InputStream转String高效实现
时间: 2023-07-07 10:27:25 浏览: 48
可以使用Java 8中的java.util.Scanner类将InputStream转换为String,代码如下:
```
import java.util.Scanner;
import java.io.InputStream;
import java.util.NoSuchElementException;
import java.util.Locale;
public String inputStreamToString(InputStream inputStream) {
Scanner scanner = new Scanner(inputStream).useDelimiter("\\A");
try {
return scanner.hasNext() ? scanner.next() : "";
} catch (NoSuchElementException e) {
return "";
}
}
```
这里使用了Scanner类的useDelimiter方法,将输入流的分隔符设置为正则表达式“\\A”,也就是输入的开头。这样,在调用Scanner的next方法时,就会把整个输入流读取为一个字符串。同时,为了避免NoSuchElementException异常的出现,我们需要在try-catch语句中处理这个异常。
相关问题
java高效excel转pdf
要实现Java高效地将Excel文件转换为PDF文件,可以使用Apache POI和iText库来完成。下面是一个简单的示例代码:
```
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import com.itextpdf.text.Document;
import com.itextpdf.text.PageSize;
import com.itextpdf.text.pdf.PdfWriter;
import com.itextpdf.text.pdf.codec.Base64.InputStream;
public class ExcelToPDFConverter {
public static void main(String[] args) throws IOException {
String excelFilePath = "path/to/excel/file.xlsx";
String pdfFilePath = "path/to/pdf/file.pdf";
Workbook workbook = null;
if (excelFilePath.endsWith(".xls")) {
workbook = new HSSFWorkbook(new FileInputStream(excelFilePath));
} else if (excelFilePath.endsWith(".xlsx")) {
workbook = new XSSFWorkbook(new FileInputStream(excelFilePath));
}
Document document = new Document();
PdfWriter.getInstance(document, new FileOutputStream(pdfFilePath));
document.open();
for (int i = 0; i < workbook.getNumberOfSheets(); i++) {
document.newPage();
InputStream inputStream = new InputStream(workbook.getSheetAt(i).getRow(0).getCell(0).getStringCellValue().getBytes());
com.itextpdf.text.Image image = com.itextpdf.text.Image.getInstance(inputStream);
image.scaleToFit(PageSize.A4.getWidth(), PageSize.A4.getHeight());
document.add(image);
}
document.close();
workbook.close();
System.out.println("PDF file generated successfully!");
}
}
```
这段代码将Excel文件读取到Workbook对象中,然后使用iText库创建一个PDF文档并添加Excel文件中的每个工作表作为PDF页面。最后,将PDF文档保存到指定的文件路径中。
请注意,这只是一个基本示例,您可能需要根据您的具体需求进行更改和优化。
java代码实现上传下载视频高效方法
实现上传下载视频的高效方法,可以考虑以下几点:
1. 使用多线程:多线程能够充分利用带宽,加快上传下载速度。可以使用Java的线程池来管理线程,避免线程过多导致系统资源耗尽。
2. 分块传输:将大文件分成若干个块进行传输,这样即使某一块传输失败,也不会影响整个文件的上传或下载。可以使用HTTP协议的分块传输编码(Chunked Transfer Encoding)或者自定义分块传输协议。
3. 压缩数据:对于大文件,可以在传输时进行压缩,减少传输数据量。可以使用Java的压缩库(如GZIP)进行压缩。
4. 使用CDN:通过使用CDN(内容分发网络),可以将静态资源缓存到离用户最近的节点上,加速文件的传输。
下面是Java代码实现上传下载视频的示例:
上传视频:
```java
File file = new File("video.mp4");
String url = "http://example.com/upload";
CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost httpPost = new HttpPost(url);
//分块上传
FileEntity fileEntity = new FileEntity(file, ContentType.DEFAULT_BINARY);
httpPost.setEntity(fileEntity);
//设置多线程上传
ExecutorService executorService = Executors.newFixedThreadPool(5); //开启5个线程
List<Future> futures = new ArrayList<>();
for (int i = 0; i < 5; i++) { //将文件分成5块并上传
final int partNumber = i+1;
final long start = i * file.length() / 5;
final long end = (i+1) * file.length() / 5 - 1;
Future<?> future = executorService.submit(() -> {
HttpPost httpPartPost = new HttpPost(url);
httpPartPost.setHeader("Content-Range", "bytes " + start + "-" + end + "/" + file.length());
httpPartPost.setEntity(new FileEntity(file, ContentType.DEFAULT_BINARY, start, end));
CloseableHttpResponse response = httpClient.execute(httpPartPost);
response.close();
});
futures.add(future);
}
//等待所有线程上传完成
for (Future future : futures) {
try {
future.get();
} catch (Exception e) {
e.printStackTrace();
}
}
executorService.shutdown();
httpClient.close();
```
下载视频:
```java
String url = "http://example.com/video.mp4";
CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet(url);
//设置多线程下载
ExecutorService executorService = Executors.newFixedThreadPool(5); //开启5个线程
List<Future> futures = new ArrayList<>();
CloseableHttpResponse response = httpClient.execute(httpGet);
long contentLength = Long.parseLong(response.getFirstHeader("Content-Length").getValue());
for (int i = 0; i < 5; i++) { //将文件分成5块并下载
final int partNumber = i+1;
final long start = i * contentLength / 5;
final long end = (i+1) * contentLength / 5 - 1;
Future<?> future = executorService.submit(() -> {
HttpGet httpPartGet = new HttpGet(url);
httpPartGet.setHeader("Range", "bytes=" + start + "-" + end);
CloseableHttpResponse partResponse = httpClient.execute(httpPartGet);
HttpEntity entity = partResponse.getEntity();
InputStream inputStream = entity.getContent();
FileOutputStream fileOutputStream = new FileOutputStream("video_" + partNumber + ".mp4");
byte[] buffer = new byte[1024];
int len;
while ((len = inputStream.read(buffer)) != -1) {
fileOutputStream.write(buffer, 0, len);
}
fileOutputStream.close();
inputStream.close();
partResponse.close();
});
futures.add(future);
}
//等待所有线程下载完成
for (Future future : futures) {
try {
future.get();
} catch (Exception e) {
e.printStackTrace();
}
}
executorService.shutdown();
httpClient.close();
```