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MyBatis插件机制揭秘：从拦截器开发到分页插件实战

news 2025/7/13 3:49:09

一、拦截器体系架构解析

1.1 责任链模式在MyBatis中的实现

MyBatis通过动态代理技术构建拦截器链，每个插件相当于一个切面：

// 拦截器链构建过程
public class InterceptorChain {private final List<Interceptor> interceptors = new ArrayList<>();public Object pluginAll(Object target) {for (Interceptor interceptor : interceptors) {target = interceptor.plugin(target);}return target;}
}

1.2 核心接口与注解体系

Interceptor接口定义：

public interface Interceptor {Object intercept(Invocation invocation) throws Throwable;Object plugin(Object target);void setProperties(Properties properties);
}

注解配置示例：

@Intercepts({@Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class}),@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})
public class MyInterceptor implements Interceptor {// 实现方法
}

二、关键拦截点详解

2.1 四大核心拦截点

拦截点类型	典型应用场景	执行时机
Executor	事务管理、性能监控	SQL执行前
ParameterHandler	参数加密、特殊字符处理	参数绑定时
ResultSetHandler	结果集脱敏、自动类型转换	结果映射时
StatementHandler	SQL重写、分页处理	SQL生成后

2.2 拦截点选择策略

分页插件拦截点选择：

@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})
public class PaginationInterceptor implements Interceptor {// 实现分页SQL改写
}

三、分页插件开发实战

3.1 插件架构设计

3.2 核心代码实现

分页拦截器实现：

public class PageInterceptor implements Interceptor {@Overridepublic Object intercept(Invocation invocation) throws Throwable {StatementHandler statementHandler = (StatementHandler) invocation.getTarget();BoundSql boundSql = statementHandler.getBoundSql();String originalSql = boundSql.getSql();// 获取分页参数Page page = (Page) boundSql.getParameterObject();int offset = (page.getPageNum() - 1) * page.getPageSize();String pageSql = originalSql + " LIMIT " + offset + ", " + page.getPageSize();// 反射修改SQLMetaObject metaObject = SystemMetaObject.forObject(boundSql);metaObject.setValue("sql", pageSql);return invocation.proceed();}
}

3.3 插件配置与使用

MyBatis配置：

<!-- mybatis-config.xml -->
<plugins><plugin interceptor="com.example.interceptor.PageInterceptor"><property name="dialect" value="mysql"/></plugin>
</plugins>

Java代码使用：

// 分页查询示例
Page page = new Page(1, 10);
List<User> users = sqlSession.selectList("UserMapper.selectAll", page);

四、高级主题与优化

4.1 多数据库适配方案

方言配置策略：

public class DialectResolver {private static final Map<String, String> dialectMap = new HashMap<>();static {dialectMap.put("mysql", "LIMIT %d,%d");dialectMap.put("oracle", "ROWNUM <= %d AND ROWNUM > %d");}public static String resolve(String dialect, int offset, int limit) {String pattern = dialectMap.get(dialect);return String.format(pattern, offset, limit);}
}

4.2 性能优化技巧

SQL缓存：缓存修改后的分页SQL，减少反射开销
参数预处理：使用MetaObject的set方法替代反射
异步日志：非核心路径使用异步日志记录

4.3 插件调试技巧

日志配置建议：

# log4j2.properties
log4j2.logger.mybatis.interceptor=DEBUG, console

调试输出示例：

2025-07-10 15:30:45 DEBUG [PageInterceptor] Original SQL: SELECT * FROM user
2025-07-10 15:30:45 DEBUG [PageInterceptor] Modified SQL: SELECT * FROM user LIMIT 0,10