1. Page

package com.sm.model;

import java.util.List;

public class Page<T> {

    public static final int DEFAULT_PAGE_SIZE = 20;

    protected int pageNo = 1; // 當前頁, 默覺得第1頁
    protected int pageSize = DEFAULT_PAGE_SIZE; // 每頁記錄數
    protected long totalRecord = -1; // 總記錄數, 默覺得-1, 表示須要查詢
 

    protected int totalPage = -1; // 總頁數, 默覺得-1, 表示須要計算

    protected List<T> results; // 當前頁記錄List形式


    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(", results=").append(results == null ?
 "null" : results).append("]");
        return builder.toString();
    }

}

2. 實現攔截器

package com.sm.model;

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.DefaultParameterHandler;
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.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 PageInterceptor implements Interceptor {

    private static final Logger log = LoggerFactory.getLogger(PageInterceptor.class);

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

    protected String databaseType;// 數據庫類型。不同的數據庫有不同的分頁方法

    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和查詢總數的地方
            Page page = pageThreadLocal.get();
            if (page == null) { //不是分頁查詢
                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); // 準備數據庫類型

            if (page.getTotalPage() > -1) {
                if (log.isTraceEnabled()) {
                    log.trace("已經設置了總頁數, 不須要再查詢總數.");
                }
            } 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("分頁時, 生成分頁pageSql: " + pageSql);
            }
            ReflectUtil.setFieldValue(boundSql, "sql", pageSql);

            return invocation.proceed();
        } else { // 查詢結果的地方
            // 獲取是否有分頁Page對象
            Page<?> page = findPageObject(invocation.getArgs()[1]);
            if (page == null) {
                if (log.isTraceEnabled()) {
                    log.trace("沒有Page對象作為參數, 不是分頁查詢.");
                }
                return invocation.proceed();
            } else {
                if (log.isTraceEnabled()) {
                    log.trace("檢測到分頁Page對象, 使用分頁查詢.");
                }
            }
            //設置真正的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>
     * 把真正的參數對象解析出來
     * Spring會自己主動封裝對個參數對象為Map<String, Object>對象
     * [email protected]，由於XML文件須要該KEY值
     * [email protected]，Spring會使用0,1作為主鍵
     * [email protected],一般XML文件會直接對真正的參數對象解析。
     * 此時解析出真正的參數作為根對象
     * </pre>
     * @author jundong.xu_C
     * @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("自己主動檢測到的數據庫類型為: " + databaseType);
            }
        }
    }

    /**
     * <pre>
     * 生成分頁SQL
     * </pre>
     * 
     * @author jundong.xu_C
     * @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分頁查詢SQL
     * </pre>
     * 
     * @author jundong.xu_C
     * @param page
     * @param sql
     * @return
     */
    protected String buildMysqlPageSql(Page<?> page, String sql) {
        // 計算第一條記錄的位置，Mysql中記錄的位置是從0開始的。
        int offset = (page.getPageNo() - 1) * page.getPageSize();
        return new StringBuilder(sql).append(" limit ").append(offset).append(",").append(page.getPageSize()).toString();
    }

    /**
     * <pre>
     * 生成Oracle分頁查詢SQL
     * </pre>
     * 
     * @author jundong.xu_C
     * @param page
     * @param sql
     * @return
     */
    protected String buildOraclePageSql(Page<?> page, String sql) {
        // 計算第一條記錄的位置。Oracle分頁是通過rownum進行的。而rownum是從1開始的
        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>
     * 查詢總數
     * </pre>
     * 
     * @author jundong.xu_C
     * @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("分頁時, 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("關閉ResultSet時異常.", e);
                    }
                }
            if (pstmt != null)
                try {
                    pstmt.close();
                } catch (Exception e) {
                    if (log.isWarnEnabled()) {
                        log.warn("關閉PreparedStatement時異常.", e);
                    }
                }
        }
    }

    /**
     * 依據原Sql語句獲取相應的查詢總記錄數的Sql語句
     * 
     * @param sql
     * @return
     */
    protected String buildCountSql(String sql) {
        int index = sql.indexOf("from");
        return "select count(*) " + sql.substring(index);
    }

    /**
     * 利用反射進行操作的一個工具類
     * 
     */
    private static class ReflectUtil {
        /**
         * 利用反射獲取指定對象的指定屬性
         * 
         * @param obj 目標對象
         * @param fieldName 目標屬性
         * @return 目標屬性的值
         */
        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;
        }

        /**
         * 利用反射獲取指定對象裏面的指定屬性
         * 
         * @param obj 目標對象
         * @param fieldName 目標屬性
         * @return 目標字段
         */
        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) {
                    // 榪欓噷涓嶇敤鍋氬鐞嗭紝瀛愮被娌℃湁璇ュ瓧孌靛彲鑳藉搴旂殑鐖剁被鏈夛紝閮芥病鏈夊氨榪斿洖null銆?
                }
            }
            return field;
        }

        /**
         * 利用反射設置指定對象的指定屬性為指定的值
         * 
         * @param obj 目標對象
         * @param fieldName 目標屬性
         * @param fieldValue 目標值
         */
        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 {

        public PageNotSupportException() {
            super();
        }

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

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

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

}

3. spring配置文件（mybatis已和spring整合）

    <!-- 配置mybatis的sqlSessionFactory -->
    <bean id="sqlSessionFactoryBean" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        <!-- 配置了typeAliasesPackage之後，在映射文件裏，這個包下的實體類能夠不寫全名 -->
        <property name="typeAliasesPackage" value="com.sm.model"></property>
        <!-- 配置映射映射文件的位置 -->
        <property name="mapperLocations" value="classpath:resources/mapper/*.xml"></property>
        <property name="plugins">
            <!-- 分頁攔截器 -->
            <bean class="com.sm.model.PageInterceptor"></bean>
        </property>
    </bean>

4. mapper.xml

<select id="getUsers" resultType="User" parameterType="Map">
    select * from user where username=#{user.username}
</select>

6. DAO

List<User> getUsers(Map map);

7. 測試

Page page = new Page();
//配置分頁參數
page.setPageNo(1);
page.setPageSize(3);
//條件查詢，傳參
User user = new User();
user.setUsername("2");

Map map = new HashMap<>();
map.put("user", user);
map.put("page", page);

List<User> list = userDAO.getUsers(map);
System.out.println(list);
System.out.println(page);

8. 總結

上面的分頁攔截器，拷下來直接用就好了。假設想了解實現原理。能夠看慕課網的視頻通過自己主動回復機器人學Mybatis—加強版

myBatis學習筆記（10）——使用攔截器實現分頁查詢