Java中一些文件操作常用转换
工作中偶尔遇到一些操作文件时，需要转换文件格式的情况，以下为一些常用操作：
1、上传文件时将图片转pdf再上传
@SneakyThrows
public static void main(String[] args) {
File file = new File("C:\\Users\\Administrator\\Downloads\\1.jpg");
FileInputStream fileInputStream;
MultipartFile multipartFile = null;
try {
fileInputStream = new FileInputStream(file);
multipartFile = new MockMultipartFile(file.getName(),file.getName(),
ContentType.APPLICATION_OCTET_STREAM.toString(),fileInputStream);
} catch (Exception e) {
log.error("file转MultipartFile失败", e);
}
MultipartFile[] multipartFiles = {multipartFile};
byte[] bytes = getPdfBytes(multipartFiles);
System.out.println(Base64.getEncoder().encodeToString(bytes));
InputStream inputStream = new ByteArrayInputStream(bytes);
MultipartFile mfile = new MockMultipartFile(ContentType.APPLICATION_OCTET_STREAM.toString(), inputStream);
//...以下为上传部分
}
@SneakyThrows
public static byte[] getPdfBytes(MultipartFile[] imagesFiles) {
PDDocument document = new PDDocument();
for (MultipartFile datum : imagesFiles) {
String filename = datum.getOriginalFilename();
String fileSuffix = filename.substring(filename.lastIndexOf(".") + 1);
Iterator readers = ImageIO.getImageReadersByFormatName(fileSuffix);
ImageReader reader = (ImageReader) readers.next();
ImageInputStream input = ImageIO.createImageInputStream(datum.getInputStream());
reader.setInput(input, true);
int width = reader.getWidth(0);
int height = reader.getHeight(0);
PDPage pdPage = new PDPage(new PDRectangle(width, height));
document.addPage(pdPage);
PDImageXObject pdImageXObject = PDImageXObject.createFromByteArray(document, datum.getBytes(), "图片转pdf失败");
PDPageContentStream contentStream = new PDPageContentStream(document, pdPage);
//写入图片
contentStream.drawImage(pdImageXObject, 0, 0);
contentStream.close();
}
ByteArrayOutputStream output = new ByteArrayOutputStream();
document.save(output);
document.close();
return output.toByteArray();
}
2、将pdf转换成jpg
@SneakyThrows
public static void main(String[] args) {
String filePath = "C:\\Users\\Administrator\\Downloads\\202xxxxx税票.pdf"; // 替换为你的文件路径
byte[] fileContent = Files.readAllBytes(Paths.get(filePath));
String base64 = Base64.getEncoder().encodeToString(fileContent);
String jpg_base64 = base64pdftojpg(base64);
System.out.println(jpg_base64);
}
方法传入base64的pdf文件得到base64类型的jpg
private static String base64pdftojpg(String base64) {
String jpg_base64 = null;
Base64Decoder decoder = new Base64Decoder();
try {
// Base64解码
byte[] pdf_bytes = decoder.decode(base64);
PDDocument doc = PDDocument.load(pdf_bytes);
int size = doc.getNumberOfPages();
/*图像合并使用的参数*/
//定义宽度
int width = 0;
// 保存一张图片中的RGB数据
int[] singleImgRGB;
// 定义高度，后面用于叠加
int shiftHeight = 0;
//保存每张图片的像素值
BufferedImage imageResult = null;
// 利用PdfBox生成图像
PDDocument pdDocument = doc;
PDFRenderer renderer = new PDFRenderer(pdDocument);
/*根据总页数, 按照50页生成一张长图片的逻辑, 进行拆分*/
// 每50页转成1张图片
int pageLength = size; //有多少转多少
// 总计循环的次数
int totalCount = pdDocument.getNumberOfPages() / pageLength + 1;
for (int m = 0; m < totalCount; m++) {
for (int i = 0; i < pageLength; i++) {
int pageIndex = i + (m * pageLength);
if (pageIndex == pdDocument.getNumberOfPages()) {
break;
}
// 96为图片的dpi，dpi越大，则图片越清晰，图片越大，转换耗费的时间也越多
BufferedImage image = renderer.renderImageWithDPI(pageIndex, 106, ImageType.RGB);
int imageHeight = image.getHeight();
int imageWidth = image.getWidth();
if (i == 0) {
//计算高度和偏移量
//使用第一张图片宽度;
width = imageWidth;
// 保存每页图片的像素值
// 加个判断：如果m次循环后所剩的图片总数小于pageLength，则图片高度按剩余的张数绘制，否则会出现长图片下面全是黑色的情况
if ((pdDocument.getNumberOfPages() - m * pageLength) < pageLength) {
imageResult = new BufferedImage(width, imageHeight * (pdDocument.getNumberOfPages() - m * pageLength), BufferedImage.TYPE_INT_RGB);
} else {
imageResult = new BufferedImage(width, imageHeight * pageLength, BufferedImage.TYPE_INT_RGB);
}
} else {
// 将高度不断累加
shiftHeight += imageHeight;
}
singleImgRGB = image.getRGB(0, 0, width, imageHeight, null, 0, width);
imageResult.setRGB(0, shiftHeight, width, imageHeight, singleImgRGB, 0, width);
}
// 这个很重要，下面会有说明
shiftHeight = 0;
}
pdDocument.close();
ByteArrayOutputStream baos = new ByteArrayOutputStream();//io流
ImageIO.write(imageResult, "jpg", baos);//写入流中
byte[] jpg_Bytes = baos.toByteArray();//转换成字节
BASE64Encoder encoder = new BASE64Encoder();
jpg_base64 = encoder.encodeBuffer(jpg_Bytes).trim();//转换成base64串
jpg_base64 = jpg_base64.replaceAll("\n", "").replaceAll("\r", "");//删除 \r\n
baos.close();
doc.close();
} catch (IOException e) {
e.printStackTrace();
}
return jpg_base64;
}
以上方法使用到的Maven依赖如下：
<dependency>
<groupId>org.apache.pdfbox</groupId>
<artifactId>pdfbox</artifactId>
<version>2.0.24</version>
</dependency>
<dependency>
<groupId>org.apache.pdfbox</groupId>
<artifactId>fontbox</artifactId>
<version>2.0.24</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-test</artifactId>
</dependency>
有个需要注意到的地方，使用pdfbox转换时，抽象类 NativeFontDirFinder 下的 getSearchableDirectories() 方法指定各个开发平台上字体的存放路径
public abstract class NativeFontDirFinder implements FontDirFinder {
public NativeFontDirFinder() {
}
public List<File> find() {
List<File> fontDirList = new ArrayList();
String[] searchableDirectories = this.getSearchableDirectories();
if (searchableDirectories != null) {
String[] var3 = searchableDirectories;
int var4 = searchableDirectories.length;
for(int var5 = 0; var5 < var4; ++var5) {
String searchableDirectorie = var3[var5];
File fontDir = new File(searchableDirectorie);
try {
if (fontDir.exists() && fontDir.canRead()) {
fontDirList.add(fontDir);
}
} catch (SecurityException var9) {
}
}
}
return fontDirList;
}
protected abstract String[] getSearchableDirectories();
}
Linux平台的字体存放路径如下，转换时需要在会扫描到字体路径中（随便其中一个）存放有需要的字体，否则会有中文丢失不显示，部分字体乱码等情况
public class UnixFontDirFinder extends NativeFontDirFinder {
public UnixFontDirFinder() {
}
protected String[] getSearchableDirectories() {
return new String[]{System.getProperty("user.home") + "/.fonts", "/usr/local/fonts", "/usr/local/share/fonts", "/usr/share/fonts", "/usr/X11R6/lib/X11/fonts", "/usr/share/X11/fonts"};
}
}
3、图片文件压缩，可以调整desFileSize的大小到能接受的文件清晰度，这样做的目的可以降低图片文件大小，以base64在接口间传输时，提高处理速率；
/**
* 根据指定大小压缩图片
*
* @param base64String 源图片base64字符串
* @param desFileSize 指定图片大小，单位kb
* @return 压缩质量后的图片base64字符串
*/
public static String compressPicForScale(String base64String, long desFileSize) {
byte[] imageBytes = Base64.getDecoder().decode(base64String);
if (imageBytes == null || imageBytes.length <= 0 || imageBytes.length < desFileSize * 1024) {
return base64String;
}
long srcSize = imageBytes.length;
double accuracy = getAccuracy(srcSize / 1024);
try {
while (imageBytes.length > desFileSize * 1024) {
ByteArrayInputStream inputStream = new ByteArrayInputStream(imageBytes);
ByteArrayOutputStream outputStream = new ByteArrayOutputStream(imageBytes.length);
Thumbnails.of(inputStream)
.scale(accuracy)
.outputQuality(accuracy)
.toOutputStream(outputStream);
imageBytes = outputStream.toByteArray();
}
log.info("【图片压缩】 | 图片原大小={}kb | 压缩后大小={}kb", srcSize / 1024, imageBytes.length / 1024);
} catch (Exception e) {
log.error("【图片压缩】msg=图片压缩失败!", e);
}
String base64 = Base64.getEncoder().encodeToString(imageBytes);
return base64;
}
/**
* 自动调节精度(经验数值)
*
* @param size 源图片大小
* @return 图片压缩质量比
*/
private static double getAccuracy(long size) {
double accuracy;
if (size < 900) {
accuracy = 0.85;
} else if (size < 2047) {
accuracy = 0.6;
} else if (size < 3275) {
accuracy = 0.44;
} else {
accuracy = 0.4;
}
return accuracy;
}
NativeFontDirFinder
