Mybatis封装分页查询的java公用类

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  直接上分页公共代码，其实现的原理是使用了拦截器的拦截作用。拦截一类分页查询的请求。我们根据传进来的参数是否是需要interceptor()方法中拦截的参数，是的话则拦截，并执行相应的SQL追加，否则，不进行追加。直接放行。视作普通查询。      需要在Mybatis的配置文件中配置加载服务器的时候加载该公共类:mybatis-config.xml     <?xml version="1.0" encoding="UTF-8"?>        <!DOCTYPE configuration        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"       "http://mybatis.org/dtd/mybatis-3-config.dtd">        <configuration>                 <properties></properties>                <plugins>                        <plugin interceptor="com.iboxpay.clear.filter.PaginationInterceptor"></plugin>               </plugins>       </configuration>
import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.util.Properties;    
import org.apache.ibatis.executor.parameter.ParameterHandler; import org.apache.ibatis.executor.statement.StatementHandler;     import org.apache.ibatis.mapping.BoundSql;     import org.apache.ibatis.mapping.MappedStatement; import org.apache.ibatis.plugin.Interceptor;     import org.apache.ibatis.plugin.Intercepts;     import org.apache.ibatis.plugin.Invocation;     import org.apache.ibatis.plugin.Plugin;     import org.apache.ibatis.plugin.Signature;     import org.apache.ibatis.reflection.MetaObject;     import org.apache.ibatis.reflection.factory.DefaultObjectFactory; import org.apache.ibatis.reflection.factory.ObjectFactory; import org.apache.ibatis.reflection.wrapper.DefaultObjectWrapperFactory; import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory; import org.apache.ibatis.scripting.defaults.DefaultParameterHandler; import org.apache.ibatis.session.RowBounds; import org.slf4j.Logger; import org.slf4j.LoggerFactory;
/**  * 分页拦截器  * @since 10.20.2014  */ @Intercepts({@Signature(type=StatementHandler.class,method="prepare",args={Connection.class})})     public class PaginationInterceptor implements Interceptor {          private final Logger logger = LoggerFactory.getLogger(PaginationInterceptor.class);
    private static final ObjectFactory DEFAULT_OBJECT_FACTORY = new DefaultObjectFactory();     private static final ObjectWrapperFactory DEFAULT_OBJECT_WRAPPER_FACTORY = new DefaultObjectWrapperFactory();              public Object intercept(Invocation invocation) throws Throwable {                     StatementHandler statementHandler = (StatementHandler) invocation.getTarget();            MetaObject metaStatementHandler = MetaObject.forObject(statementHandler,            DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY);                      // 分离代理对象链(由于目标类可能被多个拦截器拦截，从而形成多次代理，通过下面的两次循环            // 可以分离出最原始的的目标类)            while (metaStatementHandler.hasGetter("h")) {                Object object = metaStatementHandler.getValue("h");                metaStatementHandler = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY,                 DEFAULT_OBJECT_WRAPPER_FACTORY);            }          // 分离最后一个代理对象的目标类            while (metaStatementHandler.hasGetter("target")) {                Object object = metaStatementHandler.getValue("target");                metaStatementHandler = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY,                 DEFAULT_OBJECT_WRAPPER_FACTORY);            }                    MappedStatement mappedStatement = (MappedStatement)             metaStatementHandler.getValue("delegate.mappedStatement");            // 只重写需要分页的sql语句。通过MappedStatement的ID匹配，默认重写以Page结尾的            //  MappedStatement的sql            BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql");            Object parameterObject = boundSql.getParameterObject();                      if(parameterObject instanceof  PageParam){              if (parameterObject == null) {                  throw new NullPointerException("parameterObject is null!");                } else {                  PageParam page = (PageParam)parameterObject;                    String sql = boundSql.getSql();                    // 重写sql                    String pageSql = buildPageSql(sql, page);                    metaStatementHandler.setValue("delegate.boundSql.sql", pageSql);                    metaStatementHandler.setValue("delegate.rowBounds.offset",                     RowBounds.NO_ROW_OFFSET);                    metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT);                    Connection connection = (Connection) invocation.getArgs()[0];                    // 重设分页参数里的总页数等                    setPageParameter(sql, connection, mappedStatement, boundSql, page);                }          }            // 将执行权交给下一个拦截器            return invocation.proceed();        }            private String buildPageSql(String sql, PageParam page) {           if (page != null) {               StringBuilder pageSql = new StringBuilder();                   pageSql = buildPageSqlForOracle(sql, page);               return pageSql.toString();           } else {             return sql;           }       }            public StringBuilder buildPageSqlForOracle(String sql, PageParam page) {         StringBuilder pageSql = new StringBuilder(100);         String beginrow = String.valueOf((page.getCurrentPage() - 1) * page.getPageSize());           String endrow = String.valueOf(page.getCurrentPage() * page.getPageSize());           pageSql.append("select * from ( select temp.*, rownum row_id from ( ");           pageSql.append(sql);           pageSql.append(" ) temp where rownum <= ").append(endrow);         pageSql.append(") where row_id > ").append(beginrow);         return pageSql;       }            /**      * 从数据库里查询总的记录数并计算总页数，回写进分页参数<code>PageParam</code>,这样调用        * 者就可用通过 分页参数<code>PageParam</code>获得相关信息。      *        * @param sql      * @param connection      * @param mappedStatement      * @param boundSql      * @param page      * @throws SQLException      */       private void setPageParameter(String sql, Connection connection, MappedStatement mappedStatement,               BoundSql boundSql, PageParam page) throws SQLException {           // 记录总记录数           String countSql = "select count(0) from (" + sql + ")";           PreparedStatement countStmt = null;           ResultSet rs = null;           try {               countStmt = connection.prepareStatement(countSql);               BoundSql countBS = new BoundSql(mappedStatement.getConfiguration(), countSql,                       boundSql.getParameterMappings(), boundSql.getParameterObject());               setParameters(countStmt, mappedStatement, countBS, boundSql.getParameterObject());               rs = countStmt.executeQuery();             int totalCount = 0;               if (rs.next()) {                 totalCount = rs.getInt(1);               }             page.setTotalCount(totalCount);               int totalPage = totalCount / page.getPageSize() + ((totalCount % page.getPageSize() == 0) ? 0 : 1);               page.setTotalPage(totalPage);         } catch (SQLException e) {               logger.error("exception", e);         } finally {             try {                   rs.close();               } catch (SQLException e) {                   logger.error("exception", e);               }               try {                   countStmt.close();               } catch (SQLException e) {                   logger.error("exception", e);               }           }       }              private void setParameters(PreparedStatement ps, MappedStatement mappedStatement, BoundSql boundSql,               Object parameterObject) throws SQLException {           ParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, parameterObject, boundSql);           parameterHandler.setParameters(ps);       }            @Override     public Object plugin(Object target) {             if (target instanceof StatementHandler) {               return Plugin.wrap(target, this);         } else {             return target;         }     }          @Override     public void setProperties(Properties arg0) {         } } 将日志的过滤模式调到DEBUG模式，控制台可以打印出SQL 使用上述方法处理的分页查询，其只需要一条SQL语句就可以(Mapper.xml文件的SQL) < select id="selectChannelSettleByParam" parameterType="PageParam" resultMap="RS_CHANNELSETTLE">         <![CDATA[             select  *         ]]>             from channlsettle where 1=1             <if test="params.channelSettleModel.channelId != null and 1000 != params.channelSettleModel.channelId">AND CHANNL_ID=#{params.channelSettleModel.channelId}</if>             <if test="params.channelSettleModel.clearStartTime != null and ‘‘ != params.channelSettleModel.clearStartTime">                 <![CDATA[                          AND to_number(CLEAR_DATE) >= to_number(substr(#{params.channelSettleModel.clearStartTime},0,8))                     ]]>             </if>             <if test="params.channelSettleModel.clearEndTime != null and ‘‘ != params.channelSettleModel.clearEndTime">                 <![CDATA[                          AND to_number(CLEAR_DATE) <= to_number(substr(#{params.channelSettleModel.clearEndTime},0,8))                     ]]>             </if>             order by INSTDATE desc     </select>
控制台打印的SQL: 第一条:select count(0) from (select *  from channlsettle where 1=1 AND CHANNL_ID=? AND to_number(CLEAR_DATE) >= to_number(substr(?,0,8)) AND to_number(CLEAR_DATE) <= to_number(substr(?,0,8)) order by INSTDATE desc)
第二条:select * from ( select temp.*, rownum row_id from ( select *  from channlsettle where 1=1 AND CHANNL_ID=? AND to_number(CLEAR_DATE) >= to_number(substr(?,0,8)) AND to_number(CLEAR_DATE) <= to_number(substr(?,0,8)) order by INSTDATE desc ) temp where rownum <= 20) where row_id > 0
从而让公共类实现了我们需要在Mapper.xml配置文件中重复写入两条SQL的工作，以后没一个分页查询都可以使用。