2021-11-17 分页插件PageHelper使用

在代码中使用分页：PageHelper.startPage方法

// Page类有两个，一个是PageHelper的Page类，另一个是自定义的Page类
public Page<T> queryForPageList(T entity, Page<T> page) {
        com.github.pagehelper.Page<T> pageTemp = PageHelper.startPage(page.getPageNumber(), page.getPageSize(), true);
        this.queryForList(entity);
        page.setTotal(pageTemp.getTotal());
        page.setRows(pageTemp.getResult());
        return page;
    }

public List<T> queryForList(T entity) {
        return this.getSqlSession().selectList(this.obtainNameSpace(entity.getClass()) + ".selectAll", this.buildMap(entity.getClass(), entity));
    }

sql语句的改写，涉及到两个类:OracleParser, MysqlParser
OracleParser类

public class OracleParser extends AbstractParser {
    @Override
    public String getPageSql(String sql) {
        StringBuilder sqlBuilder = new StringBuilder(sql.length() + 120);
        sqlBuilder.append("select * from ( select tmp_page.*, rownum row_id from ( ");
        sqlBuilder.append(sql);
        sqlBuilder.append(" ) tmp_page where rownum <= ? ) where row_id > ?");
        return sqlBuilder.toString();
    }

    @Override
    public Map<String, Object> setPageParameter(MappedStatement ms, Object parameterObject, BoundSql boundSql, Page<?> page) {
        Map<String, Object> paramMap = super.setPageParameter(ms, parameterObject, boundSql, page);
        paramMap.put(PAGEPARAMETER_FIRST, page.getEndRow());
        paramMap.put(PAGEPARAMETER_SECOND, page.getStartRow());
        return paramMap;
    }
}

MysqlParser类

public class MysqlParser extends AbstractParser {
    @Override
    public String getPageSql(String sql) {
        StringBuilder sqlBuilder = new StringBuilder(sql.length() + 14);
        sqlBuilder.append(sql);
        sqlBuilder.append(" limit ?,?");
        return sqlBuilder.toString();
    }

    @Override
    public Map<String, Object> setPageParameter(MappedStatement ms, Object parameterObject, BoundSql boundSql, Page<?> page) {
        Map<String, Object> paramMap = super.setPageParameter(ms, parameterObject, boundSql, page);
        paramMap.put(PAGEPARAMETER_FIRST, page.getStartRow());
        paramMap.put(PAGEPARAMETER_SECOND, page.getPageSize());
        return paramMap;
    }
}