mybatis开发一个分页插件、mybatis实现分页、mybatis拦截器

通过官网的mybatis插件说明可知，我们可以通过拦截器进行开发一个插件。

例如这样的：

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        // 开始分页
        MagicPage.startPage(1, 3);
        // 查询
        List<UserEntity> list = mapper.selectAll();
        System.out.println(list);
        // 获取到分页的内容
        PageInfo page = MagicPage.getPage();

        System.out.println(page);

格式就是通过线程变量来实现

MagicPage.start(page,size);
// 执行查询
...
MagicPage.getPage();

先编写一个 MagicPage

import cn.hutool.core.lang.Assert;

/**
 * @author lingkang
 * Created by 2024/3/3
 */
public class MagicPage {
    private static final ThreadLocal<PageInfo> local = new ThreadLocal<>();

    /**
     * 开始分页
     *
     * @param page 默认 1
     * @param size 默认 10
     */
    public static void startPage(int page, int size) {
        Assert.isTrue(page > 0, "page 最小值为 1");
        Assert.isTrue(size > 0, "size 必须大于 0");
        PageInfo info = new PageInfo();
        info.setSize(size);
        info.setPage(page);
        local.set(info);
    }

    public static PageInfo getPage() {
        return local.get();
    }

    public static void removePage() {
        local.remove();
    }
}

PageInfo

@Data
public class PageInfo {
    private int size;
    private int page;
    private long total;
}

mybatis插件实现：

import cn.hutool.core.convert.BasicType;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
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.Signature;

import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Collection;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * 查询分页拦截
 *
 * @author lingkang
 * Created by 2024/3/3
 */
@Intercepts({@Signature(
        type = StatementHandler.class,
        method = "prepare",
        args = {Connection.class, Integer.class})})
public class MagicPageInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        PageInfo page = MagicPage.getPage();
        if (page == null)
            return invocation.proceed();

        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
        BoundSql boundSql = statementHandler.getBoundSql();
        if (!boundSql.getSql().toLowerCase().contains("select")) {
            return invocation.proceed();
        }

        Connection conn = (Connection) invocation.getArgs()[0];
        String totalSql = "select count(*) ";
        TotalConvert convert = pageSql(boundSql.getSql());
        if (convert.getOrderIndex() != 0)
            totalSql += boundSql.getSql().substring(convert.getTotalIndex()) + boundSql.getSql().substring(convert.getOrderIndex());
        else
            totalSql += boundSql.getSql().substring(convert.getTotalIndex());
        PreparedStatement statement = conn.prepareStatement(totalSql);
        Object parameterObject = boundSql.getParameterObject();
        // 设置参数
        if (parameterObject != null) {
            if (parameterObject.getClass().isPrimitive() || BasicType.WRAPPER_PRIMITIVE_MAP.containsKey(parameterObject.getClass())) {
                statement.setObject(1, parameterObject);
            } else if (parameterObject.getClass().isArray()) {
                Object[] arr = (Object[]) parameterObject;
                for (int i = 1; i <= arr.length; i++)
                    statement.setObject(i, arr[i]);
            } else if (parameterObject instanceof Collection) {
                int i = 1;
                for (Object o : (Collection) parameterObject)
                    statement.setObject(i++, o);
            } else if (parameterObject instanceof Map) {
                Map map = (Map) parameterObject;
                int i = 1;
                for (ParameterMapping mapping : boundSql.getParameterMappings())
                    statement.setObject(i++, map.get(mapping.getProperty()));
            } else {
                // 将它当成对象
                int i = 1;
                for (ParameterMapping mapping : boundSql.getParameterMappings()) {
                    Field field = parameterObject.getClass().getDeclaredField(mapping.getProperty());
                    field.setAccessible(true);
                    statement.setObject(i++, field.get(parameterObject));
                }
            }
        }
        ResultSet resultSet = statement.executeQuery();
        if (resultSet.next()) {
            long total = resultSet.getLong(1);
            page.setTotal(total);
            resultSet.close();
        }
        if (page.getTotal() > 0) {
            // 存在分页
            String sql = boundSql.getSql() + " limit " + (page.getPage() - 1) * page.getSize() + "," + page.getSize();
            Field field = BoundSql.class.getDeclaredField("sql");
            field.setAccessible(true);
            field.set(boundSql, sql);
        }
        return invocation.proceed();
    }

    Pattern orderBy = Pattern.compile("order\\s+by");

    /**
     * select id,(select username from user where id=t_order.userid) as username from t_order order by id desc
     */
    private TotalConvert pageSql(String sql) {
        TotalConvert convert = new TotalConvert();
        sql = sql.toLowerCase();
        int index = sql.indexOf("from");
        int start = sql.substring(0, index).indexOf("(");
        while (start != -1) {
            start = sql.indexOf("(", start + 1);
            if (start == -1)
                index = sql.indexOf("from", index + 1);
        }
        convert.setTotalIndex(index);

        // 匹配排序，可能存在排序，需要特殊处理
        Matcher matcher = orderBy.matcher(sql);
        if (matcher.find()) {
            convert.setOrderIndex(matcher.start());
        }
        return convert;
    }
}

需要注意，上面的插件只是做了mysql语法下的分页，如果是sqlserver以及其他数据库需要做调整

配置我们的插件

// 将拦截器添加到配置
configuration.addInterceptor(new MagicPageInterceptor());

执行效果：