JDK1.7 之java.nio.file.Files 读取文件仅需一行代码实现

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：

<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

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

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; 
    } 
  } 

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

public static stream<string> lines(path path) throws ioexception { 
    return lines(path, standardcharsets.utf_8); 
  } 

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

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。