全棧工程師開發手冊 （作者：欒鵬）

java中檔案操作：讀取檔案成位元組流，將位元組流寫入檔案，按行讀取檔案成字串列表，將字串列表儲存成檔案，讀取檔案成字串，將字串寫入檔案。

主程式測試檔案

    //測試程式
    public static void main(String[] args) 
    {
                byte[] data=file2byte("test.txt");                  //讀取檔案
        byte2file("test1.txt",data);                        //寫入檔案
 

        ArrayList<String> allline=file2list("test.txt","UTF-8");    //按行讀取檔案
        list2file("test2.txt",allline,"UTF-8");                     //儲存檔案
        String content=file2str("test.txt","UTF-8");                //讀取檔案
        str2file("test3.txt",content,"UTF-8");                      //儲存檔案
 

    }

讀取檔案成位元組陣列

    public static byte[] file2byte(String path)
    {
        try {
            FileInputStream in =new FileInputStream(new File(path));
            //當檔案沒有結束時，每次讀取一個位元組顯示
            byte[] data=new byte[in.available()];
            in.read(data);
            in.close();
            return
 
 data;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

將位元組陣列寫入檔案

    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();
        }
    }

按行讀取檔案成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;
    }

輸出list到檔案

    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();
        }
    }

從標準輸入中讀入

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

讀取檔案成字串

    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();
    }

輸出字串到檔案

    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();
        }
    }

讀取檔案成資料矩陣

    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來讀資料
            while(true)
            {
                alldata.add(in.readDouble());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return alldata;
    }