Java之利用Freemarker模板引擎实现代码生成器，提高效率

开心一笑

【1.你以为我会眼睁睁的看着你去送死？我会闭着眼睛。2.给你讲个故事，从前有个笨蛋，他非常笨，别人问他问题他只会回答“没有”，这个故事你听过吗？】

视频教程

大家好，我录制的视频《Java之优雅编程之道》已经在CSDN学院发布了，有兴趣的同学可以购买观看，相信大家一定会收获到很多知识的。谢谢大家的支持……

视频地址：http://edu.csdn.net/lecturer/994

提出问题

如何利用 Java + Freemarker 实现代码生成器???

解决问题

* 前言 *

做业务开发的时候，经常要根据建立好的数据库表，生成相关的 Model , DTO , Service, Controller , DAO 等等。包括基本的增删改查。而这些细活往往比较简单且没有挑战性，纯粹苦力活。因此，根据公司的框架，开发一个代码生成器是很有必要的。

这里：
假如你有一定的java基础；
假如你熟悉freemarker模板引擎；
假如你熟悉MVC框架；
假如你熟悉Spring Data 框架

* 技术选型 *

由于代码生成器是要生成很多文件的，包 Test.java , TestDTO.java ,TestController.java , TestServiceImpl.java , ITestService.java , TestDAO.java 等等这些文件。所有考虑用 freemarker 强大的模板引擎，制作相关的模板。

* 实现思路 *

首先，假如在数据库中有一张表 ay_test.

CREATE TABLE "public"."ay_test" (    "id" varchar(32) COLLATE "default" NOT NULL,    "name" varchar(10) COLLATE "default",    "birth_date" timestamp(6),    "remark" text COLLATE "default",    CONSTRAINT "ay_test_pkey" PRIMARY KEY ("id"))

我们首先要获取数据库的连接，这里我只贴出相关的代码。

private final String URL = "jdbc:postgresql://192.168.3.160:10655/cibpm";private final String USER = "postgres";private final String PASSWORD = "888888";private final String DRIVER = "org.postgresql.Driver";public Connection getConnection() throws Exception{    Class.forName(DRIVER);    Connection connection= DriverManager.getConnection(URL, USER, PASSWORD);    return connection;}

获取数据库表的元数据

private final String changeTableName = replaceUnderLineAndUpperCase(tableName);Connection connection = getConnection();DatabaseMetaData databaseMetaData = connection.getMetaData();ResultSet resultSet = databaseMetaData.getColumns(null,"%", tableName,"%");

最后根据元数据获取表字段，注释等等，生成相关的文件

代码实现

Java代码实现

package com.evada.inno.pm.code.generate.util;import com.evada.inno.pm.code.generate.model.ColumnClass;import freemarker.template.Template;import org.apache.commons.lang3.StringUtils;import java.io.*;import java.sql.Connection;import java.sql.DatabaseMetaData;import java.sql.DriverManager;import java.sql.ResultSet;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;/** * 描述：代码生成器 * Created by Ay on 2017/5/1. */public class CodeGenerateUtils {    private final String AUTHOR = "Ay";    private final String CURRENT_DATE = "2017/05/03";    private final String tableName = "tm_project_quality_problem";    private final String packageName = "com.evada.pm.process.manage";    private final String tableAnnotation = "质量问题";    private final String URL = "jdbc:postgresql://192.168.3.160:10655/cibpm";    private final String USER = "postgres";    private final String PASSWORD = "888888";    private final String DRIVER = "org.postgresql.Driver";    private final String diskPath = "D://";    private final String changeTableName = replaceUnderLineAndUpperCase(tableName);    public Connection getConnection() throws Exception{        Class.forName(DRIVER);        Connection connection= DriverManager.getConnection(URL, USER, PASSWORD);        return connection;    }    public static void main(String[] args) throws Exception{        CodeGenerateUtils codeGenerateUtils = new CodeGenerateUtils();        codeGenerateUtils.generate();    }    public void generate() throws Exception{        try {            Connection connection = getConnection();            DatabaseMetaData databaseMetaData = connection.getMetaData();            ResultSet resultSet = databaseMetaData.getColumns(null,"%", tableName,"%");            //生成Mapper文件            generateMapperFile(resultSet);            //生成Dao文件            generateDaoFile(resultSet);            //生成Repository文件            generateRepositoryFile(resultSet);            //生成服务层接口文件            generateServiceInterfaceFile(resultSet);            //生成服务实现层文件            generateServiceImplFile(resultSet);            //生成Controller层文件            generateControllerFile(resultSet);            //生成DTO文件            generateDTOFile(resultSet);            //生成Model文件            generateModelFile(resultSet);        } catch (Exception e) {            throw new RuntimeException(e);        }finally{        }    }    private void generateModelFile(ResultSet resultSet) throws Exception{        final String suffix = ".java";        final String path = diskPath + changeTableName + suffix;        final String templateName = "Model.ftl";        File mapperFile = new File(path);        List<ColumnClass> columnClassList = new ArrayList<>();        ColumnClass columnClass = null;        while(resultSet.next()){            //id字段略过            if(resultSet.getString("COLUMN_NAME").equals("id")) continue;            columnClass = new ColumnClass();            //获取字段名称            columnClass.setColumnName(resultSet.getString("COLUMN_NAME"));            //获取字段类型            columnClass.setColumnType(resultSet.getString("TYPE_NAME"));            //转换字段名称，如 sys_name 变成 SysName            columnClass.setChangeColumnName(replaceUnderLineAndUpperCase(resultSet.getString("COLUMN_NAME")));            //字段在数据库的注释            columnClass.setColumnComment(resultSet.getString("REMARKS"));            columnClassList.add(columnClass);        }        Map<String,Object> dataMap = new HashMap<>();        dataMap.put("model_column",columnClassList);        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateDTOFile(ResultSet resultSet) throws Exception{        final String suffix = "DTO.java";        final String path = "D://" + changeTableName + suffix;        final String templateName = "DTO.ftl";        File mapperFile = new File(path);        Map<String,Object> dataMap = new HashMap<>();        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateControllerFile(ResultSet resultSet) throws Exception{        final String suffix = "Controller.java";        final String path = diskPath + changeTableName + suffix;        final String templateName = "Controller.ftl";        File mapperFile = new File(path);        Map<String,Object> dataMap = new HashMap<>();        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateServiceImplFile(ResultSet resultSet) throws Exception{        final String suffix = "ServiceImpl.java";        final String path = diskPath + changeTableName + suffix;        final String templateName = "ServiceImpl.ftl";        File mapperFile = new File(path);        Map<String,Object> dataMap = new HashMap<>();        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateServiceInterfaceFile(ResultSet resultSet) throws Exception{        final String prefix = "I";        final String suffix = "Service.java";        final String path = diskPath + prefix + changeTableName + suffix;        final String templateName = "ServiceInterface.ftl";        File mapperFile = new File(path);        Map<String,Object> dataMap = new HashMap<>();        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateRepositoryFile(ResultSet resultSet) throws Exception{        final String suffix = "Repository.java";        final String path = diskPath + changeTableName + suffix;        final String templateName = "Repository.ftl";        File mapperFile = new File(path);        Map<String,Object> dataMap = new HashMap<>();        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateDaoFile(ResultSet resultSet) throws Exception{        final String suffix = "DAO.java";        final String path = diskPath + changeTableName + suffix;        final String templateName = "DAO.ftl";        File mapperFile = new File(path);        Map<String,Object> dataMap = new HashMap<>();        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateMapperFile(ResultSet resultSet) throws Exception{        final String suffix = "Mapper.xml";        final String path = diskPath + changeTableName + suffix;        final String templateName = "Mapper.ftl";        File mapperFile = new File(path);        Map<String,Object> dataMap = new HashMap<>();        generateFileByTemplate(templateName,mapperFile,dataMap);    }    private void generateFileByTemplate(final String templateName,File file,Map<String,Object> dataMap) throws Exception{        Template template = FreeMarkerTemplateUtils.getTemplate(templateName);        FileOutputStream fos = new FileOutputStream(file);        dataMap.put("table_name_small",tableName);        dataMap.put("table_name",changeTableName);        dataMap.put("author",AUTHOR);        dataMap.put("date",CURRENT_DATE);        dataMap.put("package_name",packageName);        dataMap.put("table_annotation",tableAnnotation);        Writer out = new BufferedWriter(new OutputStreamWriter(fos, "utf-8"),10240);        template.process(dataMap,out);    }    public String replaceUnderLineAndUpperCase(String str){        StringBuffer sb = new StringBuffer();        sb.append(str);        int count = sb.indexOf("_");        while(count!=0){            int num = sb.indexOf("_",count);            count = num + 1;            if(num != -1){                char ss = sb.charAt(count);                char ia = (char) (ss - 32);                sb.replace(count , count + 1,ia + "");            }        }        String result = sb.toString().replaceAll("_","");        return StringUtils.capitalize(result);    }}

FreeMarkerTemplateUtils工具类

FreeMarkerTemplateUtils工具类用来配置模板所在的路径

package com.evada.inno.pm.code.generate.util;import com.evada.inno.core.exception.BusinessException;import freemarker.cache.ClassTemplateLoader;import freemarker.cache.NullCacheStorage;import freemarker.template.Configuration;import freemarker.template.Template;import freemarker.template.TemplateExceptionHandler;import java.io.IOException;/** * Created by Ay on 2016/7/27. */public class FreeMarkerTemplateUtils {    private FreeMarkerTemplateUtils(){}    private static final Configuration CONFIGURATION = new Configuration(Configuration.VERSION_2_3_22);    static{        //这里比较重要，用来指定加载模板所在的路径        CONFIGURATION.setTemplateLoader(new ClassTemplateLoader(FreeMarkerTemplateUtils.class, "/templates"));        CONFIGURATION.setDefaultEncoding("UTF-8");        CONFIGURATION.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);        CONFIGURATION.setCacheStorage(NullCacheStorage.INSTANCE);    }    public static Template getTemplate(String templateName) throws IOException {        try {            return CONFIGURATION.getTemplate(templateName);        } catch (IOException e) {            throw e;        }    }    public static void clearCache() {        CONFIGURATION.clearTemplateCache();    }}

实体类 ColumnClass

ColumnClass 用来封装 数据库表元数据的信息，如字段名称，字段类型，字段注释等等。

package com.evada.inno.pm.code.generate.model;/** * 数据库字段封装类 * Created by Ay on 2017/5/3. */public class ColumnClass {    /** 数据库字段名称 **/    private String columnName;    /** 数据库字段类型 **/    private String columnType;    /** 数据库字段首字母小写且去掉下划线字符串 **/    private String changeColumnName;    /** 数据库字段注释 **/    private String columnComment;    public String getColumnComment() {        return columnComment;    }    public void setColumnComment(String columnComment) {        this.columnComment = columnComment;    }    public String getColumnName() {        return columnName;    }    public void setColumnName(String columnName) {        this.columnName = columnName;    }    public String getColumnType() {        return columnType;    }    public void setColumnType(String columnType) {        this.columnType = columnType;    }    public String getChangeColumnName() {        return changeColumnName;    }    public void setChangeColumnName(String changeColumnName) {        this.changeColumnName = changeColumnName;    }}

freemarker 模板文件

Freemarker的模板文件，后缀都是以ftl结尾的。

Model.ftl模型模板

Model.ftl可以生成字段的属性，并且可以生成字段属性对应的 set 和 get 方法，包括字段在数据库中对应的注释，以及一些该引入的包和类注释。

package ${package_name}.model;import com.evada.inno.common.domain.BaseModel;import com.evada.inno.common.listener.ICreateListenable;import com.evada.inno.common.listener.IDeleteListenable;import com.evada.inno.common.listener.IModifyListenable;import org.hibernate.annotations.Where;import javax.persistence.*;import java.util.Date;/*** 描述：${table_annotation}模型* @author ${author}* @date ${date}*/@Entity@Table(name="${table_name_small}")@Where(clause = "status > '0'")@Inheritance(strategy= InheritanceType.SINGLE_TABLE)public class ${table_name} extends BaseModel implements ICreateListenable,IModifyListenable,IDeleteListenable {    <#if model_column?exists>        <#list model_column as model>    /**    *${model.columnComment!}    */    <#if (model.columnType = 'varchar' || model.columnType = 'text')>    @Column(name = "${model.columnName}",columnDefinition = "VARCHAR")    private String ${model.changeColumnName?uncap_first};    </#if>    <#if model.columnType = 'timestamp' >    @Column(name = "${model.columnName}",columnDefinition = "TIMESTAMP")    private Date ${model.changeColumnName?uncap_first};    </#if>        </#list>    </#if><#if model_column?exists><#list model_column as model><#if (model.columnType = 'varchar' || model.columnType = 'text')>    public String get${model.changeColumnName}() {        return this.${model.changeColumnName?uncap_first};    }    public void set${model.changeColumnName}(String ${model.changeColumnName?uncap_first}) {        this.${model.changeColumnName?uncap_first} = ${model.changeColumnName?uncap_first};    }</#if><#if model.columnType = 'timestamp' >    public Date get${model.changeColumnName}() {        return this.${model.changeColumnName?uncap_first};    }    public void set${model.changeColumnName}(Date ${model.changeColumnName?uncap_first}) {        this.${model.changeColumnName?uncap_first} = ${model.changeColumnName?uncap_first};    }</#if></#list></#if>}

DTO.ftl模板

DTO.ftl 文件用来生产 DTO 值对象，该对象继承 Model.ftl 文件中的对象。

package ${package_name}.dto;import ${package_name}.model.${table_name};/*** 描述：${table_annotation}DTO* @author ${author}* @date ${date}*/public class ${table_name}DTO extends ${table_name}{}

Service.ftl模板

Service.ftl 模板用来生成服务层实现类，在模板中已经添加了增 ，删，改，查等方法，同时可以注入DAO和repository 到service中，一旦文件生成，就不需要我们去写了，很方便，提高开发的效率。

package ${package_name}.service.impl;import com.evada.inno.core.service.impl.BaseServiceImpl;import ${package_name}.model.${table_name};import ${package_name}.repository.${table_name}Repository;import ${package_name}.service.I${table_name}Service;import ${package_name}.repository.mybatis.${table_name}DAO;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import ${package_name}.dto.${table_name}DTO;import org.apache.commons.beanutils.BeanUtils;import com.evada.inno.core.enums.StatusEnum;/*** 描述：${table_annotation} 服务实现层* @author ${author}* @date ${date}*/@Servicepublic class ${table_name}ServiceImpl extends BaseServiceImpl<${table_name}, String> implements I${table_name}Service {    @Autowired    private ${table_name}DAO ${table_name?uncap_first}DAO;    @Autowired    private ${table_name}Repository ${table_name?uncap_first}Repository;    @Override    public ${table_name}DTO findDTOById(String id) throws Exception {        ${table_name}DTO ${table_name?uncap_first}DTO = ${table_name?uncap_first}DAO.findDTOById(id);        return ${table_name?uncap_first}DTO;    }    @Override    public ${table_name}DTO create${table_name}(${table_name}DTO ${table_name?uncap_first}DTO) throws Exception {        ${table_name} ${table_name?uncap_first} = new ${table_name}();        BeanUtils.copyProperties(${table_name?uncap_first},${table_name?uncap_first}DTO);        ${table_name?uncap_first}.setStatus(StatusEnum.ENABLE.toString());        ${table_name?uncap_first} = ${table_name?uncap_first}Repository.saveAndFlush(${table_name?uncap_first});        return this.findDTOById(${table_name?uncap_first}.getId());    }    @Override    public ${table_name}DTO update${table_name}(${table_name}DTO ${table_name?uncap_first}DTO)throws Exception {        ${table_name} ${table_name?uncap_first} = new ${table_name}();        BeanUtils.copyProperties(${table_name?uncap_first},${table_name?uncap_first}DTO);        ${table_name?uncap_first} = ${table_name?uncap_first}Repository.saveAndFlush(${table_name?uncap_first});        return this.findDTOById(${table_name?uncap_first}.getId());    }

Interface.ftl 模板

Interface.ftl 用来生成服务层接口，接口中定义了增，删，改，查等接口。

package ${package_name}.service;import com.evada.inno.core.service.IBaseService;import ${package_name}.model.${table_name};import ${package_name}.dto.${table_name}DTO;/*** 描述：${table_annotation} 服务实现层接口* @author ${author}* @date ${date}*/public interface I${table_name}Service extends IBaseService<${table_name},String> {    /**    * 描述：根据Id获取DTO    * @param id    */    ${table_name}DTO findDTOById(String id)throws Exception;    ${table_name}DTO create${table_name}(${table_name}DTO ${table_name?uncap_first}DTO) throws Exception;    void delete${table_name}(String id) throws Exception;    ${table_name}DTO update${table_name}(${table_name}DTO ${table_name?uncap_first}DTO) throws Exception;}

Respontory.ftl 模板

Respontory.ftl 用来生成 Repository 文件，这一块是 Spring Data的内容，可能不同的公司，使用的框架不一样。

package ${package_name}.repository;import com.evada.inno.core.repository.BaseJpaRepository;import ${package_name}.model.${table_name};/*** 描述：${table_annotation} Repository接口* @author ${author}* @date ${date}*/public interface ${table_name}Repository extends BaseJpaRepository<${table_name}, String> {}

Mappter.ftl 模板

Mappter.ftl 用来生成 MyBatis 使用到的 mappter 文件，在文件中，定义了查询的sql语句。

<?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="${package_name}.repository.mybatis.${table_name}DAO">    <resultMap id="${table_name}DTOResultMap" type="${package_name}.dto.${table_name}DTO"></resultMap>    <sql id="findDtoSql">        select * from (        select * from  ${table_name_small} temp        ) t    </sql>    <select id="findDTOById" parameterType="String" resultMap="${table_name}DTOResultMap">        <include refid="findDtoSql"></include>        <where>            and t.id = ${r'#{id}'}        </where>    </select>    <select id="find${table_name}Page" parameterType="${package_name}.dto.${table_name}DTO" resultMap="${table_name}DTOResultMap">        <include refid="findDtoSql" />        <where>        </where>    </select></mapper>

Controller.ftl 模板

Controller.ftl 文件用来生成控制层类，类中已经帮我们生成了，增，删，改，查等路由。同时可以注入接口道控制层中。

package ${package_name}.controller;import com.evada.inno.core.annotation.Rest;import ${package_name}.service.I${table_name}Service;import ${package_name}.model.${table_name};import ${package_name}.dto.${table_name}DTO;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.PathVariable;import org.springframework.web.bind.annotation.RequestBody;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestMethod;import org.springframework.http.MediaType;import com.evada.inno.common.domain.ResultData;import com.evada.inno.core.util.AssertUtils;/*** 描述：${table_annotation}控制层* @author ${author}* @date ${date}*/@Rest(${table_name}.class)public class ${table_name}Controller {    @Autowired    private I${table_name}Service ${table_name?uncap_first}Service;    /**    * 描述：根据Id 查询    * @param id  ${table_annotation}id    */    @RequestMapping(value = "/{id}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)    public ResultData findById(@PathVariable("id") String id)throws Exception {        ${table_name}DTO ${table_name?uncap_first}DTO = ${table_name?uncap_first}Service.findDTOById(id);        AssertUtils.checkResourceFound(${table_name?uncap_first}DTO);        return new ResultData(${table_name}DTO.class, ${table_name?uncap_first}DTO);    }    /**    * 描述:创建${table_annotation}    * @param ${table_name?uncap_first}DTO  ${table_annotation}DTO    */    @RequestMapping(value = "", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)    public ResultData create(@RequestBody ${table_name}DTO ${table_name?uncap_first}DTO) throws Exception {        return new ResultData(${table_name}.class,${table_name?uncap_first}Service.create${table_name}(${table_name?uncap_first}DTO));    }    /**    * 描述：删除${table_annotation}    * @param id ${table_annotation}id    */    @RequestMapping(value = "/{id}/bulk", method = RequestMethod.DELETE, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)    public void deleteById(@PathVariable("id") String id) throws Exception {        ${table_name?uncap_first}Service.deleteById(id);    }    /**    * 描述：更新${table_annotation}    * @param id ${table_annotation}id    */    @RequestMapping(value = "/{id}", method = RequestMethod.PUT, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)    public ResultData update${table_name}(@PathVariable("id") String id,@RequestBody ${table_name}DTO ${table_name?uncap_first}DTO) throws Exception {        ${table_name?uncap_first}DTO.setId(id);        return new ResultData(${table_name}.class,${table_name?uncap_first}Service.update${table_name}(${table_name?uncap_first}DTO));    }}

通过上面的代码生成，我们就可以把生成的文件复制到相关的目录，重新启动系统，这样，基本的增，删，改，查就实现了。

读书感悟

来自东野圭吾《信》

• “大多数人都想置身于远离罪犯的地方。和犯罪者，特别是犯下抢劫杀人这样恶心犯罪的人，哪怕是间接的关系也不想有。因为稍微有点什么关系，没准也会被卷入莫名其妙的事情中去。排斥犯罪者或是与其近似的人，是非常正当的行为，也可以说是正当防卫的本能。”
• 犯罪者必须要有这样的思想准备，就是自己犯罪的同时也抹杀了自己亲属在社会上的存在。
• 所谓偏见，就是不平等看待，其产生的根源就在于人的自私本性。这里的不平等看待，其实可以视为一种处理各种社会关系时的态度平衡缺失，而总是向有利于自己的一方倾斜，除非不同的立场之间不存在厉害冲突。一般情况下，人都是首先从自己的角度来看问题，而不会力图站在他人的立场来考量，完全意义上的中立是不可能的，由己及人是必然的思维定势，偏见遂自然而生。

经典故事

　
【一只小青蛙厌倦了常年生活的小水沟——水沟的水越来越少，它已经没有什么食物了。小青蛙每天都不停地蹦，想要逃离这个地方。而它的同伴整日懒洋洋地蹲在浑浊的水洼里，说：“现在不是还饿不死
吗?你着什么急?”终于有一天，小青蛙纵身一跃，跳进了旁边的一个大河塘，那里面有很多好吃的，它可以自由游弋。小青蛙呱呱地呼唤自己的伙伴：“你快过来吧，这边简直是天堂!”但是它的同伴说：“我在这里已经习惯了，我从小就生活在这里，懒得动了!” 不久，水沟里的水干了，小青蛙的同伴活活饿死了。】

大神文章

【1】Freemarker官网
【2】可用于企业级开发的JAVA代码生成器
【3】 一个java代码生成器的简单实现

其他

如果有带给你一丝丝小快乐，就让快乐继续传递下去，欢迎点赞、顶、欢迎留下宝贵的意见、多谢支持！