java中的文件操作：读取写入byte[]字节流、string字符串、list列表

java中文件操作：读取文件成字节流，将字节流写入文件，按行读取文件成字符串列表，将字符串列表存储成文件，读取文件成字符串，将字符串写入文件。

主程序测试文件

//测试程序
public static void main(String[] args) 
{
            byte[] data=file2byte("test.txt");                  //读取文件
    byte2file("test1.txt",data);                        //写入文件
    ArrayList<String> allline=file2list("test.txt","UTF-8");    //按行读取文件
    list2file("test2.txt",allline,"UTF-8");                     //存储文件
    String content=file2str("test.txt","UTF-8");                //读取文件
    str2file("test3.txt",content,"UTF-8");                      //存储文件
}

读取文件成字节数组

public static byte[] file2byte(String path)
{
    try {
        FileInputStream in =new FileInputStream(new File(path));
        //当文件没有结束时，每次读取一个字节显示
        byte[] data=new byte[in.available()];
        in.read(data);
        in.close();
        return data;
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}

将字节数组写入文件

public static void byte2file(String path,byte[] data) {
    try {
        FileOutputStream outputStream  =new FileOutputStream(new File(path));
        outputStream.write(data);
        outputStream.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

按行读取文件成list

public static ArrayList<String> file2list(String path,String encoder) {
    ArrayList<String> alline=new ArrayList<String>();
    try {
        BufferedReader in =new BufferedReader(new InputStreamReader(new FileInputStream(path),encoder));
        String str=new String();
        while ((str=in.readLine())!=null) {
            alline.add(str);
        }
        in.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return alline;
}

输出list到文件

public static void list2file(String path,ArrayList<String> data,String encoder) 
{
    try {
        BufferedWriter out =new BufferedWriter(new OutputStreamWriter(new FileOutputStream(path),encoder));
        for (String str:data) {
            out.write(str);
            out.newLine();
        }
        out.flush();
        out.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

从标准输入中读入

public static String system2str() throws IOException{
    BufferedReader stdin=new BufferedReader(new InputStreamReader(System.in));
    return stdin.readLine();
}

读取文件成字符串

public static String file2str(String path,String encoder) 
{
    StringBuilder sb=new StringBuilder();
    try {
        BufferedReader in =new BufferedReader(new InputStreamReader(new FileInputStream(path),encoder));
        String str=new String();
        while ((str=in.readLine())!=null) {
            sb.append(str);
        }
        in.close(); 
    } catch (Exception e) {
        e.printStackTrace();
    }
    return sb.toString();
}

输出字符串到文件

public static void str2file(String path,String data,String encoder) 
{
    try {
        BufferedWriter out =new BufferedWriter(new OutputStreamWriter(new FileOutputStream(path),encoder));
        out.write(data);
        out.flush();
        out.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

读取文件成数据矩阵

public static ArrayList<Double> file2matrix(String path) 
{
    ArrayList<Double> alldata=new ArrayList<Double>();
    try {
        DataInputStream in=new DataInputStream(new BufferedInputStream(new FileInputStream(path)));
        //利用DataInputStream来读数据
        while(true)
        {
            alldata.add(in.readDouble());
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return alldata;
}

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原文链接：https://blog.youkuaiyun.com/luanpeng825485697/article/details/78148472