mybatis框架的两种分页

转载自 https://blog.csdn.net/leozhou13/article/details/50394242

这里我用的是第二种，先记下来，有时间了可以尝试一下最后一种方法

mybatis有两种分页方法

1、内存分页，也就是假分页。本质是查出所有的数据然后根据游标的方式，截取需要的记录。如果数据量大，开销大和内存溢出。

使用方式：

利用自动生成的example类，加入mybatis的RowBounds类,在调用的接口中添加给类的参数

    @Override
    public List<UserVo> selectSelective(UserVo userVo) {

        List<UserVo> listVo = new ArrayList<UserVo>();
        UserPoExample example = new UserPoExample();
        /**
         * 使用mybatis的RowBounds类，该类构造方法中要设置两个int类型参数
         * 第一个是从该条记录开始，第二个是开始后查询的条数
         */
        <strong>RowBounds rowBounds = new RowBounds(0, 5);</strong>
        Criteria criteria = example.createCriteria();
        criteria.andUsernameEqualTo("123");
        criteria.andRoleEqualTo(userVo.getRole());
        example.setOrderByClause("userId desc");//设置排序方式
        example.setStart(10);
        example.setLimit(10);
        UserPo userPo = new UserPo();
        userPo.setUsername("123");
        userPo.setRole(1);
        Page<UserVo> page = new Page<UserVo>();

        List<UserPo> listPo =null;
        try {
            //int countByExample = userPoMapper.countByExample(example);//按照条件查询总数
            //listPo = userPoMapper.selectBySelective(userPo,page);
            listPo = userPoMapper.selectByExample(example,<strong>rowBounds</strong>);

            for(UserPo po:listPo){
                UserVo vo = new UserVo();
                BeanUtils.copyProperties(po, vo);
                listVo.add(vo);
            }
        } catch (Exception e) {
            logger.error(e);
        }

        return listVo;
    }

第二中是，真正的物理分页
在自动生成的example对象中，加入两个成员变量start、和limit

public class UserPoExample {
    private int start;//设置分页开始

    private int limit;//设置分页的每页的数量</strong>

    public int getStart() {
        return start;
    }

    public void setStart(int start) {
        this.start = start;
    }

    public int getLimit() {
        return limit;
    }

    public void setLimit(int limit) {
        this.limit = limit;
    }

最后在对应的xml的方法中添加刚刚加入的条件，直接添加在自动生成的orderByClause后面

 <if test="orderByClause != null" >
   order by ${orderByClause}
 </if>
 <if test="start !=0 or limit!=0">  
   limit #{start},#{limit}
 </if>

通过日志可以看到是真正的分页查询

还有一种是使用分页拦截器实现的

首先在spring-dao的sqlsession工厂里面配置拦截器

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<!-- sqlSessionFactory -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <!-- 数据库连接池 -->
    <property name="dataSource" ref="dataSource" />

    <!-- 批量扫描别名 -->
    <property name="typeAliasesPackage" value="ssm.po" />  

    <!-- spring与mybatis整合不需要mybatis配置文件了,直接扫描mapper下的映射文件 -->
    <property name="mapperLocations" value="classpath:ssm/mapper/*.xml" />

    <!-- MybatisSpringPageInterceptor分页拦截器 -->
    <property name="plugins">  
        <bean class="ssm.utils.MybatisSpringPageInterceptor"></bean>
    </property>

</bean>

拦截器代码：

package ssm.utils;

import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;
import java.util.Properties;

import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.statement.RoutingStatementHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
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.scripting.defaults.DefaultParameterHandler;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Intercepts({ @Signature(method = "prepare", type = StatementHandler.class, args = { Connection.class }),
    @Signature(method = "query", type = Executor.class, args = { MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class }) })
public class MybatisSpringPageInterceptor implements Interceptor {
    private static final Logger log = LoggerFactory.getLogger(MybatisSpringPageInterceptor.class);

    public static final String MYSQL = "mysql";
    public static final String ORACLE = "oracle";

    protected String databaseType;// 数据库类型，不同的数据库有不同的分页方法

    @SuppressWarnings("rawtypes")
    protected ThreadLocal<Page> pageThreadLocal = new ThreadLocal<Page>();

    public String getDatabaseType() {
        return databaseType;
    }

    public void setDatabaseType(String databaseType) {
        if (!databaseType.equalsIgnoreCase(MYSQL) && !databaseType.equalsIgnoreCase(ORACLE)) {
            throw new PageNotSupportException("Page not support for the type of database, database type [" + databaseType + "]");
        }
        this.databaseType = databaseType;
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
        String databaseType = properties.getProperty("databaseType");
        if (databaseType != null) {
            setDatabaseType(databaseType);
        }
    }

    @Override
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public Object intercept(Invocation invocation) throws Throwable {
        if (invocation.getTarget() instanceof StatementHandler) { // 控制SQL和查询总数的地方
            Page page = pageThreadLocal.get();
            if (page == null) { //不是分页查询
                return invocation.proceed();
            }

            RoutingStatementHandler handler = (RoutingStatementHandler) invocation.getTarget();
            StatementHandler delegate = (StatementHandler) ReflectUtil.getFieldValue(handler, "delegate");
            BoundSql boundSql = delegate.getBoundSql();

            Connection connection = (Connection) invocation.getArgs()[0];
            prepareAndCheckDatabaseType(connection); // 准备数据库类型

            if (page.getTotalPage() > -1) {
                if (log.isTraceEnabled()) {
                    log.trace("已经设置了总页数, 不需要再查询总数.");
                }
            } else {
                Object parameterObj = boundSql.getParameterObject();
                MappedStatement mappedStatement = (MappedStatement) ReflectUtil.getFieldValue(delegate, "mappedStatement");
                queryTotalRecord(page, parameterObj, mappedStatement, connection);
            }

            String sql = boundSql.getSql();
            String pageSql = buildPageSql(page, sql);
            if (log.isDebugEnabled()) {
                log.debug("分页时, 生成分页pageSql: " + pageSql);
            }
            ReflectUtil.setFieldValue(boundSql, "sql", pageSql);

            return invocation.proceed();
        } else { // 查询结果的地方
            // 获取是否有分页Page对象
            Page<?> page = findPageObject(invocation.getArgs()[1]);
            if (page == null) {
                if (log.isTraceEnabled()) {
                    log.trace("没有Page对象作为参数, 不是分页查询.");
                }
                return invocation.proceed();
            } else {
                if (log.isTraceEnabled()) {
                    log.trace("检测到分页Page对象, 使用分页查询.");
                }
            }
            //设置真正的parameterObj
            invocation.getArgs()[1] = extractRealParameterObject(invocation.getArgs()[1]);

            pageThreadLocal.set(page);
            try {
                Object resultObj = invocation.proceed(); // Executor.query(..)
                if (resultObj instanceof List) {
                    /* @SuppressWarnings({ "unchecked", "rawtypes" }) */
                    page.setResults((List) resultObj);
                }
                return resultObj;
            } finally {
                pageThreadLocal.remove();
            }
        }
    }

    protected Page<?> findPageObject(Object parameterObj) {
        if (parameterObj instanceof Page<?>) {
            return (Page<?>) parameterObj;
        } else if (parameterObj instanceof Map) {
            for (Object val : ((Map<?, ?>) parameterObj).values()) {
                if (val instanceof Page<?>) {
                    return (Page<?>) val;
                }
            }
        }
        return null;
    }

    /**
     * <pre>
     * 把真正的参数对象解析出来
     * Spring会自动封装对个参数对象为Map<String, Object>对象
     * 对于通过@Param指定key值参数我们不做处理，因为XML文件需要该KEY值
     * 而对于没有@Param指定时，Spring会使用0,1作为主键
     * 对于没有@Param指定名称的参数,一般XML文件会直接对真正的参数对象解析，
     * 此时解析出真正的参数作为根对象
     * </pre>
     * @param parameterObj
     * @return
     */
    protected Object extractRealParameterObject(Object parameterObj) {
        if (parameterObj instanceof Map<?, ?>) {
            Map<?, ?> parameterMap = (Map<?, ?>) parameterObj;
            if (parameterMap.size() == 2) {
                boolean springMapWithNoParamName = true;
                for (Object key : parameterMap.keySet()) {
                    if (!(key instanceof String)) {
                        springMapWithNoParamName = false;
                        break;
                    }
                    String keyStr = (String) key;
                    if (!"0".equals(keyStr) && !"1".equals(keyStr)) {
                        springMapWithNoParamName = false;
                        break;
                    }
                }
                if (springMapWithNoParamName) {
                    for (Object value : parameterMap.values()) {
                        if (!(value instanceof Page<?>)) {
                            return value;
                        }
                    }
                }
            }
        }
        return parameterObj;
    }

    protected void prepareAndCheckDatabaseType(Connection connection) throws SQLException {
        if (databaseType == null) {
            String productName = connection.getMetaData().getDatabaseProductName();
            if (log.isTraceEnabled()) {
                log.trace("Database productName: " + productName);
            }
            productName = productName.toLowerCase();
            if (productName.indexOf(MYSQL) != -1) {
                databaseType = MYSQL;
            } else if (productName.indexOf(ORACLE) != -1) {
                databaseType = ORACLE;
            } else {
                throw new PageNotSupportException("Page not support for the type of database, database product name [" + productName + "]");
            }
            if (log.isInfoEnabled()) {
                log.info("自动检测到的数据库类型为: " + databaseType);
            }
        }
    }

    /**
     * <pre>
     * 生成分页SQL
     * </pre>
     * 
     * @param page
     * @param sql
     * @return
     */
    protected String buildPageSql(Page<?> page, String sql) {
        if (MYSQL.equalsIgnoreCase(databaseType)) {
            return buildMysqlPageSql(page, sql);
        } else if (ORACLE.equalsIgnoreCase(databaseType)) {
            return buildOraclePageSql(page, sql);
        }
        return sql;
    }

    /**
     * <pre>
     * 生成Mysql分页查询SQL
     * </pre>
     * 
     * @param page
     * @param sql
     * @return
     */
    protected String buildMysqlPageSql(Page<?> page, String sql) {
        // 计算第一条记录的位置，Mysql中记录的位置是从0开始的。
        int offset = (page.getPageNo() - 1) * page.getPageSize();
        return new StringBuilder(sql).append(" limit ").append(offset).append(",").append(page.getPageSize()).toString();
    }

    /**
     * <pre>
     * 生成Oracle分页查询SQL
     * </pre>
     * 
     * @param page
     * @param sql
     * @return
     */
    protected String buildOraclePageSql(Page<?> page, String sql) {
        // 计算第一条记录的位置，Oracle分页是通过rownum进行的，而rownum是从1开始的
        int offset = (page.getPageNo() - 1) * page.getPageSize() + 1;
        StringBuilder sb = new StringBuilder(sql);
        sb.insert(0, "select u.*, rownum r from (").append(") u where rownum < ").append(offset + page.getPageSize());
        sb.insert(0, "select * from (").append(") where r >= ").append(offset);
        return sb.toString();
    }

    /**
     * <pre>
     * 查询总数
     * </pre>
     * 
     * @param page
     * @param parameterObject
     * @param mappedStatement
     * @param connection
     * @throws SQLException
     */
    protected void queryTotalRecord(Page<?> page, Object parameterObject, MappedStatement mappedStatement, Connection connection) throws SQLException {
        BoundSql boundSql = mappedStatement.getBoundSql(page);
        String sql = boundSql.getSql();
        String countSql = this.buildCountSql(sql);
        if (log.isDebugEnabled()) {
            log.debug("分页时, 生成countSql: " + countSql);
        }

        List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
        BoundSql countBoundSql = new BoundSql(mappedStatement.getConfiguration(), countSql, parameterMappings, parameterObject);
        ParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, parameterObject, countBoundSql);
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            pstmt = connection.prepareStatement(countSql);
            parameterHandler.setParameters(pstmt);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                long totalRecord = rs.getLong(1);
                page.setTotalRecord(totalRecord);
            }
        } finally {
            if (rs != null)
                try {
                    rs.close();
                } catch (Exception e) {
                    if (log.isWarnEnabled()) {
                        log.warn("关闭ResultSet时异常.", e);
                    }
                }
            if (pstmt != null)
                try {
                    pstmt.close();
                } catch (Exception e) {
                    if (log.isWarnEnabled()) {
                        log.warn("关闭PreparedStatement时异常.", e);
                    }
                }
        }
    }

    /**
     * 根据原Sql语句获取对应的查询总记录数的Sql语句
     * 
     * @param sql
     * @return
     */
    protected String buildCountSql(String sql) {
        int index = sql.indexOf("from");
        return "select count(*) " + sql.substring(index);
    }

    /**
     * 利用反射进行操作的一个工具类
     * 
     */
    private static class ReflectUtil {
        /**
         * 利用反射获取指定对象的指定属性
         * 
         * @param obj 目标对象
         * @param fieldName 目标属性
         * @return 目标属性的值
         */
        public static Object getFieldValue(Object obj, String fieldName) {
            Object result = null;
            Field field = ReflectUtil.getField(obj, fieldName);
            if (field != null) {
                field.setAccessible(true);
                try {
                    result = field.get(obj);
                } catch (IllegalArgumentException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            return result;
        }

        /**
         * 利用反射获取指定对象里面的指定属性
         * 
         * @param obj 目标对象
         * @param fieldName 目标属性
         * @return 目标字段
         */
        private static Field getField(Object obj, String fieldName) {
            Field field = null;
            for (Class<?> clazz = obj.getClass(); clazz != Object.class; clazz = clazz.getSuperclass()) {
                try {
                    field = clazz.getDeclaredField(fieldName);
                    break;
                } catch (NoSuchFieldException e) {
                    // 这里不用做处理，子类没有该字段可能对应的父类有，都没有就返回null。
                }
            }
            return field;
        }

        /**
         * 利用反射设置指定对象的指定属性为指定的值
         * 
         * @param obj 目标对象
         * @param fieldName 目标属性
         * @param fieldValue 目标值
         */
        public static void setFieldValue(Object obj, String fieldName, String fieldValue) {
            Field field = ReflectUtil.getField(obj, fieldName);
            if (field != null) {
                try {
                    field.setAccessible(true);
                    field.set(obj, fieldValue);
                } catch (IllegalArgumentException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }

    public static class PageNotSupportException extends RuntimeException {

        /** serialVersionUID*/
        private static final long serialVersionUID = 1L;

        public PageNotSupportException() {
            super();
        }

        public PageNotSupportException(String message, Throwable cause) {
            super(message, cause);
        }

        public PageNotSupportException(String message) {
            super(message);
        }

        public PageNotSupportException(Throwable cause) {
            super(cause);
        }
    }

}

分页的Page对象

package ssm.utils;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Page<T> {

    public static final int DEFAULT_PAGE_SIZE = 10;

    protected int pageNo = 1; // 当前页, 默认为第1页
    protected int pageSize = DEFAULT_PAGE_SIZE; // 每页记录数
    protected long totalRecord = -1; // 总记录数, 默认为-1, 表示需要查询
    protected int totalPage = -1; // 总页数, 默认为-1, 表示需要计算

    protected List<T> results; // 当前页记录List形式

    public Map<String, Object> params = new HashMap<String, Object>();//设置页面传递的查询参数

    public Map<String, Object> getParams() {
        return params;
    }

    public void setParams(Map<String, Object> params) {
        this.params = params;
    }

    public int getPageNo() {
        return pageNo;
    }

    public void setPageNo(int pageNo) {
        this.pageNo = pageNo;
    }

    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
        computeTotalPage();
    }

    public long getTotalRecord() {
        return totalRecord;
    }

    public int getTotalPage() {
        return totalPage;
    }

    public void setTotalRecord(long totalRecord) {
        this.totalRecord = totalRecord;
        computeTotalPage();
    }

    protected void computeTotalPage() {
        if (getPageSize() > 0 && getTotalRecord() > -1) {
            this.totalPage = (int) (getTotalRecord() % getPageSize() == 0 ? getTotalRecord() / getPageSize() : getTotalRecord() / getPageSize() + 1);
        }
    }

    public List<T> getResults() {
        return results;
    }

    public void setResults(List<T> results) {
        this.results = results;
    }

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder().append("Page [pageNo=").append(pageNo).append(", pageSize=").append(pageSize)
                .append(", totalRecord=").append(totalRecord < 0 ? "null" : totalRecord).append(", totalPage=")
                .append(totalPage < 0 ? "null" : totalPage).append(", curPageObjects=").append(results == null ? "null" : results.size()).append("]");
        return builder.toString();
    }

}

ServiceImpl调用过程：最后查询出来的分页的信息

@Override
    public List<UserVo> selectSelective(UserVo userVo) {

        List<UserVo> listVo = new ArrayList<UserVo>();
//      UserPoExample example = new UserPoExample();
//      Criteria criteria = example.createCriteria();
//      criteria.andUsernameEqualTo(userVo.getUsername());
//      criteria.andRoleEqualTo(userVo.getRole());
//      example.setOrderByClause("userId desc");//设置排序方式
//      example.setStart(0);
//      example.setLimit(10);
        Page<UserVo> page = new Page<UserVo>();

        List<UserPo> listPo =null;
        try {
//          UserPo po1 = new UserPo();
//          po1.setUsername(userVo.getUsername());
//          po1.setRole(userVo.getRole());
            Map<String, Object> params = new HashMap<String, Object>();
            params.put("username", userVo.getUsername());
            params.put("role", userVo.getRole());
            params.put("orderByClause","userId desc");
            page.setParams(params);

            listPo = userPoMapper.selectBySelective(page);

            for(UserPo po:listPo){
                UserVo vo = new UserVo();
                BeanUtils.copyProperties(po, vo);
                listVo.add(vo);
            }
            page.setResults(listVo);
        } catch (Exception e) {
            logger.error(e);
        }

        return listVo;
    }

对应的xml

<select id="selectBySelective" parameterType="ssm.utils.Page" resultType="ssm.po.UserPo">
    select * from tb_user
    <where>
        <if test="params.username != null and params.username !=''">
            userName = #{params.username}
            <!-- userName like '%${usesrname}%' -->
        </if>
        <if test="params.password != null and params.password !=''">
            and password = #{params.password}
        </if>
        <if test="params.sex != null and params.sex !=''">
            and sex = #{params.sex}
        </if>
        <if test="params.age != null and params.age !=''">
            and age = #{params.age}
        </if>
        <if test="params.email != null and params.email !=''">
            and email = #{params.email}
        </if>
        <if test="params.courseid != null and params.courseid !=''">
            and courseId = #{params.courseid}
        </if>
        <if test="params.role != null and params.role !=''">
            and role = #{params.role}
        </if>
        <if test="params.state != null and params.state !=''">
            and state = #{params.state}
        </if>
    </where>
        <if test="params.orderByClause != null and params.orderByClause !=''"></if>
            order by #{params.orderByClause}

  </select>