mybatis之分页plugin

mybatis官方提供只能能拦截Executor、ParameterHandler、StatementHandler、ResultSetHandler

Executor:MyBatis执行器，是MyBatis 调度的核心，负责SQL语句的生成和查询缓存的维护

ParameterHandler:负责对用户传递的参数转换成JDBC Statement 所需要的参数

StatementHandler:封装了JDBC Statement操作，负责对JDBC statement 的操作，如设置参数、 将Statement结果集转换成List集合

ResultSetHandler:负责将JDBC返回的ResultSet结果集对象转换成List类型的集合

例：mybatisPlus PaginationInterceptor 分页插件

@Intercepts({@Signature(
    type = StatementHandler.class,
    method = "prepare",
    args = {Connection.class, Integer.class}
)})
public class PaginationInterceptor extends AbstractSqlParserHandler implements Interceptor {

protected static final Log logger = LogFactory.getLog(PaginationInterceptor.class);
    protected ISqlParser countSqlParser;
    protected boolean overflow = false;
    protected long limit = 500L;
    protected String dialectType;
    protected String dialectClazz;

    public PaginationInterceptor() {
    }

    public static String concatOrderBy(String originalSql, IPage page) {
        if (CollectionUtils.isNotEmpty(page.orders())) {
            try {
                List orderList = page.orders();
                Select selectStatement = (Select)CCJSqlParserUtil.parse(originalSql);
                List orderByElements;
                List orderByElementsReturn;
                if (selectStatement.getSelectBody() instanceof PlainSelect) {
                    PlainSelect plainSelect = (PlainSelect)selectStatement.getSelectBody();
                    orderByElements = plainSelect.getOrderByElements();
                    orderByElementsReturn = addOrderByElements(orderList, orderByElements);
                    plainSelect.setOrderByElements(orderByElementsReturn);
                    return plainSelect.toString();
                }

                if (selectStatement.getSelectBody() instanceof SetOperationList) {
                    SetOperationList setOperationList = (SetOperationList)selectStatement.getSelectBody();
                    orderByElements = setOperationList.getOrderByElements();
                    orderByElementsReturn = addOrderByElements(orderList, orderByElements);
                    setOperationList.setOrderByElements(orderByElementsReturn);
                    return setOperationList.toString();
                }

                if (selectStatement.getSelectBody() instanceof WithItem) {
                    return originalSql;
                }

                return originalSql;
            } catch (JSQLParserException var7) {
                logger.warn("failed to concat orderBy from IPage, exception=" + var7.getMessage());
            }
        }

        return originalSql;
    }

    private static List addOrderByElements(List orderList, List orderByElements) {
        List orderByElements = CollectionUtils.isEmpty(orderByElements) ? new ArrayList(orderList.size()) : orderByElements;
        List orderByElementList = (List)orderList.stream().filter((item) -> {
            return StringUtils.isNotBlank(item.getColumn());
        }).map((item) -> {
            OrderByElement element = new OrderByElement();
            element.setExpression(new Column(item.getColumn()));
            element.setAsc(item.isAsc());
            return element;
        }).collect(Collectors.toList());
        ((List)orderByElements).addAll(orderByElementList);
        return (List)orderByElements;
    }

    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler statementHandler = (StatementHandler)PluginUtils.realTarget(invocation.getTarget());
        MetaObject metaObject = SystemMetaObject.forObject(statementHandler);
        this.sqlParser(metaObject);
        MappedStatement mappedStatement = (MappedStatement)metaObject.getValue("delegate.mappedStatement");
        if (SqlCommandType.SELECT == mappedStatement.getSqlCommandType() && StatementType.CALLABLE != mappedStatement.getStatementType()) {
            BoundSql boundSql = (BoundSql)metaObject.getValue("delegate.boundSql");
            Object paramObj = boundSql.getParameterObject();
            IPage page = null;
            if (paramObj instanceof IPage) {
                page = (IPage)paramObj;
            } else if (paramObj instanceof Map) {
                Iterator var8 = ((Map)paramObj).values().iterator();

                while(var8.hasNext()) {
                    Object arg = var8.next();
                    if (arg instanceof IPage) {
                        page = (IPage)arg;
                        break;
                    }
                }
            }

            if (null != page && page.getSize() >= 0L) {
                if (this.limit > 0L && this.limit <= page.getSize()) {
                    this.handlerLimit(page);
                }

                String originalSql = boundSql.getSql();
                Connection connection = (Connection)invocation.getArgs()[0];
                DbType dbType = StringUtils.isNotBlank(this.dialectType) ? DbType.getDbType(this.dialectType) : JdbcUtils.getDbType(connection.getMetaData().getURL());
                if (page.isSearchCount()) {
                    SqlInfo sqlInfo = SqlParserUtils.getOptimizeCountSql(page.optimizeCountSql(), this.countSqlParser, originalSql);
                    this.queryTotal(sqlInfo.getSql(), mappedStatement, boundSql, page, connection);
                    if (page.getTotal() <= 0L) {
                        return null;
                    }
                }

                String buildSql = concatOrderBy(originalSql, page);
                DialectModel model = DialectFactory.buildPaginationSql(page, buildSql, dbType, this.dialectClazz);
                Configuration configuration = mappedStatement.getConfiguration();
                List mappings = new ArrayList(boundSql.getParameterMappings());
                Map additionalParameters = (Map)metaObject.getValue("delegate.boundSql.additionalParameters");
                model.consumers(mappings, configuration, additionalParameters);
                metaObject.setValue("delegate.boundSql.sql", model.getDialectSql());
                metaObject.setValue("delegate.boundSql.parameterMappings", mappings);
                return invocation.proceed();
            } else {
                return invocation.proceed();
            }
        } else {
            return invocation.proceed();
        }
    }

    protected void handlerLimit(IPage page) {
        page.setSize(this.limit);
    }

    protected void queryTotal(String sql, MappedStatement mappedStatement, BoundSql boundSql, IPage page, Connection connection) {
        try {
            PreparedStatement statement = connection.prepareStatement(sql);
            Throwable var7 = null;

            try {
                DefaultParameterHandler parameterHandler = new MybatisDefaultParameterHandler(mappedStatement, boundSql.getParameterObject(), boundSql);
                parameterHandler.setParameters(statement);
                long total = 0L;
                ResultSet resultSet = statement.executeQuery();
                Throwable var12 = null;

                try {
                    if (resultSet.next()) {
                        total = resultSet.getLong(1);
                    }
                } catch (Throwable var37) {
                    var12 = var37;
                    throw var37;
                } finally {
                    if (resultSet != null) {
                        if (var12 != null) {
                            try {
                                resultSet.close();
                            } catch (Throwable var36) {
                                var12.addSuppressed(var36);
                            }
                        } else {
                            resultSet.close();
                        }
                    }

                }

                page.setTotal(total);
                if (this.overflow && page.getCurrent() > page.getPages()) {
                    this.handlerOverflow(page);
                }
            } catch (Throwable var39) {
                var7 = var39;
                throw var39;
            } finally {
                if (statement != null) {
                    if (var7 != null) {
                        try {
                            statement.close();
                        } catch (Throwable var35) {
                            var7.addSuppressed(var35);
                        }
                    } else {
                        statement.close();
                    }
                }

            }

        } catch (Exception var41) {
            throw ExceptionUtils.mpe("Error: Method queryTotal execution error of sql : \n %s \n", var41, new Object[]{sql});
        }
    }

    protected void handlerOverflow(IPage page) {
        page.setCurrent(1L);
    }

    public Object plugin(Object target) {
        return target instanceof StatementHandler ? Plugin.wrap(target, this) : target;
    }

    public void setProperties(Properties prop) {
        String dialectType = prop.getProperty("dialectType");
        String dialectClazz = prop.getProperty("dialectClazz");
        if (StringUtils.isNotBlank(dialectType)) {
            this.dialectType = dialectType;
        }

        if (StringUtils.isNotBlank(dialectClazz)) {
            this.dialectClazz = dialectClazz;
        }

    }

    public PaginationInterceptor setCountSqlParser(final ISqlParser countSqlParser) {
        this.countSqlParser = countSqlParser;
        return this;
    }

    public PaginationInterceptor setOverflow(final boolean overflow) {
        this.overflow = overflow;
        return this;
    }

    public PaginationInterceptor setLimit(final long limit) {
        this.limit = limit;
        return this;
    }

    public PaginationInterceptor setDialectType(final String dialectType) {
        this.dialectType = dialectType;
        return this;
    }

    public PaginationInterceptor setDialectClazz(final String dialectClazz) {
        this.dialectClazz = dialectClazz;
        return this;
    }
}