java读取文件内容为字符串

Java 11 - Files.readString()

java 11 提供了readString()方法，只需一行就能读取文件内容为字符串。

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
 
public class WriteToFile 
{
    public static void main(String[] args) throws IOException 
    {
        Path fileName = Path.of("demo.txt");
        String content  = "hello world !!";
        Files.writeString(fileName, content);
         
        String actual = Files.readString(fileName);
        System.out.println(actual);
    }
}

Java 8 - Files.lines()

lines()方法会从文件读取所有行到流。

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<String> 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();
    }
}

Java 7 - Files.readAllBytes()

readAllBytes()方法从文件中读取所有字节。

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;
    }
}

Java 6 - BufferedReader

BufferedReader一行行读文件。

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();
    }
}