java自动代码生成

article/2025/11/10 6:32:30

1.概述

可在线自动生成代码，省去复制、修改通用模板代码的繁琐过程，减少团队70%以上的开发工作量

基于java的template模板引擎velocity，在定义好模板文件后，动态产生适应业务的java、xml、html、sql等代码文件

2.自动生成过程

首先引入velocity的pom依赖

        <dependency><groupId>commons-io</groupId><artifactId>commons-io</artifactId><version>2.5</version></dependency><dependency><artifactId>velocity</artifactId><groupId>org.apache.velocity</groupId><version>1.7</version></dependency>

其中commons-io为io流的相关框架。

在Resources目录下先定义好模板文件template/User.java.vm

package com.yrr.mvntest;import java.util.Date;
/*** ${comments}*/
@Data
public class ${className} {#foreach ($column in $columns)/*** $column.comments*/#if($column.columnName == $pk.columnName)
@TableId#end
private $column.attrType $column.attrName;
#end
}

通过数据库查出表和列的表备注、列备注、表名、字段名、字段类型等，将其填充入模板，即可生成所需要的代码文件（此处省略查询数据库的过程）：

import java.io.IOException;
import java.io.OutputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import org.apache.commons.io.IOUtils;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;@WebServlet("/MvnServlet")
public class MvnServlet extends HttpServlet {private static final long serialVersionUID = 1L;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {Properties prop = new Properties();prop.put("file.resource.loader.class", "org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader");Velocity.init(prop);//封装模板数据Map<String, Object> map = new HashMap<>();map.put("comments", "表注释");map.put("className", "User");map.put("priName", "id");MvnColumn c1 = new MvnColumn("id","bit","列备注1","id","Integer");MvnColumn c2 = new MvnColumn("name","varchar","列备注2","name","String");MvnColumn c3 = new MvnColumn("mobile","varchar","列备注3","mobile","String");List<MvnColumn> mvnColumns = new ArrayList<>();mvnColumns.add(c1);mvnColumns.add(c2);mvnColumns.add(c3);map.put("columns", mvnColumns);VelocityContext context = new VelocityContext(map);StringWriter sw = new StringWriter();Template tpl = Velocity.getTemplate("template/User.java.vm", "UTF-8");tpl.merge(context, sw);//将数据context合并入模板tpl中，获得的数据写入swOutputStream ouputStream = response.getOutputStream();IOUtils.write(sw.toString(), ouputStream, "UTF-8");IOUtils.closeQuietly(sw);response.setContentType("application/octet-stream;charset=UTF-8");response.setHeader("Content-disposition", "attachment;filename=User.java");}
}

public class MvnColumn {private String columnName;private String dataType;private String comments;private String attrName;private String attrType;public MvnColumn(String columnName, String dataType, String comments, String attrName, String attrType){this.columnName = columnName;this.dataType = dataType;this.comments = comments;this.attrName = attrName;this.attrType = attrType;}public String getColumnName() {return columnName;}public void setColumnName(String columnName) {this.columnName = columnName;}public String getDataType() {return dataType;}public void setDataType(String dataType) {this.dataType = dataType;}public String getComments() {return comments;}public void setComments(String comments) {this.comments = comments;}public String getAttrName() {return attrName;}public void setAttrName(String attrName) {this.attrName = attrName;}public String getAttrType() {return attrType;}public void setAttrType(String attrType) {this.attrType = attrType;}
}

在web客户端即可下载获得User.java代码文件，文件内容如下：

一般情况下，会生成多个代码文件，打包成压缩文件的形式下载：

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import org.apache.commons.io.IOUtils;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;@WebServlet("/MvnServlet")
public class MvnServlet extends HttpServlet {private static final long serialVersionUID = 1L;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {byte[] data = this.generatorCode();response.reset();  response.setHeader("Content-Disposition", "attachment; filename=\"mvntest.zip\"");  response.addHeader("Content-Length", "" + data.length);  response.setContentType("application/octet-stream; charset=UTF-8");  IOUtils.write(data, response.getOutputStream());}public byte[] generatorCode(){ByteArrayOutputStream outputStream = new ByteArrayOutputStream();ZipOutputStream zip = new ZipOutputStream(outputStream);//获取模板列表String[] templates = {"template/User.java.vm"};for (String template : templates) {Properties prop = new Properties();prop.put("file.resource.loader.class", "org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader");Velocity.init(prop);//封装模板数据Map<String, Object> map = new HashMap<>();map.put("comments", "表注释");map.put("className", "User");map.put("priName", "id");MvnColumn c1 = new MvnColumn("id","bit","列备注1","id","Integer");MvnColumn c2 = new MvnColumn("name","varchar","列备注2","name","String");MvnColumn c3 = new MvnColumn("mobile","varchar","列备注3","mobile","String");List<MvnColumn> mvnColumns = new ArrayList<>();mvnColumns.add(c1);mvnColumns.add(c2);mvnColumns.add(c3);map.put("columns", mvnColumns);VelocityContext context = new VelocityContext(map);//渲染模板StringWriter sw = new StringWriter();Template tpl = Velocity.getTemplate(template, "UTF-8");tpl.merge(context, sw);try {//添加到zipzip.putNextEntry(new ZipEntry("main/java/com/yrr/mvntest/User.java"));IOUtils.write(sw.toString(), zip, "UTF-8");IOUtils.closeQuietly(sw);zip.closeEntry();} catch (IOException e) {e.printStackTrace();}}IOUtils.closeQuietly(zip);return outputStream.toByteArray();}
}

在web客户端访问即可获得如下压缩文件：