freemaker根据模板生成Java代码（代码生成器原理）

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freemaker这个jar包可以更加有提前编辑好的模板生成Java代码，做到“不写重复代码”。
实现的步骤如下：
第一步：springboot的pom.xml文件加入依赖包

        <dependency><groupId>org.freemarker</groupId><artifactId>freemarker</artifactId><version>2.3.23</version></dependency>

第二步：编写模板

package ${classPath};public class ${className} {private Integer ${Id};
private String ${userName};
private String ${password};public Integer get${Id}(){
return ${Id};
}public void set${Id}(Integer ${Id}){this.${Id}=${Id};
}public String get${userName}(){
return ${userName};
}public void set${userName}(String ${userName}){
this.${userName}=${userName};}public String get${password}(){
return ${password};
}public void set${password}(String ${password}){
this.${password}=${password};
}}

第三步：编写生成代码的类


import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.HashMap;
import java.util.Map;import freemarker.template.Configuration;
import freemarker.template.Template;public class FreemarkerDemo {private static final String TEMPLATE_PATH = "src/main/java/com/chen/www/chendemo/CodeGenerator";private static final String CLASS_PATH = "src/main/java/com/chen/www/chendemo/CodeGenerator";public static void main(String[] args) {// step1 创建freeMarker配置实例Configuration configuration = new Configuration();Writer out = null;try {// step2 获取模版路径configuration.setDirectoryForTemplateLoading(new File(TEMPLATE_PATH));// step3 创建数据模型Map<String, Object> dataMap = new HashMap<String, Object>();dataMap.put("classPath", "com.chen.www.chendemo");dataMap.put("className", "User");dataMap.put("Id", "Id");dataMap.put("userName", "userName");dataMap.put("password","password");// step4 加载模版文件Template template = configuration.getTemplate("test.ftl");// step5 生成数据File docFile = new File(CLASS_PATH + "\\" + "User.java");out = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(docFile)));// step6 输出文件template.process(dataMap, out);System.out.println("文件创建成功 !");} catch (Exception e) {e.printStackTrace();} finally {try {if (null != out) {out.flush();}} catch (Exception e2) {e2.printStackTrace();}}}}