一、Mybatis Generator設置分頁

Mybatis Generator沒有設置分頁，但自帶了個RowBoundsPlugin分頁插件，故而配置

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

在mysql數據庫進行查詢的表分頁10條，查很久花費了9s，表的數據也只是十幾萬行。百思不得其解，查看RowBoundsPlugin生成的代碼，如下：

public interface IDomainDao {//省略其他代碼@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 {//省略其他代碼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方法里面沒有使用limit進行分頁，使用mybatis自帶的RowBounds功能進行內存分頁。故而查詢十條數據，其實是把整張表符合要求的數據都查詢出來了，在程序的內存進行截取，故而花費了9s。

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二、解決方案

對Mysql

（1）使用example.setOrderByClause()方法進行sql注入limit分頁

（2）重些插件改造example進行分頁

public class MySqlLimitPlugin extends PluginAdapter {@Overridepublic boolean validate(List<String> list) {return true;}/*** Example類添加offset和limit屬性和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方法生成分頁*/public boolean providerSelectByExampleWithBLOBsMethodGenerated(Method method, TopLevelClass topLevelClass, IntrospectedTable introspectedTable) {addAnnotationLimit(method, topLevelClass, introspectedTable);return super.providerSelectByExampleWithBLOBsMethodGenerated(method, topLevelClass, introspectedTable);}/*** 注解selectByExampleWithoutBLOBs方法生成分頁*/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);}}

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