使用springboot，整合velocity模板，将数据库中的字典表生成java的枚举代码,
实现controller发送get，然后生成java代码文件并将文件压缩至zip压缩包，前端浏览器访问该地址直接下载zip压缩包

1：引入maven

     <dependency>
            <groupId>org.apache.velocity</groupId>
            <artifactId>velocity-engine-core</artifactId>
            <version>2.3</version>
        </dependency>

2:创建controller

@RestController
@RequestMapping("/gen")
public class GenController {


    @Autowired
    GenService genService;

    @GetMapping("/dict.gen")
    public void batchGenCode(HttpServletResponse response, @RequestParam List<String> req) throws IOException {

        byte[] data = genService.dictGen(req);
        genCode(response, data);
    }



    /**
     * 生成zip文件
     */
    private void genCode(HttpServletResponse response, byte[] data) throws IOException {
        response.reset();
        response.setHeader("Content-Disposition", "attachment; filename=\"code.zip\"");
        response.addHeader("Content-Length", "" + data.length);
        response.setContentType("application/octet-stream; charset=UTF-8");
        IOUtils.write(data, response.getOutputStream());
    }
}

3：逻辑代码

@Component
public class GenService {

    @Resource
    SysDictTypeMapper dictTypeMapper;

    public byte[] dictGen(List<String> req) {
        List<DictRes> dictRes = dictTypeMapper.selectDict(req);

        List<VelocityContext> velocityContexts = new ArrayList<>();
        for (DictRes dictRe : dictRes) {
            VelocityContext velocityContext = new VelocityContext();
            boolean add = true;
            if (velocityContexts.size() > 0 && velocityContexts.stream().anyMatch(v -> v.get("dictId").toString().equals(dictRe.getDictId()))) {
                velocityContext = velocityContexts.stream().filter(v -> v.get("dictId").toString().equals(dictRe.getDictId())).findFirst().get();
                add = false;
            }
            String fileName = toCamelCase(dictRe.getDictType());
            velocityContext.put("fileName", fileName + ".java");
            velocityContext.put("class", fileName);
            velocityContext.put("desc", dictRe.getDictName());
            velocityContext.put("dictId", dictRe.getDictId());

            List<DictRes> dicts = new ArrayList<>();
            if (velocityContext.containsKey("dicts")) {
                dicts = JSON.parseArray(JSON.toJSONString(velocityContext.get("dicts")), DictRes.class);
            }
            dicts.add(dictRe);
            velocityContext.put("dicts", dicts);
            if (add) {
                velocityContexts.add(velocityContext);

            }
        }
        return downloadCode("vm/dict.java.vm", velocityContexts);


    }


    public byte[] downloadCode(String path, List<VelocityContext> velocityContexts) {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        ZipOutputStream zip = new ZipOutputStream(outputStream);
        for (VelocityContext velocityContext : velocityContexts) {
            if (!velocityContext.containsKey("fileName")) {
                throw new RuntimeException("VelocityContext中必须指定fileName");
            }
            generatorCode(path, zip, velocityContext);
        }
        IOUtils.closeQuietly(zip);
        return outputStream.toByteArray();
    }

    private void generatorCode(String path, ZipOutputStream zip, VelocityContext velocityContext) {

        VelocityInitializer.initVelocity();

        // 获取模板文件
        Template template = Velocity.getTemplate(path);

        // 输出渲染后的结果
        StringWriter stringWriter = new StringWriter();
        template.merge(velocityContext, stringWriter);
        // 添加到zip
        try {
            zip.putNextEntry(new ZipEntry(velocityContext.get("fileName").toString()));
            IOUtils.write(stringWriter.toString(), zip, Constants.UTF8);
            IOUtils.closeQuietly(stringWriter);
            zip.flush();
            zip.closeEntry();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }


    }

    /**
     * 下划线
     */
    private static final char SEPARATOR = '_';

    /**
     * 驼峰式命名法
     * 例如：user_name->userName
     */
    public static String toCamelCase(String s) {
        if (s == null) {
            return null;
        }
        s = s.toLowerCase();
        StringBuilder sb = new StringBuilder(s.length());
        boolean upperCase = false;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);

            if (i == 0) {
                sb.append(Character.toUpperCase(c));
                continue;
            }

            if (c == SEPARATOR) {
                upperCase = true;
            } else if (upperCase) {
                sb.append(Character.toUpperCase(c));
                upperCase = false;
            } else {
                sb.append(c);
            }
        }
        return sb.toString();
    }


}

4:用到的实体类

@Data
public class DictRes {

    @ApiModelProperty("主键")
    private String dictId;

    @ApiModelProperty("字典名称")
    private String dictName;

    @ApiModelProperty("字典类型")
    private String dictType;

    @ApiModelProperty("字典枚举名称")
    private String dictLabel;

    @ApiModelProperty("字典枚举代码")
    private String dictValue;
}

5:用到的velocity模板工厂类

public class VelocityInitializer
{
    /**
     * 初始化vm方法
     */
    public static void initVelocity()
    {
        Properties p = new Properties();
        try
        {
            // 加载classpath目录下的vm文件
            p.setProperty("resource.loader.file.class", "org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader");
            // 定义字符集
            p.setProperty(Velocity.INPUT_ENCODING, Constants.UTF8);
            // 初始化Velocity引擎，指定配置Properties
            Velocity.init(p);
        }
        catch (Exception e)
        {
            throw new RuntimeException(e);
        }
    }
}

6: 用到的vm模板文件,需要将文件命名 dict.java.vm 并放到项目的 resource/vm 目录下

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonValue;
import lombok.Getter;
import lombok.Setter;

//${desc}
public enum ${class} {

    #foreach($key in ${dicts})
        ${key.dictValue}("${key.dictValue}", "${key.dictLabel}"),
    #end
        ;

    @JsonValue
    @Getter
    @Setter
    private String code;

    @Getter
    @Setter
    private String info;

    ${class}(String code, String info) {
        this.code = code;
        this.info = info;
    }

    @JsonCreator
    public static ${class} getEnumByValue(String code) {
        for (${class} bt : values()) {
            if (bt.getCode().equals(code)) {
                return bt;
            }
        }
        return null;
    }

    public static String getValue(String info) {
        for (${class} s : ${class}.values()) {
            if (s.getInfo().equals(info)) {
                return s.getCode();
            }
        }
        return "";
    }

    public static String getName(String code) {
        for (${class} s : ${class}.values()) {
            if (s.getCode().equals(code)) return s.getInfo();
        }
        return "";
    }

}