JDK1.7中引入了新的文件操作类java.nio.file这个包，其中有个Files类它包含了很多有用的方法来操作文件，比如检查文件是否为隐藏文件，或者是检查文件是否为只读文件。开发者还可以使用Files.readAllBytes(Path)方法把整个文件读入内存，此方法返回一个字节数组，还可以把结果传递给String的构造器，以便创建字符串输出。此方法确保了当读入文件的所有字节内容时，无论是否出现IO异常或其它的未检查异常，资源都会关闭。这意味着在读文件到最后的块内容后，无需关闭文件。要注意，此方法不适合读取很大的文件，因为可能存在内存空间不足的问题。开发者还应该明确规定文件的字符编码，以避免任异常或解析错误。
readAllBytes(Path)方法的源码：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
|
<span style="font-size:32px;"> </span><span style="font-size:18px;">/** * Reads all the bytes from a file. The method ensures that the file is * closed when all bytes have been read or an I/O error, or other runtime * exception, is thrown. * 注意该方法只适用于简单的情况，这种简单的情况能够很方便地将所有的字节读进一个字节数组，但并不适合用来读取大文件 * <p> Note that this method is intended for simple cases where it is * convenient to read all bytes into a byte array. It is not intended for * reading in large files. * * @param path * the path to the file * * @return a byte array containing the bytes read from the file * * @throws IOException * if an I/O error occurs reading from the stream * 如果大于文件2G，将抛出内存溢出异常 * @throws OutOfMemoryError * if an array of the required size cannot be allocated, for * example the file is larger that {@code 2GB} * @throws SecurityException * In the case of the default provider, and a security manager is * installed, the {@link SecurityManager#checkRead(String) checkRead} * method is invoked to check read access to the file. */</span><span style="font-size:18px;"> public static byte[] readAllBytes(Path path) throws IOException { try (SeekableByteChannel sbc = Files.newByteChannel(path); InputStream in = Channels.newInputStream(sbc)) {//JDK1.7 try-with-resource long size = sbc.size(); if (size > (long)MAX_BUFFER_SIZE) throw new OutOfMemoryError("Required array size too large"); return read(in, (int)size); } }</span> |
读取文件只要一行
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
|
package entryNIO; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; public class BufferAndChannel { public static void main(String[] args) { try { System.out.println( new String(Files.readAllBytes(Paths.get("C:\\FileChannelImpl.java"))) ); } catch (IOException e) { e.printStackTrace(); } } } |
readAllLines方法的源码
|
1
2
3
4
5
6
7
8
9
10
11
12
|
public static List<String> readAllLines(Path path, Charset cs) throws IOException { try (BufferedReader reader = newBufferedReader(path, cs)) { List<String> result = new ArrayList<>(); for (;;) { String line = reader.readLine(); if (line == null) break; result.add(line); } return result; } } |
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
|
package entryNIO; import java.util.List; import java.io.IOException; import java.nio.charset.StandardCharsets; import java.nio.file.Files; import java.nio.file.Paths; public class BufferAndChannel { public static void main(String[] args) { //如果是文本文件也可以这么读 调用readAllLines 方法 try {<span style="white-space:pre"> </span>//JDK1.8以后可以省略第二个参数，默认是UTF-8编码 List<String> lines = Files.readAllLines(Paths.get("C:\\FileChannelImpl.java"), StandardCharsets.UTF_8); StringBuilder sb = new StringBuilder(); for (String line : lines) { sb.append(line+"\n");// \r\n 换行符 } String fromFile = sb.toString(); System.out.println(fromFile); } catch (IOException e) { e.printStackTrace(); } } } |
使用Java8 流的方式：
先看源码实现
|
1
2
3
|
public static Stream<String> lines(Path path) throws IOException { return lines(path, StandardCharsets.UTF_8); } |
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
|
package entryNIO; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; public class BufferAndChannel { public static void main(String[] args) { //Java8 新增lines方法 try { // Java8用流的方式读文件，更加高效 Files.lines(Paths.get(<span style="font-family: Arial, Helvetica, sans-serif;">"C:\\FileChannelImpl.java"</span>)).forEach(System.out::println); } catch (IOException e) { e.printStackTrace(); } } } |
读文件一行写文件也只需要一行
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
|
package entryNIO; import java.util.Arrays; import java.util.List; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; import java.nio.file.StandardOpenOption; public class BufferAndChannel { public static void main(String[] args){ //Java8 新增lines方法 String filePath="C:\\FileChannelImpl.java"; try { // Java8用流的方式读文件，更加高效 /*Files.lines(Paths.get(filePath)).forEach((line)->{ try { Files.write(Paths.get("\\1.java"), line.getBytes(), StandardOpenOption.APPEND); //Files.copy(in, target, options); } catch (IOException e) { e.printStackTrace(); } }); */ /* Files.readAllLines(Path path)方法返回值为List<String>类型，就是为Files.write()而设计的 * 因为Files.write()需要传入一个Iterable<? extends CharSequence>类型的参数 * * Files.write(Path path, Iterable<? extends CharSequence> lines, OpenOption... options) */ List<String> stringStream=Files.readAllLines(Paths.get(filePath)); //因为Files.lines(Path path)返回的是Stream<String>,所以可以通过下面这种方法变成List<String> //List<String> stringStream2=Arrays.asList((String[])Files.lines(Paths.get(filePath)).toArray()); //StandardOpenOption为枚举类 ,如果当前所Paths.get()的文件不存在，第三个参数可选择StandardOpenOption.CREATE_NEW //文件存在则抛java.nio.file.FileAlreadyExistsException异常 Files.write(Paths.get("C:\\2.java"), stringStream, StandardOpenOption.CREATE_NEW); } catch (IOException e) { e.printStackTrace(); } } } |
以上这篇JDK1.7 之java.nio.file.Files 读取文件仅需一行代码实现就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：http://blog.csdn.net/ljh_learn_from_base/article/details/77760039
