实战Spring boot(二) : PageHelper分页插件使用

版权声明：本文为许晨原创文章，未经本人允许不得转载。 https://blog.csdn.net/Mrxuchen/article/details/82465091

1、引入依赖 pagehlper4.x版本

    <dependency>
                <groupId>com.github.pagehelper</groupId>
                <artifactId>pagehelper</artifactId>
                <version>4.1.0</version>
            </dependency>

2、增加配置文件

@Configuration
            public class MyBatisConfig {
                @Bean
                public PageHelper pageHelper(){
                    PageHelper pageHelper = new PageHelper();
                    Properties p = new Properties();
                    p.setProperty("offsetAsPageNum","true");
                    p.setProperty("rowBoundsWithCount","true");
                    p.setProperty("reasonable","true");
                    pageHelper.setProperties(p);
                    return pageHelper;
                }
            }

3、包装
PageHelper.startPage(page, size);

            PageInfo<VideoOrder> pageInfo = new PageInfo<>(list);

4、基本原理
sqlsessionFactory -> sqlSession-> executor -> mybatis sql statement
通过mybatis plugin 增加拦截器，然后拼装分页
org.apache.ibatis.plugin.Interceptor

5.pagehelper版本升级到5.x

众所周知,插件的小版本更迭都是修修补补,不会做源码上的重构,大版本更迭往往伴随者代码重构,规则修改,例如MySql8.0和5.0版本存在天壤之别,废了一大票第三方连接工具,在pagehelpr5.0版本中,官方用PageInterceptor类代替了PageHelper类

pageHelper是如何在mybatis中工作呢，,解读源码我们可知,是通过mybatis的pulgin实现了Interceptor接口，从而获得要执行的sql语句实现分页技术，而我们的PageHelper5.0.0版本中的这个类，并没有出现implements Interceptor，我们再来看下pagehelper这个包下的其他类，我们发现，有个类很像我们要的，我们进去一看，果然是它：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.github.pagehelper;

import com.github.pagehelper.cache.Cache;
import com.github.pagehelper.cache.CacheFactory;
import com.github.pagehelper.util.MSUtils;
import com.github.pagehelper.util.StringUtil;
import java.lang.reflect.Field;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.executor.Executor;
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.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;

@Intercepts({@Signature(
    type = Executor.class,
    method = "query",
    args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
), @Signature(
    type = Executor.class,
    method = "query",
    args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class}
)})
public class PageInterceptor implements Interceptor {
    protected Cache<String, MappedStatement> msCountMap = null;
    private Dialect dialect;
    private String default_dialect_class = "com.github.pagehelper.PageHelper";
    private Field additionalParametersField;
    private String countSuffix = "_COUNT";

    public PageInterceptor() {
    }

    public Object intercept(Invocation invocation) throws Throwable {
        try {
            Object[] args = invocation.getArgs();
            MappedStatement ms = (MappedStatement)args[0];
            Object parameter = args[1];
            RowBounds rowBounds = (RowBounds)args[2];
            ResultHandler resultHandler = (ResultHandler)args[3];
            Executor executor = (Executor)invocation.getTarget();
            CacheKey cacheKey;
            BoundSql boundSql;
            if (args.length == 4) {
                boundSql = ms.getBoundSql(parameter);
                cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);
            } else {
                cacheKey = (CacheKey)args[4];
                boundSql = (BoundSql)args[5];
            }

            List resultList;
            if (this.dialect.skip(ms, parameter, rowBounds)) {
                resultList = executor.query(ms, parameter, rowBounds, resultHandler, cacheKey, boundSql);
            } else {
                String msId = ms.getId();
                Configuration configuration = ms.getConfiguration();
                Map<String, Object> additionalParameters = (Map)this.additionalParametersField.get(boundSql);
                if (this.dialect.beforeCount(ms, parameter, rowBounds)) {
                    String countMsId = msId + this.countSuffix;
                    MappedStatement countMs = this.getExistedMappedStatement(configuration, countMsId);
                    Long count;
                    if (countMs != null) {
                        count = this.executeManualCount(executor, countMs, parameter, boundSql, resultHandler);
                    } else {
                        countMs = (MappedStatement)this.msCountMap.get(countMsId);
                        if (countMs == null) {
                            countMs = MSUtils.newCountMappedStatement(ms, countMsId);
                            this.msCountMap.put(countMsId, countMs);
                        }

                        count = this.executeAutoCount(executor, countMs, parameter, boundSql, rowBounds, resultHandler);
                    }

                    if (!this.dialect.afterCount(count, parameter, rowBounds)) {
                        Object var24 = this.dialect.afterPage(new ArrayList(), parameter, rowBounds);
                        return var24;
                    }
                }

                if (!this.dialect.beforePage(ms, parameter, rowBounds)) {
                    resultList = executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, cacheKey, boundSql);
                } else {
                    parameter = this.dialect.processParameterObject(ms, parameter, boundSql, cacheKey);
                    String pageSql = this.dialect.getPageSql(ms, boundSql, parameter, rowBounds, cacheKey);
                    BoundSql pageBoundSql = new BoundSql(configuration, pageSql, boundSql.getParameterMappings(), parameter);
                    Iterator var17 = additionalParameters.keySet().iterator();

                    while(true) {
                        if (!var17.hasNext()) {
                            resultList = executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, cacheKey, pageBoundSql);
                            break;
                        }

                        String key = (String)var17.next();
                        pageBoundSql.setAdditionalParameter(key, additionalParameters.get(key));
                    }
                }
            }

            Object var22 = this.dialect.afterPage(resultList, parameter, rowBounds);
            return var22;
        } finally {
            this.dialect.afterAll();
        }
    }

    private Long executeManualCount(Executor executor, MappedStatement countMs, Object parameter, BoundSql boundSql, ResultHandler resultHandler) throws IllegalAccessException, SQLException {
        CacheKey countKey = executor.createCacheKey(countMs, parameter, RowBounds.DEFAULT, boundSql);
        BoundSql countBoundSql = countMs.getBoundSql(parameter);
        Object countResultList = executor.query(countMs, parameter, RowBounds.DEFAULT, resultHandler, countKey, countBoundSql);
        Long count = ((Number)((List)countResultList).get(0)).longValue();
        return count;
    }

    private Long executeAutoCount(Executor executor, MappedStatement countMs, Object parameter, BoundSql boundSql, RowBounds rowBounds, ResultHandler resultHandler) throws IllegalAccessException, SQLException {
        Map<String, Object> additionalParameters = (Map)this.additionalParametersField.get(boundSql);
        CacheKey countKey = executor.createCacheKey(countMs, parameter, RowBounds.DEFAULT, boundSql);
        String countSql = this.dialect.getCountSql(countMs, boundSql, parameter, rowBounds, countKey);
        BoundSql countBoundSql = new BoundSql(countMs.getConfiguration(), countSql, boundSql.getParameterMappings(), parameter);
        Iterator var11 = additionalParameters.keySet().iterator();

        while(var11.hasNext()) {
            String key = (String)var11.next();
            countBoundSql.setAdditionalParameter(key, additionalParameters.get(key));
        }

        Object countResultList = executor.query(countMs, parameter, RowBounds.DEFAULT, resultHandler, countKey, countBoundSql);
        Long count = (Long)((List)countResultList).get(0);
        return count;
    }

    private MappedStatement getExistedMappedStatement(Configuration configuration, String msId) {
        MappedStatement mappedStatement = null;

        try {
            mappedStatement = configuration.getMappedStatement(msId, false);
        } catch (Throwable var5) {
            ;
        }

        return mappedStatement;
    }

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

    public void setProperties(Properties properties) {
        this.msCountMap = CacheFactory.createCache(properties.getProperty("msCountCache"), "ms", properties);
        String dialectClass = properties.getProperty("dialect");
        if (StringUtil.isEmpty(dialectClass)) {
            dialectClass = this.default_dialect_class;
        }

        try {
            Class<?> aClass = Class.forName(dialectClass);
            this.dialect = (Dialect)aClass.newInstance();
        } catch (Exception var6) {
            throw new PageException(var6);
        }

        this.dialect.setProperties(properties);
        String countSuffix = properties.getProperty("countSuffix");
        if (StringUtil.isNotEmpty(countSuffix)) {
            this.countSuffix = countSuffix;
        }

        try {
            this.additionalParametersField = BoundSql.class.getDeclaredField("additionalParameters");
            this.additionalParametersField.setAccessible(true);
        } catch (NoSuchFieldException var5) {
            throw new PageException(var5);
        }
    }
}

综上所述,pagehelper5.0只需要将我们的分页源码改成 PageInterceptor 类型的就好了.

@Configuration
public class MyBatisConfig {
    @Bean
    public PageInterceptor pageHelper() {
        PageInterceptor pageHelper = new PageInterceptor();
        Properties p = new Properties();

        // 设置为true时，会将RowBounds第一个参数offset当成pageNum页码使用
        p.setProperty("offsetAsPageNum", "true");

        //设置为true时，使用RowBounds分页会进行count查询
        p.setProperty("rowBoundsWithCount", "true");
        p.setProperty("reasonable", "true");
        pageHelper.setProperties(p);
        return pageHelper;
    }