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mybatis3.1分页自动添加总数

2015-12-15 13:49 323 查看

1.mybatis默认分页是内存分页的

类似于下面的DAO签名方法，只要有RowBounds入参，Mybatis即会自动内存分页：

Java代码

@Select("SELECT * FROM cartan_common.t_app s WHERE s.author = #{param.author}")

ArrayList<App> queryList(@Param("param")AppQueryParam appQueryParam,RowBounds rowBounds);

我们必须将其转换为物理分页，也即数据库分页。

2.分页一般都需要自动计算出总行数，而在mybatis中，你必须手动发起两次请求，烦人。

解决思路

1.Mybatis的拦截器是我们动手动脚的地方

Mybatis的架构是非常漂亮的，它允许对多个接口的多个方法定义拦截器（Interceptor）,以下是Mybatis的调用粗线：

我们不但可以对Excutor的方法编写插件，还可以对StatementHandler或ResultSetHandler的方法编写插件。以下是一个Mybatis的插件：

Java代码

getLimitString(originalSql, rowBounds.getOffset(), rowBounds.getLimit())

以下就是使用该方法完成的转换：

引用

SELECT * FROM cartan_common.t_app s WHERE s.author = ?

对应的分页SQL:

SELECT * FROM cartan_common.t_app s WHERE s.author = ? limit ?, ?

3.怎样生成SQL对应的总条数SQL呢？

通过以下的类的MybatisHepler.getCountSql(originalSql)方法即可：

Java代码

package com.ridge.dao.mybatis;

import com.ridge.dao.Paging;

import org.apache.ibatis.session.RowBounds;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class MybatisHepler {

/**

* 获取查询总数对应的SQL

* @param querySelect

* @return

*/

public static String getCountSql(String querySelect) {

querySelect = compress(querySelect);

int orderIndex = getLastOrderInsertPoint(querySelect);

int formIndex = getAfterFormInsertPoint(querySelect);

String select = querySelect.substring(0, formIndex);

//如果SELECT 中包含 DISTINCT 只能在外层包含COUNT

if (select.toLowerCase().indexOf("select distinct") != -1 || querySelect.toLowerCase().indexOf("group by") != -1) {

return new StringBuffer(querySelect.length()).append(

"select count(1) count from (").append(

querySelect.substring(0, orderIndex)).append(" ) t")

.toString();

} else {

return new StringBuffer(querySelect.length()).append(

"select count(1) count ").append(

querySelect.substring(formIndex, orderIndex)).toString();

}

}

/**

* 得到最后一个Order By的插入点位置

*

* @return 返回最后一个Order By插入点的位置

*/

private static int getLastOrderInsertPoint(String querySelect) {

int orderIndex = querySelect.toLowerCase().lastIndexOf("order by");

if (orderIndex == -1) {

orderIndex = querySelect.length();

}else{

if(!isBracketCanPartnership(querySelect.substring(orderIndex, querySelect.length()))){

throw new RuntimeException("My SQL 分页必须要有Order by 语句!");

}

}

return orderIndex;

}

/**

* 将{@code paging}转换为{@link org.apache.ibatis.session.RowBounds}对象

* @param paging

* @return

*/

public static final RowBounds toRowBounds(Paging paging){

return new RowBounds(paging.getRowOffset(),paging.getPageSize());

}

/**

* 得到分页的SQL

*

* @param offset 偏移量

* @param limit 位置

* @return 分页SQL

*/

public static String getPagingSql(String querySelect, int offset, int limit) {

querySelect = compress(querySelect);

String sql = querySelect.replaceAll("[^\\s,]+\\.", "") + " limit " + offset + " ," + limit;

return sql;

}

/**

* 将SQL语句压缩成一条语句，并且每个单词的间隔都是1个空格

* @param sql SQL语句

* @return 如果sql是NULL返回空，否则返回转化后的SQL

*/

private static String compress(String sql) {

return sql.replaceAll("[\r\n]", " ").replaceAll("\\s{2,}", " ");

}

/**

* 得到SQL第一个正确的FROM的的插入点

*/

private static int getAfterFormInsertPoint(String querySelect) {

String regex = "\\s+FROM\\s+";

Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);

Matcher matcher = pattern.matcher(querySelect);

while (matcher.find()) {

int fromStartIndex = matcher.start(0);

String text = querySelect.substring(0, fromStartIndex);

if (isBracketCanPartnership(text)) {

return fromStartIndex;

}

}

return 0;

}

/**

* 判断括号"()"是否匹配,并不会判断排列顺序是否正确

*

* @param text 要判断的文本

* @return 如果匹配返回TRUE, 否则返回FALSE

*/

private static boolean isBracketCanPartnership(String text) {

if (text == null

|| (getIndexOfCount(text, '(') != getIndexOfCount(text, ')'))) {

return false;

}

return true;

}

/**

* 得到一个字符在另一个字符串中出现的次数

*

* @param text 文本

* @param ch 字符

*/

private static int getIndexOfCount(String text, char ch) {

int count = 0;

for (int i = 0; i < text.length(); i++) {

count = (text.charAt(i) == ch) ? count + 1 : count;

}

return count;

}

}

好了，下面给出PaginationInterceptor的完整代码：

Java代码

package com.ridge.dao.mybatis;

import org.apache.commons.lang.reflect.FieldUtils;

import org.apache.commons.logging.Log;

import org.apache.commons.logging.LogFactory;

import org.apache.ibatis.executor.statement.PreparedStatementHandler;

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.ParameterMapping;

import org.apache.ibatis.plugin.*;

import org.apache.ibatis.session.Configuration;

import org.apache.ibatis.session.RowBounds;

import org.hibernate.dialect.Dialect;

import java.sql.Connection;

import java.util.Properties;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

/**

* 默认情况下

* 数据库的类型

*

* @author : chenxh

* @date: 13-7-5

*/

@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class})})

public class PaginationInterceptor implements Interceptor {

private final static Log logger = LogFactory.getLog(PaginationInterceptor.class);

public static final String CONFIGURATION = "configuration";

private static Dialect dialect = null;

private static final String ROW_BOUNDS = "rowBounds";

private static final String BOUND_SQL = "boundSql";

private static final String DIALECT = "dialect";

private static final String SQL = "sql";

private static final String OFFSET = "offset";

private static final String LIMIT = "limit";

public static final String DELEGATE = "delegate";

private static final int CONNECTION_INDEX = 0;

private static final String INTERCEPTOR_CONF = "<plugins>\n" +

"<plugin interceptor=\"" + PaginationInterceptor.class.getCanonicalName() + "\">\n" +

"<property name=\"dialect\" value=\"" + DialetHelper.getSupportDatabaseTypes() + "\"/>\n" +

"</plugin>\n" +

"</plugins>";

@Override

public Object intercept(Invocation invocation) throws Throwable {

RoutingStatementHandler statementHandler = (RoutingStatementHandler) invocation.getTarget();

PreparedStatementHandler preparedStatHandler =

(PreparedStatementHandler) FieldUtils.readField(statementHandler, DELEGATE, true);

final Object[] queryArgs = invocation.getArgs();

Connection connection = (Connection) queryArgs[CONNECTION_INDEX];

RowBounds rowBounds = (RowBounds) FieldUtils.readField(preparedStatHandler, ROW_BOUNDS, true);

BoundSql boundSql = (BoundSql) FieldUtils.readField(preparedStatHandler, BOUND_SQL, true);

Configuration configuration = (Configuration) FieldUtils.readField(preparedStatHandler, CONFIGURATION, true);

//没有分页，直接返回原调用

if (rowBounds == null || rowBounds == RowBounds.DEFAULT) {

return invocation.proceed();

}

//有分页

String originalSql = boundSql.getSql();

//1.获取总行数，将行数绑定到当前线程中

String countSql = MybatisHepler.getCountSql(originalSql);

CountHelper.getCount(countSql, preparedStatHandler, configuration, boundSql, connection);

//2.获取分页的结果集

//////////////////////////////////////////////////////////////////////////////////////////////

String pagingSql = dialect.getLimitString(originalSql, rowBounds.getOffset(), rowBounds.getLimit());

FieldUtils.writeField(boundSql, SQL, pagingSql, true);

int size = 0;

size = getPageParamNum(originalSql, pagingSql);

if (size == 1) {

ParameterMapping.Builder builder = new ParameterMapping.Builder(configuration, LIMIT, Integer.class);

boundSql.getParameterMappings().add(builder.build());

boundSql.setAdditionalParameter(LIMIT, rowBounds.getLimit());

}

if (size == 2) {

ParameterMapping.Builder builder = new ParameterMapping.Builder(

configuration, OFFSET, Integer.class);

boundSql.getParameterMappings().add(builder.build());

boundSql.setAdditionalParameter(OFFSET, rowBounds.getOffset());

builder = new ParameterMapping.Builder(configuration, LIMIT,

Integer.class);

boundSql.getParameterMappings().add(builder.build());

boundSql.setAdditionalParameter(LIMIT, rowBounds.getLimit());

}

FieldUtils.writeField(rowBounds, OFFSET, RowBounds.NO_ROW_OFFSET, true);

FieldUtils.writeField(rowBounds, LIMIT, RowBounds.NO_ROW_LIMIT, true);

if (logger.isDebugEnabled()) {

logger.debug("\n" + originalSql +

"\n对应的分页SQL:\n" +

boundSql.getSql() +

"\n对应的count SQL:\n" +

countSql);

}

return invocation.proceed();

}

/**

* 获取用于控制分页的问号的个数

*

* @param originalSql

* @param pagingSql

* @return

*/

private int getPageParamNum(String originalSql, String pagingSql) {

int size = 0;

String addSql = pagingSql.replace(originalSql, "");

Pattern pattern = Pattern.compile("[?]");

Matcher matcher = pattern.matcher(addSql);

while (matcher.find()) {

size++;

}

return size;

}

@Override

public Object plugin(Object target) {

return Plugin.wrap(target, this);

}

@Override

public void setProperties(Properties properties) {

if (PaginationInterceptor.dialect == null) {

String dialect = properties.getProperty(DIALECT);

if (dialect == null) {

throw new RuntimeException("拦截器未提供dialect的配置，正确配置参见：\n" + INTERCEPTOR_CONF);

}

PaginationInterceptor.dialect = DialetHelper.getDialect(dialect);

}

}

}

如何在保证分页接口签名不变的情况下，将总行数传回去呢？

下面是一个Service层的方法：

Java代码

public Page<App> queryAppList(AppQueryParam queryParam,Paging paging){

List<App> apps = appMapper.queryList(queryParam, MybatisHepler.toRowBounds(paging));

Page<App> appPage = new Page<App>();

appPage.setResult(apps);

appPage.setPageSize(paging.getPageSize());

return appPage;

}

由于DAO appMapper按正常签名只返回一个List，对应的总行数我怎么获取呢？这里我用到了ThreadLocal，因为它让我们可以跨类访问，毕竟Service调用DAO，它们都位于同一个Thread中：

Java代码

package com.ridge.dao.mybatis;

import org.apache.commons.lang.reflect.FieldUtils;

import org.apache.ibatis.executor.statement.PreparedStatementHandler;

import org.apache.ibatis.mapping.BoundSql;

import org.apache.ibatis.mapping.MappedStatement;

import org.apache.ibatis.scripting.defaults.DefaultParameterHandler;

import org.apache.ibatis.session.Configuration;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

/**

* @author : chenxh

* @date: 13-7-8

*/

public class CountHelper {

private static final String MAPPED_STATEMENT = "mappedStatement";

private static Logger logger = LoggerFactory.getLogger(CountHelper.class);

/**

* 保存计算总行数的值

*/

private static ThreadLocal<Integer> totalRowCountHolder = new ThreadLocal<Integer>();

/**

* 获取查询对象的总行数

* @param sql 获取总行数的SQL

* @param statementHandler

* @param configuration

* @param boundSql

* @param connection

* @throws Throwable

*/

static void getCount(String sql, PreparedStatementHandler statementHandler,

Configuration configuration, BoundSql boundSql,

Connection connection)

throws Throwable{

Object parameterObject = statementHandler.getParameterHandler().getParameterObject();

if (logger.isDebugEnabled()) {

logger.debug("Total count SQL [{}] ", sql);

logger.debug("Total count Parameters: {} ", parameterObject);

}

PreparedStatement countStmt = null;

ResultSet rs = null;

try {

countStmt = connection.prepareStatement(sql);

final BoundSql countBS = new BoundSql(configuration, sql,

boundSql.getParameterMappings(), parameterObject);

MappedStatement mappedStatement = (MappedStatement)FieldUtils.readField(statementHandler, MAPPED_STATEMENT, true);

DefaultParameterHandler handler =

new DefaultParameterHandler(mappedStatement, parameterObject, countBS);

handler.setParameters(countStmt);

rs = countStmt.executeQuery();

int count = 0;

if (rs.next()) {

count = rs.getInt(1);

}

if (logger.isDebugEnabled()) {

logger.debug("Total count: {}", count);

}

totalRowCountHolder.set(count);

} finally {

try {

if (rs != null) {

rs.close();

}

} finally {

if (countStmt != null) {

countStmt.close();

}

}

}

}

/**

* 获取当前线程对应的分页查询的总行数

*

* @return

*/

public static int getTotalRowCount() {

return totalRowCountHolder.get();

}

}

这样，以上Service的方法就可以改成：

Java代码

public Page<App> queryAppList(AppQueryParam queryParam,Paging paging){

List<App> apps = appMapper.queryList(queryParam, MybatisHepler.toRowBounds(paging));

Page<App> appPage = new Page<App>();

appPage.setResult(apps);

appPage.setPageSize(paging.getPageSize());

appPage.setTotalRows(CountHelper.getTotalRowCount());//①注意这里！！

return appPage;

}

改进

但是每个Service都要手工调用setTotalRows(CountHelper.getTotalRowCount())是不是有点多余呢？

这里我们可以使用Spring AOP自动做这个事，这样①处的代码就可以不用手工写了。

为些，我写了一个Advice：

Java代码

package com.ridge.dao.mybatis;

import com.ridge.dao.Page;

/**

* @author : chenxh

* @date: 13-7-8

*/

public class TotalRowValueMount {

public void setTotalRows(Page page){

page.setTotalRows(CountHelper.getTotalRowCount());

}

}

在Spring配置文件中，将TotalRowValueMount#setTotalRows(Page page)方法植入到所有返回值类型为Page的方法上，在方法返回时，自动调用setTotalRows(CountHelper.getTotalRowCount());

Xml代码

<aop:config>

<aop:aspect id="pagingQueryAspect" ref="totalRowCounter">

<aop:pointcut id="pagingQueryMethods" expression="execution(public com.ridge.dao.Page *(..))"/>

<aop:after-returning pointcut-ref="pagingQueryMethods" returning="page" method="setTotalRows"/>

</aop:aspect>

</aop:config>

<bean id="totalRowCounter" class="com.ridge.dao.mybatis.TotalRowValueMount"/>

怎么配置mybatis以应用拦截器呢

在mybatis配置文件中，添加拦截器即可：

Xml代码

<?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>

<settings>



<setting name="lazyLoadingEnabled" value="false" />

</settings>

<plugins>

<plugin interceptor="com.ridge.dao.mybatis.PaginationInterceptor">

<property name="dialect" value="MYSQL"/>

</plugin>

</plugins>

<mappers>

<package name="com.xxx.yyy"/>

</mappers>

</configuration>

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