我要你扮演一个软件工程师。现在我需要你仔细思考，以下代码存在一些问题，headClazz里面获取到的是空值，我想要headClazz能动态获取到entity包中的user、admin表，我需要你指出代码错误，以及改正方法。代码如下：public class CommonReadListener<T> extends AnalysisEventListener<T> implements ReadListener<T> {private Class<T> headClazz;public CommonReadListener(Class<T> headClazz) { this.headClazz = headClazz; }@Override public void invokeHead(Map<Integer, ReadCellData<?>> headMap, AnalysisContext context) { ExcelPropertyCheck clazzHeadAnno = this.headClazz.getAnnotation(ExcelPropertyCheck.class); Field[] declaredFields = headClazz.getDeclaredFields(); if (clazzHeadAnno != null && clazzHeadAnno.required()) { for (Field declaredField : declaredFields) { nullAbleFieldMap.put(declaredField.getName(), true); } } for (Field declaredField : declaredFields) { ExcelPropertyCheck annotation = declaredField.getAnnotation(ExcelPropertyCheck.class); if (annotation != null) { if (annotation.checkFormat()) { checkFormatFieldMap.put(declaredField.getName(), annotation.type() + ""); } if (annotation.required()) { nullAbleFieldMap.put(declaredField.getName(), true); } else { nullAbleFieldMap.remove(declaredField.getName()); } if (annotation.required() && annotation.length() != -1) { checkLengthFieldMap.put(declaredField.getName(), annotation.length()); } } } }

这段代码中，headClazz是一个类类型参数，它通过构造方法传入，但是在代码中没有看到headClazz的值在哪里被设置。所以，获取到的headClazz为null。

要让headClazz能够动态获取到entity包中的user、admin表，可以使用Java反射机制来实现。可以添加一个参数tableName，用来指定表名，然后通过反射获取指定表名对应的类，最后将获取的类作为headClazz的值。

修改后的代码如下：

public class CommonReadListener<T> extends AnalysisEventListener<T> implements ReadListener<T> {

    private Class<T> headClazz;

    public CommonReadListener(Class<T> headClazz) { 
        this.headClazz = headClazz; 
    }

    public CommonReadListener(String tableName) {
        try {
            String className = "entity." + tableName;
            Class<T> clazz = (Class<T>) Class.forName(className);
            this.headClazz = clazz;
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void invokeHead(Map<Integer, ReadCellData<?>> headMap, AnalysisContext context) {
        ExcelPropertyCheck clazzHeadAnno = this.headClazz.getAnnotation(ExcelPropertyCheck.class);
        Field[] declaredFields = headClazz.getDeclaredFields();
        if (clazzHeadAnno != null && clazzHeadAnno.required()) {
            for (Field declaredField : declaredFields) {
                nullAbleFieldMap.put(declaredField.getName(), true);
            }
        }
        for (Field declaredField : declaredFields) {
            ExcelPropertyCheck annotation = declaredField.getAnnotation(ExcelPropertyCheck.class);
            if (annotation != null) {
                if (annotation.checkFormat()) {
                    checkFormatFieldMap.put(declaredField.getName(), annotation.type() + "");
                }
                if (annotation.required()) {
                    nullAbleFieldMap.put(declaredField.getName(), true);
                } else {
                    nullAbleFieldMap.remove(declaredField.getName());
                }
                if (annotation.required() && annotation.length() != -1) {
                    checkLengthFieldMap.put(declaredField.getName(), annotation.length());
                }
            }
        }
    }
}

使用方法：

CommonReadListener<User> userListener = new CommonReadListener<>("user");
CommonReadListener<Admin> adminListener = new CommonReadListener<>("admin");