一、Mybatis Generator设置分页

Mybatis Generator没有设置分页，但自带了个RowBoundsPlugin分页插件，故而配置

<plugin type="org.mybatis.generator.plugins.RowBoundsPlugin"/>

在mysql数据库进行查询的表分页10条，查很久花费了9s，表的数据也只是十几万行。百思不得其解，查看RowBoundsPlugin生成的代码，如下：

public interface IDomainDao {//省略其他代码@SelectProvider(type=DomainSqlProvider.class, method="selectByExample")@Results({@Result(column="id", property="id", jdbcType=JdbcType.INTEGER, id=true),@Result(column="domain", property="domain", jdbcType=JdbcType.VARCHAR)})List<Domain> selectByExampleWithRowbounds(DomainExample example, RowBounds rowBounds);
}

public class DomainSqlProvider {//省略其他代码public String selectByExample(DomainExample example) {SQL sql = new SQL();if (example != null && example.isDistinct()) {sql.SELECT_DISTINCT("id");} else {sql.SELECT("id");}sql.SELECT("domain");sql.FROM("domain");applyWhere(sql, example, false);if (example != null && example.getOrderByClause() != null) {sql.ORDER_BY(example.getOrderByClause());}return sql.toString();}
}

selectByExample方法里面没有使用limit进行分页，使用mybatis自带的RowBounds功能进行内存分页。故而查询十条数据，其实是把整张表符合要求的数据都查询出来了，在程序的内存进行截取，故而花费了9s。

 

二、解决方案

对Mysql

（1）使用example.setOrderByClause()方法进行sql注入limit分页

（2）重些插件改造example进行分页

public class MySqlLimitPlugin extends PluginAdapter {@Overridepublic boolean validate(List<String> list) {return true;}/*** Example类添加offset和limit属性和set、get方法*/@Overridepublic boolean modelExampleClassGenerated(TopLevelClass topLevelClass, IntrospectedTable introspectedTable) {PrimitiveTypeWrapper integerWrapper = FullyQualifiedJavaType.getIntInstance().getPrimitiveTypeWrapper();Field limit = new Field();limit.setName("limit");limit.setVisibility(JavaVisibility.PRIVATE);limit.setType(integerWrapper);topLevelClass.addField(limit);Method setLimit = new Method();setLimit.setVisibility(JavaVisibility.PUBLIC);setLimit.setName("setLimit");setLimit.addParameter(new Parameter(integerWrapper, "limit"));setLimit.addBodyLine("this.limit = limit;");topLevelClass.addMethod(setLimit);Method getLimit = new Method();getLimit.setVisibility(JavaVisibility.PUBLIC);getLimit.setReturnType(integerWrapper);getLimit.setName("getLimit");getLimit.addBodyLine("return limit;");topLevelClass.addMethod(getLimit);Field offset = new Field();offset.setName("offset");offset.setVisibility(JavaVisibility.PRIVATE);offset.setType(integerWrapper);topLevelClass.addField(offset);Method setOffset = new Method();setOffset.setVisibility(JavaVisibility.PUBLIC);setOffset.setName("setOffset");setOffset.addParameter(new Parameter(integerWrapper, "offset"));setOffset.addBodyLine("this.offset = offset;");topLevelClass.addMethod(setOffset);Method getOffset = new Method();getOffset.setVisibility(JavaVisibility.PUBLIC);getOffset.setReturnType(integerWrapper);getOffset.setName("getOffset");getOffset.addBodyLine("return offset;");topLevelClass.addMethod(getOffset);return true;}/*** Mapper.xml的selectByExampleWithoutBLOBs添加limit*/@Overridepublic boolean sqlMapSelectByExampleWithoutBLOBsElementGenerated(XmlElement element,IntrospectedTable introspectedTable) {addXmlLimit(element);return true;}/*** Mapper.xml的selectByExampleWithBLOBs添加limit*/    @Overridepublic boolean sqlMapSelectByExampleWithBLOBsElementGenerated(XmlElement element,IntrospectedTable introspectedTable) {addXmlLimit(element);return true;}private void addXmlLimit(XmlElement element) {XmlElement ifLimitNotNullElement = new XmlElement("if");ifLimitNotNullElement.addAttribute(new Attribute("test", "limit != null"));XmlElement ifOffsetNotNullElement = new XmlElement("if");ifOffsetNotNullElement.addAttribute(new Attribute("test", "offset != null"));ifOffsetNotNullElement.addElement(new TextElement("limit ${offset}, ${limit}"));ifLimitNotNullElement.addElement(ifOffsetNotNullElement);XmlElement ifOffsetNullElement = new XmlElement("if");ifOffsetNullElement.addAttribute(new Attribute("test", "offset == null"));ifOffsetNullElement.addElement(new TextElement("limit ${limit}"));ifLimitNotNullElement.addElement(ifOffsetNullElement);element.addElement(ifLimitNotNullElement);}/*** 注解selectByExampleWithBLOBs方法生成分页*/public boolean providerSelectByExampleWithBLOBsMethodGenerated(Method method, TopLevelClass topLevelClass, IntrospectedTable introspectedTable) {addAnnotationLimit(method, topLevelClass, introspectedTable);return super.providerSelectByExampleWithBLOBsMethodGenerated(method, topLevelClass, introspectedTable);}/*** 注解selectByExampleWithoutBLOBs方法生成分页*/public boolean providerSelectByExampleWithoutBLOBsMethodGenerated(Method method, TopLevelClass topLevelClass, IntrospectedTable introspectedTable) {addAnnotationLimit(method, topLevelClass, introspectedTable);return super.providerSelectByExampleWithoutBLOBsMethodGenerated(method, topLevelClass, introspectedTable);}private void addAnnotationLimit(Method method, TopLevelClass topLevelClass, IntrospectedTable introspectedTable) {List<String> limits = Arrays.asList("if (example != null && example.getLimit() != null) {","if (example.getOffset() != null) {","sql.OFFSET(example.getOffset());","}","sql.LIMIT(example.getLimit());","}");method.addBodyLines(method.getBodyLines().size() - 1, limits);}}