使用freemarker模板引擎技术批量生成mysql数据库表的POJO实体类

最近琢磨着写个程序自动完成数据库表对应的实体类的代码批量开发，所以想到了freemarker模板引擎技术，生成的实体类（包括表中字段的注释一并生成）开发过程具体步骤如下：

1.首先在项目中pom.xml文件引入freemarker和数据库jdbc依赖

<dependency>
      <groupId>org.freemarker</groupId>
      <artifactId>freemarker</artifactId>
      <version>2.3.16</version>
    </dependency>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.22</version>
</dependency>

2.在项目的类路径resource目录下创建文件夹module，创建模板文件module.ftl。模板文件内容如下：

public class ${myClass.className} {
 
    <#list myClass.fieldList as field>
        //${field.fieldRemarks}
        private ${field.fieldType} ${field.fieldName};
    </#list>
 
    <#list myClass.fieldList as field>
        public ${field.fieldType} get${field.fieldNameUpperFirstLetter}() {
            return ${field.fieldName};
        }
 
        public void set${field.fieldNameUpperFirstLetter}(${field.fieldType} ${field.fieldName}) {
            this.${field.fieldName} = ${field.fieldName};
        }
    </#list>
}

3.创建自定义实体类Field模板文件，内容如下：

//自定义实体类模板
public class Field {
    //字段名
    private String fieldName;
    //字段类型
    private String fieldType;
    //字段注释
    private String fieldRemarks;
    //字段名首字母大写
    private String fieldNameUpperFirstLetter;
 
    public String getFieldName() {
        return fieldName;
    }
 
    public void setFieldName(String fieldName) {
        this.fieldName = fieldName;
    }
 
    public String getFieldType() {
        return fieldType;
    }
 
    public void setFieldType(String fieldType) {
        this.fieldType = fieldType;
    }
 
    public String getFieldRemarks() {
        return fieldRemarks;
    }
 
    public void setFieldRemarks(String fieldRemarks) {
        this.fieldRemarks = fieldRemarks;
    }
 
    public String getFieldNameUpperFirstLetter() {
        return fieldNameUpperFirstLetter;
    }
 
    public void setFieldNameUpperFirstLetter(String fieldNameUpperFirstLetter) {
        this.fieldNameUpperFirstLetter = fieldNameUpperFirstLetter;
    }
}

4.创建生成实体类Field的文件

import java.util.List;
 
public class MyClass {
    //实体类名
    private String className;
    //表字段的集合
    private List<Field> fieldList;
 
    public String getClassName() {
        return className;
    }
 
    public void setClassName(String className) {
        this.className = className;
    }
 
    public List<Field> getFieldList() {
        return fieldList;
    }
 
    public void setFieldList(List<Field> fieldList) {
        this.fieldList = fieldList;
    }
}

5.创建生成实体类的工具类，根据jdbc连接配置，进行数据库操作

import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
 
public class ClassGenerator {
 
    public DatabaseMetaData init(){
        DatabaseMetaData databaseMetaData = null;
        try{
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://192.168.126.133:3306/itrip";
            String user = "root";
            String password = "123456";
            Connection connection = DriverManager.getConnection(url, user, password);
            databaseMetaData = connection.getMetaData();
        }catch (Exception e){
            e.printStackTrace();
        }
        return databaseMetaData;
    }
 
    //根据表名生产出类
    public MyClass generateClass(String tableName){
        MyClass myClass = new MyClass();
        List<Field> fieldList = new ArrayList<Field>();
        DatabaseMetaData databaseMetaData = init();
        try{
            ResultSet rs = databaseMetaData.getColumns(null, "%", tableName, "%");
            while(rs.next()){
                //列名
                String columnName = rs.getString("COLUMN_NAME");
                //类型
                String typeName = rs.getString("TYPE_NAME");
                System.out.println("typeName:" + typeName);
                //注释
                String remarks = rs.getString("REMARKS");
 
                Field field = new Field();
                field.setFieldName(columnName);
                field.setFieldType(columnTypeToFieldType(typeName));
                field.setFieldRemarks(remarks);
                field.setFieldNameUpperFirstLetter(upperFirstLetter(columnName));
                fieldList.add(field);
            }
        }catch (Exception e){
            e.printStackTrace();
        }
 
        myClass.setClassName(tableNameToClassName(tableName));
        myClass.setFieldList(fieldList);
 
        return myClass;
    }
 
    //字段类型转换成属性类型
    public String columnTypeToFieldType(String columnType){
        String fieldType = null;
        switch (columnType) {
            case "INT":
                fieldType = "Integer";
                break;
            case "VARCHAR":
                fieldType = "String";
                break;
            case "CHAR":
                fieldType = "String";
                break;
            case "DATE":
                fieldType = "Date";
                break;
            case "BIGINT":
                fieldType = "Long";
                break;
            default:
                fieldType = "String";
                break;
        }
        return fieldType;
    }
 
    //首字母大写
    public String upperFirstLetter(String src){
        String firstLetter = src.substring(0, 1).toUpperCase();
        String otherLetters = src.substring(1);
        return firstLetter + otherLetters;
    }
 
    //表名转类名
    public String tableNameToClassName(String tableName){
        StringBuilder className = new StringBuilder();
        //aa_bb_cc  AaBbCc
        String[] split = tableName.split("_");
        for (String item : split) {
            className.append(upperFirstLetter(item));
        }
        return className.toString();
    }
}

6.创建生成数据库表对应的POJO实体类文件，指定目录

import cn.code.User;
import freemarker.template.Configuration;
import freemarker.template.Template;
 
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
public class Generator {
 
    public static void main(String[] args) throws Exception{
        //创建Configuration对象
        Configuration configuration = new Configuration();
        //设置模板所在目录
        String path = Generator.class.getClassLoader().getResource("module").getPath();
        configuration.setDirectoryForTemplateLoading(new File(path));
        //获取模板
        Template template = configuration.getTemplate("class.ftl");
        //设置数据并执行
        Map map = new HashMap();
 
        ClassGenerator classGenerator = new ClassGenerator();
        MyClass myClass = classGenerator.generateClass("user");
 
        map.put("myClass", myClass);
 
        Writer writer = new OutputStreamWriter(new FileOutputStream("G:/"+myClass.getClassName()+".java"));
 
        template.process(map, writer);
    }
}

使用freemarker模板引擎技术编写POJO实体类等自定义的类，欢迎下方留言评论，转发+关注！！！

7.支持一下