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#mybatis分页组件实现原理 分页原理很简单，只要实现Mybatis的Interceptor就可以使用，这个组件的作者很给力，写的很详细，就不详细描述了。

Mybatis分页组件实现

#手写组件实现的一个类

@Intercepts({ @Signature(type = Executor.class, method = "query", args = { MappedStatement.class, Object.class,RowBounds.class, ResultHandler.class }) })
public class PaginationStatementInterceptor implements Interceptor {private final static Logger logger = LoggerFactory.getLogger(PaginationStatementInterceptor.class);private Dialect dialect;static int MAPPED_STATEMENT_INDEX = 0;static int PARAMETER_INDEX = 1;static int ROWBOUNDS_INDEX = 2;static int RESULT_HANDLER_INDEX = 3;public Object intercept(Invocation invocation) throws Throwable {final Object[] queryArgs = invocation.getArgs();Object parameter = queryArgs[PARAMETER_INDEX];Pageable pageRequest = findPageableObject(parameter);if (pageRequest != null) {final MappedStatement ms = (MappedStatement) queryArgs[MAPPED_STATEMENT_INDEX];if (parameter instanceof ParamMap) {ParamMap<?> paramMap = (ParamMap<?>) parameter;if (paramMap.size() == 4) {parameter = ((ParamMap<?>) parameter).get("param1");queryArgs[PARAMETER_INDEX] = parameter;}}final BoundSql boundSql = ms.getBoundSql(parameter);String sql = boundSql.getSql().trim().replaceAll(";$", "");int total = this.queryTotal(sql, ms, boundSql);if (pageRequest.getSort() != null) {Iterator<Order> it = pageRequest.getSort().iterator();if (it.hasNext()) {sql = "select o.* from ( " + sql + " ) o order by ";}for (int i = 0; it.hasNext(); i++) {if (i > 0) {sql += " , ";}Order order = it.next();sql += order.getProperty() + " " + order.getDirection().name();}}String limitSql = dialect.getLimitString(sql, pageRequest.getOffset(), pageRequest.getPageSize());queryArgs[ROWBOUNDS_INDEX] = new RowBounds(RowBounds.NO_ROW_OFFSET, RowBounds.NO_ROW_LIMIT);queryArgs[MAPPED_STATEMENT_INDEX] = copyFromNewSql(ms, boundSql, limitSql);Object ret = invocation.proceed();@SuppressWarnings("unchecked")Page<Object> page = new PageImpl<Object>((List<Object>) ret, pageRequest, total);List<Page<?>> ls = new ArrayList<Page<?>>(1);ls.add(page);return ls;}return invocation.proceed();}public Object plugin(Object target) {return Plugin.wrap(target, this);}public void setProperties(Properties properties) {String dialectClass = properties.getProperty("dialectClass");try {setDialect((Dialect) Class.forName(dialectClass).newInstance());} catch (Exception e) {throw new RuntimeException("cannot create dialect instance by dialectClass:" + dialectClass, e);}}public Dialect getDialect() {return dialect;}public void setDialect(Dialect dialect) {this.dialect = dialect;}private Pageable findPageableObject(Object params) {if (params == null) {return null;}// 单个参数 表现为参数对象if (Pageable.class.isAssignableFrom(params.getClass())) {return (Pageable) params;}// 多个参数 表现为 ParamMapelse if (params instanceof ParamMap) {ParamMap<?> paramMap = (ParamMap<?>) params;for (Map.Entry<String, ?> entry : paramMap.entrySet()) {Object paramValue = entry.getValue();if (paramValue != null && Pageable.class.isAssignableFrom(paramValue.getClass())) {return (Pageable) paramValue;}}}return null;}private int queryTotal(String sql, MappedStatement mappedStatement, BoundSql boundSql) throws SQLException {Connection connection = null;PreparedStatement countStmt = null;ResultSet rs = null;try {connection = mappedStatement.getConfiguration().getEnvironment().getDataSource().getConnection();String countSql = /** "select count(1) as cnt from (" + sql + ")  c";*/ this.dialect.getCountString(sql);countStmt = connection.prepareStatement(countSql);BoundSql countBoundSql = new BoundSql(mappedStatement.getConfiguration(), countSql,boundSql.getParameterMappings(), boundSql.getParameterObject());setParameters(countStmt, mappedStatement, countBoundSql, boundSql.getParameterObject());rs = countStmt.executeQuery();int totalCount = 0;if (rs.next()) {totalCount = rs.getInt(1);}return totalCount;} catch (SQLException e) {logger.error("查询总记录数出错", e);throw e;} finally {if (rs != null) {try {rs.close();} catch (SQLException e) {logger.error("exception happens when doing: ResultSet.close()", e);}}if (countStmt != null) {try {countStmt.close();} catch (SQLException e) {logger.error("exception happens when doing: PreparedStatement.close()", e);}}if (connection != null) {try {connection.close();} catch (SQLException e) {logger.error("exception happens when doing: Connection.close()", e);}}}}private void setParameters(PreparedStatement ps, MappedStatement mappedStatement, BoundSql boundSql,Object parameterObject) throws SQLException {ParameterHandler parameterHandler = /** mappedStatement.getLang().* createParameterHandler(* mappedStatement, parameterObject,* boundSql);*/new DefaultParameterHandler(mappedStatement, parameterObject, boundSql);parameterHandler.setParameters(ps);}private MappedStatement copyFromNewSql(MappedStatement ms, BoundSql boundSql, String sql) {BoundSql newBoundSql = copyFromBoundSql(ms, boundSql, sql);return copyFromMappedStatement(ms, new BoundSqlSqlSource(newBoundSql));}public static class BoundSqlSqlSource implements SqlSource {BoundSql boundSql;public BoundSqlSqlSource(BoundSql boundSql) {this.boundSql = boundSql;}public BoundSql getBoundSql(Object parameterObject) {return boundSql;}}private BoundSql copyFromBoundSql(MappedStatement ms, BoundSql boundSql, String sql) {BoundSql newBoundSql = new BoundSql(ms.getConfiguration(), sql, boundSql.getParameterMappings(),boundSql.getParameterObject());for (ParameterMapping mapping : boundSql.getParameterMappings()) {String prop = mapping.getProperty();if (boundSql.hasAdditionalParameter(prop)) {newBoundSql.setAdditionalParameter(prop, boundSql.getAdditionalParameter(prop));}}return newBoundSql;}// see: MapperBuilderAssistantprivate MappedStatement copyFromMappedStatement(MappedStatement ms, SqlSource newSqlSource) {Builder builder = new 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) {StringBuffer keyProperties = new StringBuffer();for (String keyProperty : ms.getKeyProperties()) {keyProperties.append(keyProperty).append(",");}keyProperties.delete(keyProperties.length() - 1, keyProperties.length());builder.keyProperty(keyProperties.toString());}// setStatementTimeout()builder.timeout(ms.getTimeout());// setStatementResultMap()builder.parameterMap(ms.getParameterMap());// setStatementResultMap()builder.resultMaps(ms.getResultMaps());builder.resultSetType(ms.getResultSetType());// setStatementCache()builder.cache(ms.getCache());builder.flushCacheRequired(ms.isFlushCacheRequired());builder.useCache(ms.isUseCache());return builder.build();}
}

如何使用，这个手写的分页组件

在你的Mapper类中，需要分页的接口里加入分页参数Pageable pageable，然后mapper.xml中就不需要写limit 0，10等语句，在执行分页查询前，组件会自动组装分页

        Page<BaseType> queryBaseTypePageList(Map<String,Object> map,Pageable pageable);

#推荐一款非好用的Mybatis分页组件 该 @Liuzh_533 作者的项目，非常好推荐一下。 GIT地址：https://github.com/pagehelper/Mybatis-PageHelper