Java 如何使用Velocity引擎生成代码

其原理如图：

1.配置数据源信息（包括表名）

2.读取数据表字段信息：列名、类型、字段注释、表注释

3.编写代码模板，并将该模板加载到内存

4.根据模板所需，组装Velocity引擎渲染所需字段Map

5.创建Velocity上下文，将代码模板和替换字段传入

6.velocity上下文创建引擎，执行merge合并替换并将最终代码写入文件

1.通过maven构建项目，引入依赖：

<dependency> <artifactId>velocity</artifactId> <groupId>org.apache.velocity</groupId> <exclusions><exclusion> <artifactId>commons-collections</artifactId> <groupId>commons-collections</groupId></exclusion> </exclusions></dependency><dependency> <groupId>org.apache.velocity</groupId> <artifactId>velocity-engine-core</artifactId></dependency>

2.在resources/templates/codegenerator目录下面编写代码模板：

VO:

package ${basePackage}.module.${modulePackage}.domain.vo;import lombok.Data;#foreach ($dtoImport in $dtoImports)$dtoImport#endimport com.fasterxml.jackson.annotation.JsonFormat;import io.swagger.annotations.ApiModelProperty;/** * [ ${tableDesc} ] * * @author ${author} * @version 1.0 * @company ${company} * @copyright (c) ${company}Inc. All rights reserved. * @date ${date} * @since JDK1.8 */@Datapublic class ${moduleClass}VO {#foreach ($column in $columnList)#if($column.fieldType == ’Date’) @ApiModelProperty('${column.columnDesc}') @JsonFormat(pattern = 'yyyy-MM-dd HH:mm:ss', timezone = 'GMT+8') private $column.fieldType $column.fieldName;#else @ApiModelProperty('${column.columnDesc}') private $column.fieldType $column.fieldName;#end#end}

SERVICE:

package ${basePackage}.module.${modulePackage}.service;import com.baomidou.mybatisplus.core.metadata.IPage;import com.baomidou.mybatisplus.extension.plugins.pagination.Page;import ${basePackage}.common.domain.PageResultDTO;import ${basePackage}.common.domain.ResponseDTO;import ${basePackage}.module.${modulePackage}.dao.${moduleClass}Dao;import ${basePackage}.module.${modulePackage}.domain.dto.${moduleClass}AddDTO;import ${basePackage}.module.${modulePackage}.domain.dto.${moduleClass}UpdateDTO;import ${basePackage}.module.${modulePackage}.domain.dto.${moduleClass}QueryDTO;import ${basePackage}.module.${modulePackage}.domain.entity.${moduleClass}Entity;import ${basePackage}.module.${modulePackage}.domain.vo.${moduleClass}VO;import ${basePackage}.module.${modulePackage}.domain.vo.${moduleClass}ExcelVO;import ${basePackage}.util.SmartPageUtil;import ${basePackage}.util.SmartBeanUtil;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import org.springframework.transaction.annotation.Transactional;import java.util.List;/** * [ ${tableDesc} ] * * @author ${author} * @version 1.0 * @company ${company} * @copyright (c) ${company}Inc. All rights reserved. * @date ${date} * @since JDK1.8 */@Servicepublic class ${moduleClass}Service { @Autowired private ${moduleClass}Dao ${moduleVar}Dao; /** * 根据id查询 */ public ${moduleClass}Entity getById(Long id){return ${moduleVar}Dao.selectById(id); } /** * 分页查询 * @author ${author} * @date ${date} */ public ResponseDTO<PageResultDTO<${moduleClass}VO>> queryByPage(${moduleClass}QueryDTO queryDTO) {Page page = SmartPageUtil.convert2QueryPage(queryDTO);IPage<${moduleClass}VO> voList = ${moduleVar}Dao.queryByPage(page, queryDTO);PageResultDTO<${moduleClass}VO> pageResultDTO = SmartPageUtil.convert2PageResult(voList);return ResponseDTO.succData(pageResultDTO); } /** * 添加 * @author ${author} * @date ${date} */ public ResponseDTO<String> add(${moduleClass}AddDTO addDTO) {${moduleClass}Entity entity = SmartBeanUtil.copy(addDTO, ${moduleClass}Entity.class);${moduleVar}Dao.insert(entity);return ResponseDTO.succ(); } /** * 编辑 * @author ${author} * @date ${date} */ @Transactional(rollbackFor = Exception.class) public ResponseDTO<String> update(${moduleClass}UpdateDTO updateDTO) {${moduleClass}Entity entity = SmartBeanUtil.copy(updateDTO, ${moduleClass}Entity.class);${moduleVar}Dao.updateById(entity);return ResponseDTO.succ(); } /** * 删除 * @author ${author} * @date ${date} */ @Transactional(rollbackFor = Exception.class) public ResponseDTO<String> deleteByIds(List<Long> idList) {${moduleVar}Dao.deleteByIdList(idList);return ResponseDTO.succ(); } /** * 查询全部导出对象 * @author ${author} * @date ${date} */ public List<${moduleClass}ExcelVO> queryAllExportData(${moduleClass}QueryDTO queryDTO) {return ${moduleVar}Dao.queryAllExportData( queryDTO); } /** * 批量查询导出对象 * @author ${author} * @date ${date} */ public List<${moduleClass}ExcelVO> queryBatchExportData(List<Long> idList) {return ${moduleVar}Dao.queryBatchExportData(idList); }}

Mapper:

<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE mapper PUBLIC '-//mybatis.org//DTD Mapper 3.0//EN' 'http://mybatis.org/dtd/mybatis-3-mapper.dtd'><mapper namespace='${basePackage}.module.${modulePackage}.dao.${moduleClass}Dao'> <resultMap type='${basePackage}.module.${modulePackage}.domain.vo.${moduleClass}VO'></resultMap> <resultMap type='${basePackage}.module.${modulePackage}.domain.vo.${moduleClass}ExcelVO'></resultMap> <select resultMap='${moduleClass}VO'>select#foreach($column in $columnList)#if($velocityCount != $columnList.size()) $column.columnName,#else $column.columnName#end#endfrom ${tableName}<where>#foreach($queryField in $queryFieldList)#if ($queryField.sqlOperate == ’like’) <if test='queryDTO.${queryField.fieldName} != null and queryDTO.${queryField.fieldName} != ’’'>AND INSTR($queryField.columnName,#{queryDTO.$queryField.fieldName}) </if>#end#if ($queryField.sqlOperate == ’equals’)#if ($queryField.fieldType == ’String’) <if test='queryDTO.${queryField.fieldName} != null and queryDTO.${queryField.fieldName} != ’’'>AND $queryField.columnName = #{queryDTO.$queryField.fieldName} </if>#else <if test='queryDTO.${queryField.fieldName} != null'>AND $queryField.columnName = #{queryDTO.$queryField.fieldName} </if>#end#end#if ($queryField.sqlOperate == ’in’) <if test='queryDTO.${queryField.fieldName}List !=null and queryDTO.${queryField.fieldName}List.size() > 0'>and $queryField.columnName in<foreach collection='queryDTO.${queryField.fieldName}List' open='(' index='index' separator=',' close=')' item='item'> #{item}</foreach> </if>#end#end <if test='queryDTO.createTimeBegin != null '>AND create_time >= #{queryDTO.createTimeBegin} </if> <if test='queryDTO.createTimeEnd != null '>AND create_time <= #{queryDTO.createTimeEnd} </if> <if test='queryDTO.updateTimeBegin != null '>AND update_time >= #{queryDTO.updateTimeBegin} </if> <if test='queryDTO.updateTimeEnd != null '>AND update_time <= #{queryDTO.updateTimeEnd} </if></where> </select> <select resultMap='${moduleClass}ExcelVO'>select#foreach($column in $columnList)#if($velocityCount != $columnList.size()) $column.columnName,#else $column.columnName#end#endfrom ${tableName}<where>#foreach($queryField in $queryFieldList)#if ($queryField.sqlOperate == ’like’) <if test='queryDTO.${queryField.fieldName} != null and queryDTO.${queryField.fieldName} != ’’'>AND INSTR($queryField.columnName,#{queryDTO.$queryField.fieldName}) </if>#end#if ($queryField.sqlOperate == ’equals’)#if ($queryField.fieldType == ’String’) <if test='queryDTO.${queryField.fieldName} != null and queryDTO.${queryField.fieldName} != ’’'>AND $queryField.columnName = #{queryDTO.$queryField.fieldName} </if>#else <if test='queryDTO.${queryField.fieldName} != null'>AND $queryField.columnName = #{queryDTO.$queryField.fieldName} </if>#end#end#if ($queryField.sqlOperate == ’in’) <if test='queryDTO.${queryField.fieldName}List !=null and queryDTO.${queryField.fieldName}List.size() > 0'>and $queryField.columnName in<foreach collection='queryDTO.${queryField.fieldName}List' open='(' index='index' separator=',' close=')' item='item'> #{item}</foreach> </if>#end#end <if test='queryDTO.createTimeBegin != null '>AND create_time >= #{queryDTO.createTimeBegin} </if> <if test='queryDTO.createTimeEnd != null '>AND create_time <= #{queryDTO.createTimeEnd} </if> <if test='queryDTO.updateTimeBegin != null '>AND update_time >= #{queryDTO.updateTimeBegin} </if> <if test='queryDTO.updateTimeEnd != null '>AND update_time <= #{queryDTO.updateTimeEnd} </if></where> </select> <select resultMap='${moduleClass}ExcelVO'>select#foreach($column in $columnList)#if($velocityCount != $columnList.size()) $column.columnName,#else $column.columnName#end#endfrom ${tableName}where id in<foreach collection='idList' open='(' close=')' separator=',' item='item'> #{item}</foreach> </select> <delete id='deleteById'>delete from ${tableName} where id = #{id} </delete> <delete id='deleteByIdList'>delete from ${tableName} where id in<foreach collection='idList' open='(' close=')' separator=',' item='item'> #{item}</foreach> </delete></mapper>

3.查询表信息：

<select resultType='String'> selecttable_comment from information_schema.tables where table_schema = (select database()) and table_name = #{tableName}</select><select resultMap='ColumnDTO'> selectcolumn_name as columnName,data_type as columnType,column_comment as columnDesc from information_schema.columns where table_schema = (select database()) AND table_name = #{tableName} order by ordinal_position</select>

4.加载模板、组装数据

public Map<String, String> codeTemplates(String moduleClass, String basePackage, String modulePackage) { String basePath = basePackage.replaceAll('.', File.separator ); String modulePath = modulePackage.replaceAll('.', File.separator ); String javaPackagePath = 'java' + File.separator + basePath + File.separator + modulePath + File.separator; String xmlPackagePath = 'mapper' + File.separator + modulePath + File.separator; String frontPackagePath = 'web' + File.separator; Map<String, String> templateMap = new HashMap<>(); //后端 templateMap.put('templates/codegenerator/java/Controller.java.vm', javaPackagePath + 'controller' + File.separator + moduleClass + 'Controller.java' ); templateMap.put('templates/codegenerator/java/Dao.java.vm', javaPackagePath + 'dao' + File.separator + moduleClass + 'Dao.java' ); templateMap.put('templates/codegenerator/java/Dao.xml.vm', xmlPackagePath + moduleClass + 'Mapper.xml' ); templateMap.put('templates/codegenerator/java/AddDTO.java.vm', javaPackagePath + 'domain' + File.separator + 'dto' + File.separator + moduleClass + 'AddDTO.java' ); templateMap.put('templates/codegenerator/java/UpdateDTO.java.vm', javaPackagePath + 'domain' + File.separator + 'dto' + File.separator + moduleClass + 'UpdateDTO.java' ); templateMap.put('templates/codegenerator/java/Entity.java.vm', javaPackagePath + 'domain' + File.separator + 'entity' + File.separator + moduleClass + 'Entity.java' ); templateMap.put('templates/codegenerator/java/VO.java.vm', javaPackagePath + 'domain' + File.separator + 'vo' + File.separator + moduleClass + 'VO.java' ); templateMap.put('templates/codegenerator/java/ExcelVO.java.vm', javaPackagePath + 'domain' + File.separator + 'vo' + File.separator + moduleClass + 'ExcelVO.java' ); templateMap.put('templates/codegenerator/java/QueryDTO.java.vm', javaPackagePath + 'domain' + File.separator + 'dto' + File.separator + moduleClass + 'QueryDTO.java' ); templateMap.put('templates/codegenerator/java/Service.java.vm', javaPackagePath + 'service' + File.separator + moduleClass + 'Service.java' ); //前端 String webPackageName = CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, moduleClass).replaceAll('_', '-' ); templateMap.put('templates/codegenerator/web/Api.js.vm', frontPackagePath + 'api' + File.separator + webPackageName + '.js' ); templateMap.put('templates/codegenerator/web/Router.js.vm', frontPackagePath + 'router' + File.separator + webPackageName + '.js' ); templateMap.put('templates/codegenerator/web/List.vue.vm', frontPackagePath + webPackageName + File.separator + webPackageName + '-list.vue' ); templateMap.put('templates/codegenerator/web/ListForm.vue.vm', frontPackagePath + webPackageName + File.separator + 'components' + File.separator + webPackageName + '-list-form.vue' ); return templateMap;}

Properties p = new Properties();p.put('file.resource.loader.class', 'org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader');p.put('directive.foreach.counter.name', 'velocityCount');p.put('directive.foreach.counter.initial.value', '1');Velocity.init(p);Map<String, Object> map = new HashMap<>();map.put('company', codeGenerator.getCompany());map.put('tableName', codeGenerator.getTableName());map.put('basePackage', basePackage);map.put('modulePackage', modulePackage);map.put('moduleClass', moduleClass);map.put('tableDesc', tableDesc);map.put('author', author);map.put('date', date);map.put('moduleVar', moduleVar);map.put('columnList', columnList);map.put('queryFieldList', queryFieldList);map.put('queryImports', queryImports);map.put('dtoImports', dtoImports);map.put('entityImports', entityImports);map.put('webModuleName', CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, moduleClass).replaceAll('_', '-'));map.put('upperCamel', CaseFormat.LOWER_CAMEL.to(CaseFormat.UPPER_CAMEL, moduleClass));//前端的变量map.put('ViewUIMessage', '$Message');map.put('VueRefs', '$refs');

5.创建Velocity上下文，生成代码

VelocityContext context = new VelocityContext(map);private void codeGenerator(VelocityContext context, Map<String, String> codeTemplates) throws Exception { String projectPath = getOutputDir(); Velocity.setProperty('input.encoding', 'UTF-8'); Velocity.setProperty('output.encoding', 'UTF-8'); for (Entry<String, String> entry : codeTemplates.entrySet()) {String template = entry.getKey();String filePath = projectPath + entry.getValue();String fileName = filePath.substring(filePath.lastIndexOf(File.separator) + 1);String fileDir = filePath.replace(fileName, '');File directory = new File(fileDir);if (!directory.exists()) { directory.mkdirs();}FileWriter writer;try { writer = new FileWriter(filePath); Template tpl = Velocity.getTemplate(template, 'UTF-8'); tpl.merge(context, writer); writer.flush(); writer.close();} catch (Exception e) { log.error('', e);} }}

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