Download file in csv format for java

最新推荐文章于 2025-06-07 13:21:48 发布

petenover

最新推荐文章于 2025-06-07 13:21:48 发布

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文章标签： Annotation File Download CSV Export Data

本文链接：https://blog.youkuaiyun.com/petenover/article/details/82142895

博客介绍从浏览器下载文件相关工具类，重点讲述注解式实现CSV格式数据导出。提到基于注解导出数据需用反射，要慎重考虑性能问题，实际开发中常用数据频繁下载即便采取缓存等手段也会增加开发过程、效率低，且限制数据源自由。

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上篇轻微的了解了反射,及将要用的工具类,今天咱继续站在巨人的肩膀上学习从浏览器下载文件相关工具类,开发最快的速度,创造更高的成就,就是直接传送门:https://blog.youkuaiyun.com/accountwcx/article/details/46775397;

今天要讲的是第一种实现csv格式数据导出(注解式),闲话少说直接刚;

    private static final String FILE_FORMAT = ".csv";
	private static final String COMMA_DELIMITER = ",";
	private static final String NEW_LINE_SEPARATOR = "\n";
	private static final String ENCODINT_GBK = "gbk";
	private static final String BLANK_STRING = "";
	// 处理下载数据时数字出现科学计数法问题
	private static final String SPECIAL_SYMBOLS = "`";

	/**
	 * 创建csv文件,基于注解实现
	 * @param fileName 文件名
	 * @param list 导出数据对象集合
	 * @return csv文件
	 */
	public File createCsvFile(String fileName, List<T> list) {
		// 注解
		List<Object[]> annotationList = Lists.newArrayList();
		// 标题头
		List<String> headerList = Lists.newArrayList();
		// 域名
		List<String> fieldList = Lists.newArrayList();
		File f = null;
		OutputStreamWriter fileWriter = null;
		try {
			f = File.createTempFile(fileName, FILE_FORMAT);
			fileWriter = new OutputStreamWriter(new FileOutputStream(f), ENCODINT_GBK);
			Class<? extends Object> cla = list.get(0).getClass();
			Field[] fields = cla.getDeclaredFields();
			for (Field field : fields) {
				CsvField csvField = field.getAnnotation(CsvField.class);
				if (Objects.nonNull(csvField)) {
					annotationList.add(new Object[] { csvField, field });
					// 获取域名
					fieldList.add(field.getName());
				}
			}
			// 获取表头
			for (Object[] os : annotationList) {
				String fieldTitle = ((CsvField) os[0]).title();
				// 如果是非必填，加上注释
				int required = ((CsvField) os[0]).required();
				if (required == 0) {
					fieldTitle = fieldTitle + "(非必填)";
				}
				headerList.add(fieldTitle);
			}
			fileWriter.append(listToString(fieldList));
			fileWriter.append(NEW_LINE_SEPARATOR);
			fileWriter.append(listToString(headerList));
			fileWriter.append(NEW_LINE_SEPARATOR);
			//
			for (Object v : list) {
				for (Object[] os : annotationList) {
					CsvField ef = (CsvField) os[0];
					Object val = null;
					// 获取入参值
					try {
						if (StringUtils.isNotBlank(ef.value())) {
							val = ReflectUtils.invokeGetter(v, ef.value());
						} else if (os[1] instanceof Field) {
							val = ReflectUtils.invokeGetter(v, ((Field) os[1]).getName());
						}
					} catch (Exception ex) {
						logger.error("the reflect is error msg is {}", ex);
						// 如果异常,忽略
						val = BLANK_STRING;
					}
					if (ef.isSpecial()) {
						fileWriter.append(SPECIAL_SYMBOLS);
						fileWriter.append(Objects.isNull(val) ? BLANK_STRING : val.toString());
					} else {
						fileWriter.append(Objects.isNull(val) ? BLANK_STRING : val.toString());
					}
					fileWriter.append(COMMA_DELIMITER);
				}
				fileWriter.append(NEW_LINE_SEPARATOR);
			}
			return f;
		} catch (Exception e) {
			logger.error("export data is error,msg is {}", e);
			throw new RuntimeException("export data is error,msg is " + e.getMessage());
		} finally {
			try {
				fileWriter.flush();
				fileWriter.close();
			} catch (IOException e) {
				logger.error("close stream is error,msg is {}", e);
			}

		}

	}

	protected String listToString(List<String> exportName) {
		return Joiner.on(",").join(exportName);
	}

csv注释自定义(可根据自身需求进行导出数据时的限制):

/**
 * csv注解定义
 */
@Target({ ElementType.METHOD, ElementType.FIELD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
public @interface CsvField {
	/**
	 * 导出字段名（默认调用当前字段的“get”方法，如指定导出字段为对象，请填写“对象名.对象属性”，例：“area.name”、“office.
	 * name”）
	 */
	String value() default "";

	/**
	 * 标题
	 */
	String title();

	/**
	 * 必输项(0:非必输；1:必输)
	 */
	int required() default 1;

	/**
	 * 是否加含特殊符号(主要针对导出数据出现科学计数法)
	 */
	boolean isSpecial() default false;
}

测试类:


class Test {
	@CsvField(title = "测试a")
	String a;
	@CsvField(title = "测试b", isSpecial = true)
	Integer b;
	@CsvField(value = "test1.c", title = "测试类Test1")
	Test1 test1;

	public Test1 getTest1() {
		return test1;
	}

	public void setTest1(Test1 test1) {
		this.test1 = test1;
	}

	public String getA() {
		return a;
	}

	public void setA(String a) {
		this.a = a;
	}

	public Integer getB() {
		return b;
	}

	public void setB(Integer b) {
		this.b = b;
	}

	public Test(String a, Integer b) {
		super();
		this.a = a;
		this.b = b;
	}

	public Test(String a, Integer b, Test1 test1) {
		super();
		this.a = a;
		this.b = b;
		this.test1 = test1;
	}

	@Override
	public String toString() {
		return "Test [a=" + a + ", b=" + b + "]";
	}

}

class Test1 {
	@CsvField(title = "测试c")
	String c;

	public String getC() {
		return c;
	}

	public void setC(String c) {
		this.c = c;
	}

	public Test1(String c) {
		super();
		this.c = c;
	}

	@Override
	public String toString() {
		return "Test1 [c=" + c + "]";
	}

}

测试使用:


	public static void main(String[] args) {
		List<Test> list = Lists.newArrayList(new Test("zhang", 1, new Test1("c1")),
				new Test("wang", 2, new Test1("c1")));
		ExportCsvUtils<Test> csvUtils = new ExportCsvUtils<Test>();
		File file = csvUtils.createCsvFile("测试导出", list);
		System.err.println(file);
	}

测试结果(print的是file的文件路径,直接在我的电脑打开就行):

基于注解的方式实现数据导出不可置否的要用到反射,每次用到java反射时都需要慎重考虑是否会影响性能,在实际开发中有些常用数据会频繁被下载,即使加上缓存等一些提高性能手段,也会增加开发过程,效率比较低;同时该方式限制了所需导出数据源的自由(即如果Test1增加属性d被导出,Test也需要增加相应Dto属性d比较繁琐).因此,需要考虑其他可行性方式.