如何将java.io.File
转换为byte[]
?
这取决于什么最好的方法为您服务。生产力明智的,不推倒重来,并使用Apache的百科全书。这是在这里IOUtils.toByteArray(InputStream input)
。
简单的方法来做到这一点:
File fff = new File("/path/to/file");
FileInputStream fileInputStream = new FileInputStream(fff);
// int byteLength = fff.length();
// In android the result of file.length() is long
long byteLength = fff.length(); // byte count of the file-content
byte[] filecontent = new byte[(int) byteLength];
fileInputStream.read(filecontent, 0, (int) byteLength);
从文件中读取字节的最简单方法
import java.io.*;
class ReadBytesFromFile {
public static void main(String args[]) throws Exception {
// getBytes from anyWhere
// I'm getting byte array from File
File file = null;
FileInputStream fileStream = new FileInputStream(file = new File("ByteArrayInputStreamClass.java"));
// Instantiate array
byte[] arr = new byte[(int) file.length()];
// read All bytes of File stream
fileStream.read(arr, 0, arr.length);
for (int X : arr) {
System.out.print((char) X);
}
}
}
番石榴Files.toByteArray()向你提供。它具有以下几个优点:
import java.io.File;
import java.nio.file.Files;
import java.nio.file.Path;
File file = getYourFile();
Path path = file.toPath();
byte[] data = Files.readAllBytes(path);
使用相同的方法作为社会维基答案,但清洁和编译开箱即用(首选的方法,如果你不希望导入的Apache共享库,例如在Android上):
public static byte[] getFileBytes(File file) throws IOException {
ByteArrayOutputStream ous = null;
InputStream ios = null;
try {
byte[] buffer = new byte[4096];
ous = new ByteArrayOutputStream();
ios = new FileInputStream(file);
int read = 0;
while ((read = ios.read(buffer)) != -1)
ous.write(buffer, 0, read);
} finally {
try {
if (ous != null)
ous.close();
} catch (IOException e) {
// swallow, since not that important
}
try {
if (ios != null)
ios.close();
} catch (IOException e) {
// swallow, since not that important
}
}
return ous.toByteArray();
}
我相信这是最简单的方法:
org.apache.commons.io.FileUtils.readFileToByteArray(file);
的readFully从此文件读取b.length个字节到字节数组,并从当前文件指针。直到字节的请求数量是读这个方法从文件重复读取。此方法一直阻塞请求的字节数被读出,当检测到流的末尾,或抛出异常。
RandomAccessFile f = new RandomAccessFile(fileName, "r");
byte[] b = new byte[(int)f.length()];
f.readFully(b);
让我补充另一种解决方案,而无需使用第三方库。它重新使用已提出Scott(link)的异常处理模式。我提出的难看部分到一个单独的消息(I将隐藏在一些文件实用程序类;))
public void someMethod() {
final byte[] buffer = read(new File("test.txt"));
}
private byte[] read(final File file) {
if (file.isDirectory())
throw new RuntimeException("Unsupported operation, file "
+ file.getAbsolutePath() + " is a directory");
if (file.length() > Integer.MAX_VALUE)
throw new RuntimeException("Unsupported operation, file "
+ file.getAbsolutePath() + " is too big");
Throwable pending = null;
FileInputStream in = null;
final byte buffer[] = new byte[(int) file.length()];
try {
in = new FileInputStream(file);
in.read(buffer);
} catch (Exception e) {
pending = new RuntimeException("Exception occured on reading file "
+ file.getAbsolutePath(), e);
} finally {
if (in != null) {
try {
in.close();
} catch (Exception e) {
if (pending == null) {
pending = new RuntimeException(
"Exception occured on closing file"
+ file.getAbsolutePath(), e);
}
}
}
if (pending != null) {
throw new RuntimeException(pending);
}
}
return buffer;
}
如果要读取的字节为预分配字节的缓冲区,这个答案可能会有所帮助。
你的第一个猜测可能是使用InputStream read(byte[])
。然而,这种方法有一个缺陷,它使不合理难用:不保证该阵列实际上完全充满,即使没有遇到EOF。
相反,看看DataInputStream readFully(byte[])
。这是输入流的包装,并且不具有上述问题。此外,遇到时EOF此方法抛出。更好。
public static byte[] readBytes(InputStream inputStream) throws IOException {
byte[] buffer = new byte[32 * 1024];
int bufferSize = 0;
for (;;) {
int read = inputStream.read(buffer, bufferSize, buffer.length - bufferSize);
if (read == -1) {
return Arrays.copyOf(buffer, bufferSize);
}
bufferSize += read;
if (bufferSize == buffer.length) {
buffer = Arrays.copyOf(buffer, bufferSize * 2);
}
}
}
从JDK 7,您可以使用Files.readAllBytes(Path)
。
例:
import java.io.File;
import java.nio.file.Files;
File file;
// ...(file is initialised)...
byte[] fileContent = Files.readAllBytes(file.toPath());
另一种方式从文件中读取的字节
Reader reader = null;
try {
reader = new FileReader(file);
char buf[] = new char[8192];
int len;
StringBuilder s = new StringBuilder();
while ((len = reader.read(buf)) >= 0) {
s.append(buf, 0, len);
byte[] byteArray = s.toString().getBytes();
}
} catch(FileNotFoundException ex) {
} catch(IOException e) {
}
finally {
if (reader != null) {
reader.close();
}
}
不仅通过以下方式转换的java.io.File到一个byte [],我还发现它是在一个文件中读取最快的方式,互相测试许多不同Java file reading methods时:
java.nio.file.Files.readAllBytes()
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
public class ReadFile_Files_ReadAllBytes {
public static void main(String [] pArgs) throws IOException {
String fileName = "c:\\temp\\sample-10KB.txt";
File file = new File(fileName);
byte [] fileBytes = Files.readAllBytes(file.toPath());
char singleChar;
for(byte b : fileBytes) {
singleChar = (char) b;
System.out.print(singleChar);
}
}
}
尝试这个 :
try
{
String path="";
InputStream inputStream=new FileInputStream(path);
byte[] data=IOUtils.readFully(inputStream,-1,false);
}
catch (Exception e)
{
}
不要忘了“进口sun.misc.IOUtils;”
在JDK8
Stream<String> lines = Files.lines(path);
String data = lines.collect(Collectors.joining("\n"));
lines.close();
由于JDK 7 - 一个内胆:
byte[] array = Files.readAllBytes(Paths.get("/path/to/file"));
无需外部依赖性所需。
import java.io.RandomAccessFile;
RandomAccessFile f = new RandomAccessFile(fileName, "r");
byte[] b = new byte[(int)f.length()];
f.readFully(b);
文档为Java 8:http://docs.oracle.com/javase/8/docs/api/java/io/RandomAccessFile.html
基本上,你必须在内存中读取它。打开文件时,分配的阵列,且从文件到阵列读取的内容。
最简单的方法是类似这样的:
public byte[] read(File file) throws IOException, FileTooBigException {
if (file.length() > MAX_FILE_SIZE) {
throw new FileTooBigException(file);
}
ByteArrayOutputStream ous = null;
InputStream ios = null;
try {
byte[] buffer = new byte[4096];
ous = new ByteArrayOutputStream();
ios = new FileInputStream(file);
int read = 0;
while ((read = ios.read(buffer)) != -1) {
ous.write(buffer, 0, read);
}
}finally {
try {
if (ous != null)
ous.close();
} catch (IOException e) {
}
try {
if (ios != null)
ios.close();
} catch (IOException e) {
}
}
return ous.toByteArray();
}
这具有这样的文件内容(实际上是数据被复制三次:从文件buffer
,从buffer
到ByteArrayOutputStream
,从ByteArrayOutputStream
实际得到的阵列)的一些不必要的复制。
你还需要确保你在内存只读文件备份到一定规模(这通常是依赖于应用程序):-)。
您还需要治疗功能外IOException
。
另一种方法是这样的:
public byte[] read(File file) throws IOException, FileTooBigException {
if (file.length() > MAX_FILE_SIZE) {
throw new FileTooBigException(file);
}
byte[] buffer = new byte[(int) file.length()];
InputStream ios = null;
try {
ios = new FileInputStream(file);
if (ios.read(buffer) == -1) {
throw new IOException(
"EOF reached while trying to read the whole file");
}
} finally {
try {
if (ios != null)
ios.close();
} catch (IOException e) {
}
}
return buffer;
}
这有没有不必要的复制。
FileTooBigException
是一个自定义的应用程序异常。所述MAX_FILE_SIZE
常数是一个应用程序的参数。
对于大文件,你应该想到流处理算法或使用内存映射(见java.nio
)。
正如有人所说,Apache Commons File Utils可能有你在找什么
public static byte[] readFileToByteArray(File file) throws IOException
实施例使用(Program.java
):
import org.apache.commons.io.FileUtils;
public class Program {
public static void main(String[] args) throws IOException {
File file = new File(args[0]); // assume args[0] is the path to file
byte[] data = FileUtils.readFileToByteArray(file);
...
}
}
您可以使用NIO API,以及这样做。我可以用这个代码做到这一点,只要总文件大小(以字节为单位)将适合用int表示。
File f = new File("c:\\wscp.script");
FileInputStream fin = null;
FileChannel ch = null;
try {
fin = new FileInputStream(f);
ch = fin.getChannel();
int size = (int) ch.size();
MappedByteBuffer buf = ch.map(MapMode.READ_ONLY, 0, size);
byte[] bytes = new byte[size];
buf.get(bytes);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
if (fin != null) {
fin.close();
}
if (ch != null) {
ch.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
我想,因为它的使用MappedByteBuffer它的速度非常快。
如果你没有的Java 8,并同意我的说法,包括一个巨大的图书馆,以避免写的几行代码是一个坏主意:
public static byte[] readBytes(InputStream inputStream) throws IOException {
byte[] b = new byte[1024];
ByteArrayOutputStream os = new ByteArrayOutputStream();
int c;
while ((c = inputStream.read(b)) != -1) {
os.write(b, 0, c);
}
return os.toByteArray();
}
来电者负责关闭该流。
// Returns the contents of the file in a byte array.
public static byte[] getBytesFromFile(File file) throws IOException {
// Get the size of the file
long length = file.length();
// You cannot create an array using a long type.
// It needs to be an int type.
// Before converting to an int type, check
// to ensure that file is not larger than Integer.MAX_VALUE.
if (length > Integer.MAX_VALUE) {
// File is too large
throw new IOException("File is too large!");
}
// Create the byte array to hold the data
byte[] bytes = new byte[(int)length];
// Read in the bytes
int offset = 0;
int numRead = 0;
InputStream is = new FileInputStream(file);
try {
while (offset < bytes.length
&& (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
offset += numRead;
}
} finally {
is.close();
}
// Ensure all the bytes have been read in
if (offset < bytes.length) {
throw new IOException("Could not completely read file "+file.getName());
}
return bytes;
}