01、Mybatis-Plus入门 - MybatisPlus插件简介
Mybatis插件
Mybatis插件，实际上就是一个拦截器，应用代理模式，在方法级别上进行拦截。可以实现分页、SQL打印监控、公共字段赋值等功能，基本上可以控制SQL执行的各个阶段，如执行阶段，参数处理阶段，语法构建阶段，结果集处理阶段，具体可以根据项目业务来实现对应业务逻辑。
public interface Interceptor {
// 可从Invocation参数中拿到执行方法的对象，方法，方法参数，从而实现各种业务逻辑
Object intercept(Invocation invocation) throws Throwable;
// 生成代理对象
default Object plugin(Object target) {
return Plugin.wrap(target, this);
}
// 设置一些属性变量
default void setProperties(Properties properties) {
// NOP
}
}
MybatisPlus插件
plus提供了InnerInterceptor来实现插件功能，已经提供了很多插件使用，我们可以通过添加直接使用，也可以自己实现InnerInterceptor，然后通过MybatisPlusInterceptor添加插件来使用。
目前已有的功能:
- 自动分页: PaginationInnerInterceptor
- 多租户: TenantLineInnerInterceptor
- 动态表名: DynamicTableNameInnerInterceptor
- 乐观锁: OptimisticLockerInnerInterceptor
- sql性能规范: IllegalSQLInnerInterceptor
- 防止全表更新与删除: BlockAttackInnerInterceptor
- 数据权限：DataPermissionInterceptor
@SuppressWarnings({
"rawtypes"})
public interface InnerInterceptor {
/**
* 判断是否执行 {@link Executor#query(MappedStatement, Object, RowBounds, ResultHandler, CacheKey, BoundSql)}
* <p>
* 如果不执行query操作,则返回 {@link Collections#emptyList()}
*
* @param executor Executor(可能是代理对象)
* @param ms MappedStatement
* @param parameter parameter
* @param rowBounds rowBounds
* @param resultHandler resultHandler
* @param boundSql boundSql
* @return 新的 boundSql
*/
default boolean willDoQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
return true;
}
/**
* {@link Executor#query(MappedStatement, Object, RowBounds, ResultHandler, CacheKey, BoundSql)} 操作前置处理
* <p>
* 改改sql啥的
*
* @param executor Executor(可能是代理对象)
* @param ms MappedStatement
* @param parameter parameter
* @param rowBounds rowBounds
* @param resultHandler resultHandler
* @param boundSql boundSql
*/
default void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
// do nothing
}
/**
* 判断是否执行 {@link Executor#update(MappedStatement, Object)}
* <p>
* 如果不执行update操作,则影响行数的值为 -1
*
* @param executor Executor(可能是代理对象)
* @param ms MappedStatement
* @param parameter parameter
*/
default boolean willDoUpdate(Executor executor, MappedStatement ms, Object parameter) throws SQLException {
return true;
}
/**
* {@link Executor#update(MappedStatement, Object)} 操作前置处理
* <p>
* 改改sql啥的
*
* @param executor Executor(可能是代理对象)
* @param ms MappedStatement
* @param parameter parameter
*/
default void beforeUpdate(Executor executor, MappedStatement ms, Object parameter) throws SQLException {
// do nothing
}
/**
* {@link StatementHandler#prepare(Connection, Integer)} 操作前置处理
* <p>
* 改改sql啥的
*
* @param sh StatementHandler(可能是代理对象)
* @param connection Connection
* @param transactionTimeout transactionTimeout
*/
default void beforePrepare(StatementHandler sh, Connection connection, Integer transactionTimeout) {
// do nothing
}
default void setProperties(Properties properties) {
// do nothing
}
}
@Intercepts(
{
@Signature(type = StatementHandler.class, method = "prepare", args = {
Connection.class, Integer.class}),
@Signature(type = Executor.class, method = "update", args = {
MappedStatement.class, Object.class}),
@Signature(type = Executor.class, method = "query", args = {
MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}),
@Signature(type = Executor.class, method = "query", args = {
MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class}),
}
)
public class MybatisPlusInterceptor implements Interceptor {
@Setter
private List<InnerInterceptor> interceptors = new ArrayList<>();
@Override
public Object intercept(Invocation invocation) throws Throwable {
Object target = invocation.getTarget();
Object[] args = invocation.getArgs();
if (target instanceof Executor) {
final Executor executor = (Executor) target;
Object parameter = args[1];
boolean isUpdate = args.length == 2;
MappedStatement ms = (MappedStatement) args[0];
if (!isUpdate && ms.getSqlCommandType() == SqlCommandType.SELECT) {
RowBounds rowBounds = (RowBounds) args[2];
ResultHandler resultHandler = (ResultHandler) args[3];
BoundSql boundSql;
if (args.length == 4) {
boundSql = ms.getBoundSql(parameter);
} else {
// 几乎不可能走进这里面,除非使用Executor的代理对象调用query[args[6]]
boundSql = (BoundSql) args[5];
}
for (InnerInterceptor query : interceptors) {
if (!query.willDoQuery(executor, ms, parameter, rowBounds, resultHandler, boundSql)) {
return Collections.emptyList();
}
query.beforeQuery(executor, ms, parameter, rowBounds, resultHandler, boundSql);
}
CacheKey cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);
return executor.query(ms, parameter, rowBounds, resultHandler, cacheKey, boundSql);
} else if (isUpdate) {
for (InnerInterceptor update : interceptors) {
if (!update.willDoUpdate(executor, ms, parameter)) {
return -1;
}
update.beforeUpdate(executor, ms, parameter);
}
}
} else {
// StatementHandler
final StatementHandler sh = (StatementHandler) target;
Connection connections = (Connection) args[0];
Integer transactionTimeout = (Integer) args[1];
for (InnerInterceptor innerInterceptor : interceptors) {
innerInterceptor.beforePrepare(sh, connections, transactionTimeout);
}
}
return invocation.proceed();
}
@Override
public Object plugin(Object target) {
if (target instanceof Executor || target instanceof StatementHandler) {
return Plugin.wrap(target, this);
}
return target;
}
public void addInnerInterceptor(InnerInterceptor innerInterceptor) {
this.interceptors.add(innerInterceptor);
}
public List<InnerInterceptor> getInterceptors() {
return Collections.unmodifiableList(interceptors);
}
/**
* 使用内部规则,拿分页插件举个栗子:
* <p>
* - key: "@page" ,value: "com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor"
* - key: "page:limit" ,value: "100"
* <p>
* 解读1: key 以 "@" 开头定义了这是一个需要组装的 InnerInterceptor, 以 "page" 结尾表示别名
* value 是 InnerInterceptor 的具体的 class 全名
* 解读2: key 以上面定义的 "别名 + ':'" 开头指这个 value 是定义的该 InnerInterceptor 属性需要设置的值
* <p>
* 如果这个 InnerInterceptor 不需要配置属性也要加别名
*/
@Override
public void setProperties(Properties properties) {
PropertyMapper pm = PropertyMapper.newInstance(properties);
Map<String, Properties> group = pm.group("@");
group.forEach((k, v) -> {
InnerInterceptor innerInterceptor = ClassUtils.newInstance(k);
innerInterceptor.setProperties(v);
addInnerInterceptor(innerInterceptor);
});
}
}