java注解

import DAO.Filter;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Main {


    //
    public static void main(String[] args) {
        Main main = new Main();
        main.setup();
    }
    //
    void setup() {

        Filter f1 = new Filter();
        f1.setId("10");
        try {
            String text  = query(f1);
            System.out.println(text);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }


    String query(Filter filter) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {

        StringBuffer stringBuffer = new StringBuffer();
        //获取class
        Class c = filter.getClass();
        boolean isExist = c.isAnnotationPresent(Table.class);
        if (isExist == false) {
            return null;
        }
        Table table = (Table) c.getAnnotation(Table.class);

        String tableName = table.value();
        stringBuffer.append("select * from ").append(tableName).append(" where 1 = 1 ");
        //遍历
        Field[] fields = c.getDeclaredFields();
        for (Field field:fields) {
            boolean iscolum = field.isAnnotationPresent(Column.class);
            if (iscolum == false) {
                continue;
            }

            Column column = field.getAnnotation(Column.class);
            String name = column.value();

            //拿到字段和get方法
            String fieldName = field.getName();
            String getMethodName = "get" + fieldName.substring(0,1).toUpperCase() + fieldName.substring(1);


            //执行method
            Method getMethod = c.getMethod(getMethodName);
            String fieldValue = (String) getMethod.invoke(filter);
            if (fieldValue == null) {
                continue;
            }

            //拼接sql
            stringBuffer.append(" and ").append(fieldName).append(" = ").append(fieldValue);
        }
        return  stringBuffer.toString();
    }
}

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME) 
@interface Column {
    String value();
}

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@interface Table {

    String value();
}