotationData"
 19 = {Field@10856} "private transient volatile sun.reflect.annotation.AnnotationType java.lang.Class.annotationType"
 20 = {Field@10857} "transient java.lang.ClassValue$ClassValueMap java.lang.Class.classValueMap"

账户信息如下。

@Entity
@Getter
@Setter
public class Account{
    @Id
    @GeneratedValue
    @Column(name = "account_id", nullable = false)
    private Long id;

    // User ID
    @Column(unique = true, nullable = false)
    private String userid;

    // username
    private String username;

    // user password
    private String password;

    // User Permissions
    @Enumerated(EnumType.STRING)
    private AccountRole role;

测试代码如下。

@SpringBootTest
class PlxEntityToExcelTest {
    
    @Autowired
    AccountRepository accountRepository;

    @Autowired
    AccountService accountService;

    @Test
    void basic() {
        System.out.println("accountRepository = " + accountRepository);
        Iterable<Account> all = accountRepository.findAll();
        for (Account account: all) {
            System.out.println("account = " + account);
        }
    }

    @Test
    void anyClass() {
        Account account = new Account();
        account.setUserid("test");
        account.setUsername("username");
        account.setPassword("qwer");
        account.setRole(AccountRole.USER);
        accountService.createAccount(account);

        Iterable<Account> all = accountRepository.findAll();

        GenericClass<Account> cn = new GenericClass<Account>(Account.class);
        cn.entityToExcel((List<Account>) all);




    }

    public class GenericClass<T>{
        private T t1;



        public GenericClass(Class<T> specificClass) {
            this.t1 = (T) specificClass;
        }

        private void createHeader(){

            Field[] declaredFields = t1.getClass().getDeclaredFields();


        }
        public void entityToExcel(List<T> list) {
            System.out.println("list = " + list);
            createHeader();
        }
    }
}

Answer 1

如果我正确理解你想要做什么，你正在尝试获取类 Account 的字段。在这种情况下，您不需要在 GenericClass 的构造函数中将 clazz 实例强制转换为 Account 实例，因此您只需执行 t1.getDeclaredFields();

以下是经过正确更改的代码：泛型类

public class GenericClass<T>{
    private Class<T> t1;



    public GenericClass(Class<T> specificClass) {
        this.t1 = specificClass;
    }

    private void createHeader(){
        Field[] declaredFields = t1.getDeclaredFields();


    }
    public void entityToExcel(List<T> list) {
        System.out.println("list = " + list);
        createHeader();
    }
}