JDK1.7中引入了新的文件操作類java.nio.file這個包，其中有個Files類它包含了很多有用的方法來操作文件，比如檢查文件是否為隱藏文件，或者是檢查文件是否為只讀文件。開發者還可以使用Files.readAllBytes(Path)方法把整個文件讀入內存，此方法返回一個字節數組，還可以把結果傳遞給String的構造器，以便創建字符串輸出。此方法確保了當讀入文件的所有字節內容時，無論是否出現IO異常或其它的未檢查異常，資源都會關閉。這意味著在讀文件到最后的塊內容后，無需關閉文件。要注意，此方法不適合讀取很大的文件，因為可能存在內存空間不足的問題。開發者還應該明確規定文件的字符編碼，以避免任異常或解析錯誤。
readAllBytes(Path)方法的源碼：
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<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. * 注意該方法只適用于簡單的情況，這種簡單的情況能夠很方便地將所有的字節讀進一個字節數組，但并不適合用來讀取大文件 * <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，將拋出內存溢出異常 * @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> |
讀取文件只要一行
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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方法的源碼
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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; } } |
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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這么讀 調用readAllLines 方法 try {<span style="white-space:pre"> </span>//JDK1.8以后可以省略第二個參數，默認是UTF-8編碼 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 換行符 } String fromFile = sb.toString(); System.out.println(fromFile); } catch (IOException e) { e.printStackTrace(); } } } |
使用Java8 流的方式：
先看源碼實現
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public static Stream<String> lines(Path path) throws IOException { return lines(path, StandardCharsets.UTF_8); } |
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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用流的方式讀文件，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(); } } } |
讀文件一行寫文件也只需要一行
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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用流的方式讀文件，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)方法返回值為List<String>類型，就是為Files.write()而設計的 * 因為Files.write()需要傳入一個Iterable<? extends CharSequence>類型的參數 * * Files.write(Path path, Iterable<? extends CharSequence> lines, OpenOption... options) */ List<String> stringStream=Files.readAllLines(Paths.get(filePath)); //因為Files.lines(Path path)返回的是Stream<String>,所以可以通過下面這種方法變成List<String> //List<String> stringStream2=Arrays.asList((String[])Files.lines(Paths.get(filePath)).toArray()); //StandardOpenOption為枚舉類 ,如果當前所Paths.get()的文件不存在，第三個參數可選擇StandardOpenOption.CREATE_NEW //文件存在則拋java.nio.file.FileAlreadyExistsException異常 Files.write(Paths.get("C:\\2.java"), stringStream, StandardOpenOption.CREATE_NEW); } catch (IOException e) { e.printStackTrace(); } } } |
以上這篇JDK1.7 之java.nio.file.Files 讀取文件僅需一行代碼實現就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支持服務器之家。
原文鏈接：http://blog.csdn.net/ljh_learn_from_base/article/details/77760039
