原文地址：（英文版）
https://howtodoinjava.com/core-java/io/java-read-file-to-string-examples/
Learn to read file to string in java. Examples use Files.readAllBytes, Files.lines and FileReader & BufferedReader to read file content.
学习读取文件,并赋值到String中。 示例使用
- Files.readAllBytes
- Files.lines
- FileReader＆BufferedReader
读取文件内容。
Source code of all 3 examples for reading files into string.
三种方法读文件方法的源代码
//Example 1
//Read file content into string with - Files.lines(Path path, Charset cs)
private static String readLineByLineJava8(String filePath)
{
StringBuilder contentBuilder = new StringBuilder();
try (Stream stream = Files.lines(
Paths.get(filePath), StandardCharsets.UTF_8))
{
stream.forEach(s -> contentBuilder.append(s).append("\n"));
}
catch (IOException e)
{
e.printStackTrace();
}
return contentBuilder.toString();
}
//Example 2
//Read file content into string with - Files.readAllBytes(Path path)
private static String readAllBytesJava7(String filePath)
{
String content = "";
try
{
content = new String ( Files.readAllBytes( Paths.get(filePath) ) );
}
catch (IOException e)
{
e.printStackTrace();
}
return content;
}
//Example 3
//Read file content into string with - using BufferedReader and FileReader
//You can use this if you are still not using Java 8
private static String usingBufferedReader(String filePath)
{
StringBuilder contentBuilder = new StringBuilder();
try (BufferedReader br = new BufferedReader(new FileReader(filePath)))
{
String sCurrentLine;
while ((sCurrentLine = br.readLine()) != null)
{
contentBuilder.append(sCurrentLine).append("\n");
}
}
catch (IOException e)
{
e.printStackTrace();
}
return contentBuilder.toString();
}
I have placed a file data.txt at location c:/temp. I will read this file in all 3 examples.
准备一个文件，文件名为data.txt，放到c:/temp目录下面，然后会用三种方法把文件内容读出来
File content in c:/temp/data.txt
文件内容如下
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Read File to String using Files.lines() [≥ Java 8]
使用Files.lines()读取文件，需要JDK版本为Java 8 以上
lines() method read all lines from a file to stream and populates lazily as the stream is consumed. Bytes from the file are decoded into characters using the specified charset.
lines（）方法从文件中读取所有行，通过流（stream）的方式读到内存。 使用指定的字符集将文件中的二进制字节解码转换为字符。
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Stream;
public class ReadFileToString
{
public static void main(String[] args)
{
String filePath = "c:/temp/data.txt";
System.out.println( readLineByLineJava8( filePath ) );
}
//Read file content into string with - Files.lines(Path path, Charset cs)
private static String readLineByLineJava8(String filePath)
{
StringBuilder contentBuilder = new StringBuilder();
try (Stream stream = Files.lines(
Paths.get(filePath), StandardCharsets.UTF_8))
{
stream.forEach(s -> contentBuilder.append(s).append("\n"));
}
catch (IOException e)
{
e.printStackTrace();
}
return contentBuilder.toString();
}
}
打开你的IDE，COPY下面代码，然后运行，就可以在控制台看到输出
使用Files.readAllBytes()读取文件，需要JDK版本为Java 7 以上
Read File to String using Files.readAllBytes() [≥ Java 7]
readAllBytes() method 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.
After reading all bytes, we pass those bytes toStringclass constructor to create a string.
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
public class ReadFileToString
{
public static void main(String[] args)
{
String filePath = "c:/temp/data.txt";
System.out.println( readAllBytesJava7( filePath ) );
}
//Read file content into string with - Files.readAllBytes(Path path)
private static String readAllBytesJava7(String filePath)
{
String content = "";
try
{
content = new String ( Files.readAllBytes( Paths.get(filePath) ) );
}
catch (IOException e)
{
e.printStackTrace();
}
return content;
}
}
Read File to String using BufferedReader [< Java 7]
使用BufferedReader 读取文件，最老的方式
If you are still not using java 7 or later, then use BufferedReader class. It’sreadLine()method reads the file one line at a time and return the content.
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class ReadFileToString
{
public static void main(String[] args)
{
String filePath = "c:/temp/data.txt";
System.out.println( usingBufferedReader( filePath ) );
}
//Read file content into string with - using BufferedReader and FileReader
//You can use this if you are still not using Java 8
private static String usingBufferedReader(String filePath)
{
StringBuilder contentBuilder = new StringBuilder();
try (BufferedReader br = new BufferedReader(new FileReader(filePath)))
{
String sCurrentLine;
while ((sCurrentLine = br.readLine()) != null)
{
contentBuilder.append(sCurrentLine).append("\n");
}
}
catch (IOException e)
{
e.printStackTrace();
}
return contentBuilder.toString();
}
}