MyBatis实现动态SQL更新的代码示例

@Component
@Slf4j
@Intercepts({
        @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})
public class DynamicSqlInterceptor implements Interceptor {
 ...
}

# 动态sql配置
dynamicSql:
  placeholder: "@dynamicSql"
  date: "2023-07-10 20:10:30"

public interface DynamicSqlMapper {
    @DynamicSql
    Long count();
}

<mapper namespace="ltd.newbee.mall.core.dao.DynamicSqlMapper">
    <select id="count" resultType="java.lang.Long">
        select count(1) from member
        where create_time > @dynamicSql
    </select>
</mapper>

@Component
@Slf4j
@Intercepts({
        @Signature(type = StatementHandler.class, 
                method = "prepare", args = {Connection.class, Integer.class})
})
public class DynamicSqlInterceptor implements Interceptor {
    @Value("${dynamicSql.placeholder}")
    private String placeholder;
    @Value("${dynamicSql.date}")
    private  String dynamicDate;
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        // 1. 获取 StatementHandler 对象也就是执行语句
        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
        // 2. MetaObject 是 MyBatis 提供的一个反射帮助类，可以优雅访问对象的属性，这里是对 statementHandler 对象进行反射处理，
        MetaObject metaObject = MetaObject.forObject(statementHandler, SystemMetaObject.DEFAULT_OBJECT_FACTORY,
                SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,
                        new DefaultReflectorFactory());
        // 3. 通过 metaObject 反射获取 statementHandler 对象的成员变量 mappedStatement
        MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("delegate.mappedStatement");
        // mappedStatement 对象的 id 方法返回执行的 mapper 方法的全路径名，如ltd.newbee.mall.core.dao.UserMapper.insertUser
        String id = mappedStatement.getId();
        // 4. 通过 id 获取到 Dao 层类的全限定名称，然后反射获取 Class 对象
        Class<?> classType = Class.forName(id.substring(0, id.lastIndexOf(".")));
        // 5. 获取包含原始 sql 语句的 BoundSql 对象
        BoundSql boundSql = statementHandler.getBoundSql();
        String sql = boundSql.getSql();
        log.info("替换前---sql：{}", sql);
        // 拦截方法
        String mSql = null;
        // 6. 遍历 Dao 层类的方法
        for (Method method : classType.getMethods()) {
            // 7. 判断方法上是否有 DynamicSql 注解，有的话，就认为需要进行 sql 替换
            if (method.isAnnotationPresent(DynamicSql.class)) {
                mSql = sql.replaceAll(placeholder, String.format("'%s'", dynamicDate));
                break;
            }
        }
        if (StringUtils.isNotBlank(mSql)) {
            log.info("替换后---mSql：{}", mSql);
            // 8. 对 BoundSql 对象通过反射修改 SQL 语句。
            Field field = boundSql.getClass().getDeclaredField("sql");
            field.setAccessible(true);
            field.set(boundSql, mSql);
        }
        // 9. 执行修改后的 SQL 语句。
        return invocation.proceed();
    }
    @Override
    public Object plugin(Object target) {
        // 使用 Plugin.wrap 方法生成代理对象
        return Plugin.wrap(target, this);
    }
    @Override
    public void setProperties(Properties properties) {
        // 获取配置文件中的属性值
    }
}

// 测试类
@SpringBootTest
@RunWith(SpringRunner.class)
public class DynamicTest {
    @Autowired
    private DynamicSqlMapper dynamicSqlMapper;
    @Test
    public void test() {
        Long count = dynamicSqlMapper.count();
        Assert.notNull(count, "count不能为null");
    }
}

2023-07-11 22:13:33.375 [main] INFO  l.n.m.config.DynamicSqlInterceptor - [intercept,52] - 替换前---sql：select count(1) from member
        where create_time > @dynamicSql
2023-07-11 22:13:33.376 [main] INFO  l.n.m.config.DynamicSqlInterceptor - [intercept,62] - 替换后---mSql：select count(1) from member
        where create_time > '2023-07-10 20:10:30'