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插件（plugins）

MyBatis 允许你在映射语句执行过程中的某一点进行拦截调用。默认情况下，MyBatis 允许使用插件来拦截的方法调用包括：

• Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
• ParameterHandler (getParameterObject, setParameters)
• ResultSetHandler (handleResultSets, handleOutputParameters)
• StatementHandler (prepare, parameterize, batch, update, query)

通过 MyBatis 提供的强大机制，使用插件是非常简单的，只需实现 Interceptor 接口，并指定想要拦截的方法签名即可。

/**
 * 默认情况下，MyBatis 允许使用插件来拦截的方法调用包括：
 *
 * Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
 * ParameterHandler (getParameterObject, setParameters)
 * ResultSetHandler (handleResultSets, handleOutputParameters)
 * StatementHandler (prepare, parameterize, batch, update, query)
 */
@Slf4j
@Intercepts({
        // method = "query"拦截select方法、而method = "update"则能拦截insert、update、delete的方法
        @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})
})
// 只需实现 Interceptor 接口，并指定想要拦截的方法签名即可
public class MybatisInterceptorPlugin implements Interceptor {
    //需要处理的表
    private static final List<String> TABLE_LIST = Arrays.asList("model_meta");
    
    // 1.通过Invocation中的args变量。我们能拿到MappedStatement这个对象（args[0]），传入sql语句的参数Object (args[1])。
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        final Object[] args = invocation.getArgs();
        // 获取 MappedStatement对象 和 参数对象
        MappedStatement ms = (MappedStatement) args[0];
        Object parameterObject = args[1];

        // sql命令类型
        SqlCommandType sqlCommandType = ms.getSqlCommandType();
        
        try {
            switch (sqlCommandType) {
                case INSERT:
                    tableName = args[1].getClass().getAnnotation(Table.class).name();
                    if (!TABLE_LIST.contains(tableName)) {
                        return invocation.proceed();
                    }
                    // 自己的业务操作
                    break;
                case UPDATE:
                    Field table = Example.class.getDeclaredField("table");
                    table.setAccessible(true);
                    tableName = ((EntityTable) table.get(((MapperMethod.ParamMap) args[1]).get("example"))).getName();
                    if(!checkUpdateParam(args[1])) {
                        return invocation.proceed();
                    }
                    if (!TABLE_LIST.contains(tableName)) {
                        return invocation.proceed();
                    }
                    break;
                case SELECT:
                    // 2. sqlSource对象和传入sql语句的参数对象Object就能获得BoundSql。BoundSql的toString方法就能获取到有占位符的sql语句了，我们的业务逻辑就能在这里介入。
                    // 获取预编译sql对象
                    BoundSql boundSql = ms.getBoundSql(parameterObject);
                    // 获取到拥有占位符的sql语句
                    String sql = boundSql.getSql();
                    SQLExprTableSource sqlTableSource = getTableNameBySql(sql);
                    if(sqlTableSource == null) {
                        break;
                    }
                    tableName = sqlTableSource.toString();
                    if (!TABLE_LIST.contains(tableName)) {
                        break;
                    }
                    // 3.获取到sql语句，根据规则替换表名，塞回BoundSql对象中、再把BoundSql对象塞回MappedStatement对象中。最后再赋值给args[0]（实际被拦截方法所需的参数）就搞定了
                    String newSql = sql.replace(tableName, tableName + "_publish_view");
                    //重新生成一个BoundSql对象
                    BoundSql bs = new BoundSql(ms.getConfiguration(), newSql, boundSql.getParameterMappings(), parameterObject);
                    // start 解决There is no getter for property named '__frch_criterion_1' in 报错
                    for (ParameterMapping parameterMapping : boundSql.getParameterMappings()) {
                        String property = parameterMapping.getProperty();
                        if (boundSql.hasAdditionalParameter(property)) {
                            bs.setAdditionalParameter(property, boundSql.getAdditionalParameter(property));
                        }
                    }
                    // end 解决There is no getter for property named '__frch_criterion_1' in 报错
                    //重新生成一个MappedStatement对象
                    MappedStatement newMs = copyMappedStatement(ms, new BoundSqlSqlSource(bs));
                    //赋回给实际执行方法所需的参数中
                    args[0] = newMs;
                default:
                    break;
            }

        } catch (Exception e) {
            log.error("拦截,invocation:{}", invocation.toString(), e);
        }
        return invocation.proceed();
    }

    public static SQLExprTableSource getTableNameBySql(String sql) {
        MySqlStatementParser mySqlStatementParser = new MySqlStatementParser(sql);
        SQLStatement statement = mySqlStatementParser.parseStatement();
        SQLExprTableSource sqlTableSource = null;
        if(statement instanceof SQLSelectStatement){
            SQLSelect selectQuery = ((SQLSelectStatement)statement).getSelect();
            MySqlSelectQueryBlock sqlSelectQuery = (MySqlSelectQueryBlock)selectQuery.getQuery();
            sqlTableSource = (SQLExprTableSource)sqlSelectQuery.getFrom();
            // 可以获取where条件对象 SQLBinaryOpExpr
            // selectList
        }else if(statement instanceof SQLInsertStatement){
            SQLInsertStatement sqlInsertStatement = (SQLInsertStatement)statement;
            sqlTableSource = sqlInsertStatement.getTableSource();
        }else if(statement instanceof SQLUpdateStatement){
            SQLUpdateStatement sqlUpdateStatement = (SQLUpdateStatement)statement;
            sqlTableSource = (SQLExprTableSource)sqlUpdateStatement.getTableSource();
        }else if(statement instanceof SQLDeleteStatement){
            SQLDeleteStatement sqlUpdateStatement = (SQLDeleteStatement)statement;
            sqlTableSource = (SQLExprTableSource)sqlUpdateStatement.getTableSource();
        }

        return sqlTableSource;
    }

    /***
     * 复制一个新的MappedStatement
     * @param ms
     * @param newSqlSource
     * @return
     */
    private MappedStatement copyMappedStatement (MappedStatement ms, SqlSource newSqlSource) {
        MappedStatement.Builder builder = new MappedStatement.Builder(ms.getConfiguration(), ms.getId(), newSqlSource, ms.getSqlCommandType());

        builder.resource(ms.getResource());
        builder.fetchSize(ms.getFetchSize());
        builder.statementType(ms.getStatementType());
        builder.keyGenerator(ms.getKeyGenerator());
        if (ms.getKeyProperties() != null && ms.getKeyProperties().length > 0) {
            builder.keyProperty(String.join(",",ms.getKeyProperties()));
        }
        builder.timeout(ms.getTimeout());
        builder.parameterMap(ms.getParameterMap());
        builder.resultMaps(ms.getResultMaps());
        builder.resultSetType(ms.getResultSetType());
        builder.cache(ms.getCache());
        builder.flushCacheRequired(ms.isFlushCacheRequired());
        builder.useCache(ms.isUseCache());
        return builder.build();
    }

    /**
     * MappedStatement构造器接受的是SqlSource
     * 实现SqlSource接口，将BoundSql封装进去
     */
    public static class BoundSqlSqlSource implements SqlSource {
        private BoundSql boundSql;
        public BoundSqlSqlSource(BoundSql boundSql) {
            this.boundSql = boundSql;
        }
        @Override
        public BoundSql getBoundSql(Object parameterObject) {
            return boundSql;
        }
    }
}

@Configuration
@ConditionalOnBean({SqlSessionFactory.class})
public class MybatisConfig {

    @Autowired
    private List<SqlSessionFactory> sqlSessionFactoryList;

    @PostConstruct
    public void envInterceptor() {
        MybatisInterceptorPlugin envInterceptor = new MybatisInterceptorPlugin();
        for (SqlSessionFactory sqlSessionFactory : sqlSessionFactoryList) {
            sqlSessionFactory.getConfiguration().addInterceptor(envInterceptor);
        }
    }
}