使用注解生成sql语句

// 下面使用注解来生成sql语句
1、先定义2个注解类，Table,Column
2、定义一个JavaBean类
3、编写注解实现类

注解类：Table
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Table {
    String value();
}

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

javaBean类
@Table(value = "USER")
public class UserBean {

    @Column(value = "id")
    private int id;

    @Column(value = "userId")
    private String userId;

    @Column(value = "userName")
    private String userName;

    @Column(value = "email")
    private String email;

    @Column(value = "mobile")
    private String mobile;

    @Column(value = "phone")
    private String phone;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getMobile() {
        return mobile;
    }

    public void setMobile(String mobile) {
        this.mobile = mobile;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }
}



4、注解测试类
public class MainTest {

    public static void main(String[] args) {
        UserBean userBean = new UserBean();
        userBean.setId(10);
        userBean.setEmail("123@qq.com");
        beanSql(userBean);

    }

    public static String beanSql(Object user){
        StringBuffer sql = new StringBuffer();

        Class c = user.getClass();
        boolean flag = c.isAnnotationPresent(Table.class);  // 判断该类是否包含Table的注解，返回true/false
        if(!flag){
            return null;
        }
        Table table = (Table) c.getAnnotation(Table.class); // 获取到注解对象
        String tableName = table.value(); // 获取到注解对象的值
        sql.append("select * from ").append(tableName).append(" where 1=1");
        // 获取该类中字段的注解
        //Field[] fields = c.getFields();
        Field[] fields = c.getDeclaredFields();
        for (int i = 0; i < fields.length; i++) {
            boolean fieldFalg = fields[i].isAnnotationPresent(Column.class);
            if(!fieldFalg){
                continue;
            }
            Column column = fields[i].getAnnotation(Column.class);
            String fieldName = column.value();  // 字段的名称
            Object fieldValue = null ;  // 字段的值
            // 字段的值获取,使用反射
            try {
                // 获取方法名如:getId()
                String methodName = "get"+fieldName.substring(0,1).toUpperCase()+fieldName.substring(1).toString();
                // 通过反射invoke获取到值
                Method method = c.getMethod(methodName);
                fieldValue = method.invoke(user,null);
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }

            if(fieldValue == null || (fieldValue instanceof Integer && (Integer)fieldValue == 0)){
                continue;
            }
            if(fieldValue instanceof String){
                sql.append(" and ").append(fields[i].getName()).append("=‘").append(fieldValue).append("‘");
            }else if(fieldValue instanceof Integer){
                sql.append(" and ").append(fields[i].getName()).append("=").append(fieldValue);
            }
        }
        System.out.println(sql.toString());

        return sql.toString();
    }

}

生成sql如下：
select * from USER where 1=1 and id=10 and email=‘123@qq.com‘；

方法说明：
getAnnotation(Table.class)：检查对象是否带有@Table注解
getFields() ： 获得某个类的所有的公共（public）的字段，包括父类。
getDeclaredFields() ：获得某个类的所有申明的字段，即包括public、private和proteced，但是不包括父类的申明字段
isAnnotationPresent（Table.class）: 指定注释类型的注释存在于此元素上