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這篇文章主要講解了“Java 怎么用Velocity引擎生成代碼”，文中的講解內容簡單清晰，易于學習與理解，下面請大家跟著小編的思路慢慢深入，一起來研究和學習“Java 怎么用Velocity引擎生成代碼”吧！
原理
實戰
其原理如圖：
1.配置數據源信息（包括表名）
2.讀取數據表字段信息：列名、類型、字段注釋、表注釋
3.編寫代碼模板，并將該模板加載到內存
4.根據模板所需，組裝Velocity引擎渲染所需字段Map
5.創建Velocity上下文，將代碼模板和替換字段傳入
6.velocity上下文創建引擎，執行merge合并替換并將最終代碼寫入文件
1.通過maven構建項目，引入依賴：
<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目錄下面編寫代碼模板：
VO:
package ${basePackage}.module.${modulePackage}.domain.vo;
import lombok.Data;
#foreach ($dtoImport in $dtoImports)
$dtoImport
#end
import 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
*/
@Data
public 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
*/
@Service
public class ${moduleClass}Service {
@Autowired
private ${moduleClass}Dao ${moduleVar}Dao;
/**
* 根據id查詢
*/
public ${moduleClass}Entity getById(Long id){
return ${moduleVar}Dao.selectById(id);
}
/**
* 分頁查詢
* @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();
}
/**
* 編輯
* @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();
}
/**
* 刪除
* @author ${author}
* @date ${date}
*/
@Transactional(rollbackFor = Exception.class)
public ResponseDTO<String> deleteByIds(List<Long> idList) {
${moduleVar}Dao.deleteByIdList(idList);
return ResponseDTO.succ();
}
/**
* 查詢全部導出對象
* @author ${author}
* @date ${date}
*/
public List<${moduleClass}ExcelVO> queryAllExportData(${moduleClass}QueryDTO queryDTO) {
return ${moduleVar}Dao.queryAllExportData( queryDTO);
}
/**
* 批量查詢導出對象
* @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 id="${moduleClass}VO" type="${basePackage}.module.${modulePackage}.domain.vo.${moduleClass}VO"></resultMap>
<resultMap id="${moduleClass}ExcelVO" type="${basePackage}.module.${modulePackage}.domain.vo.${moduleClass}ExcelVO"></resultMap>
<select id="queryByPage" resultMap="${moduleClass}VO">
select
#foreach($column in $columnList)
#if($velocityCount != $columnList.size())
$column.columnName,
#else
$column.columnName
#end
#end
from ${tableName}
<where>
#foreach($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 id="queryAllExportData" resultMap="${moduleClass}ExcelVO">
select
#foreach($column in $columnList)
#if($velocityCount != $columnList.size())
$column.columnName,
#else
$column.columnName
#end
#end
from ${tableName}
<where>
#foreach($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 id="queryBatchExportData" resultMap="${moduleClass}ExcelVO">
select
#foreach($column in $columnList)
#if($velocityCount != $columnList.size())
$column.columnName,
#else
$column.columnName
#end
#end
from ${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.查詢表信息：
<select id="selectTableDesc" resultType="String">
select
table_comment
from information_schema.tables
where table_schema = (select database()) and table_name = #{tableName}
</select>
<select id="selectTableColumn" resultMap="ColumnDTO">
select
column_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.加載模板、組裝數據
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));
//前端的變量
map.put("ViewUIMessage", "$Message");
map.put("VueRefs", "$refs");5.創建Velocity上下文，生成代碼
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);
}
}
}感謝各位的閱讀，以上就是“Java 怎么用Velocity引擎生成代碼”的內容了，經過本文的學習后，相信大家對Java 怎么用Velocity引擎生成代碼這一問題有了更深刻的體會，具體使用情況還需要大家實踐驗證。這里是億速云，小編將為大家推送更多相關知識點的文章，歡迎關注！
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