java-io-总结-代码-1

/**
 * 以程序为主体
 * 以文件为目的地，进行输入输出，修改，删除等操作
 * out write为输出信息，也是向文件中写入东西的意思。  将信息存入目的地

 * in read为输入信息，读取文件内容，然后展示在我们控制台。  从目的地获得信息
 */

 

创建一个新txt文件

/**
     * 创建一个新文件
     */
    @Test
    public void test1() {
        File f = new File("D:\\hello.txt");
        try {
            f.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

 

 

File的两个常量，有的在os不同的时候是不一样的。

@Test
    public void test2() {
        System.out.println(File.separator);
        System.out.println(File.pathSeparator);
    }

增强代码可用性

@Test
    public void test3() {
        String fileName = "D:" + File.separator + "hello1.txt";
        File f = new File(fileName);
        try {
            f.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

 

删除一个txt文件

 @Test
    public void test4() {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        if (f.exists()) {
            f.delete();
        } else {
            System.out.println(fileName + "改文件不存在");
        }
    }

 

列出指定目录全部文件，包括隐藏文件

@Test
    public void test5() {
        String fileName = "D:" + File.separator;
        File f = new File(fileName);
        String[] strings = f.list();
        for (int i = 0; i < strings.length; i++) {
            System.out.println(strings[i]);
        }
        System.out.println(strings.length);
    }

 

 

列出指定目录的所有文件，包含隐含文件，列出的方式是
* 展现所有目录的完整路径

@Test
    public void test6() {
        String fileName = "D:" + File.separator;
        File f = new File(fileName);
        File[] files = f.listFiles();
        for (int i = 0; i < files.length; i++) {
            System.out.println(files[i]);
        }
        System.out.println(files.length);
    }

 

判断指定路径是不是真实路径

@Test
    public void test7() {
        String fileName = "D:" + File.separator;
        File f = new File(fileName);
        if (f.isDirectory()) {
            System.out.println(fileName + "是真实路径");
        } else {
            System.out.println(fileName + "不是真实路径");
        }
    }

 

打印出指定目录的全部内容，完整路径。-----递归

@Test
    public void test8() {
//        String fileName = "D:"+File.separator;
        String fileName = "D:\\640808\\shenshaonian\\Program Files-fan";
        File f = new File(fileName);
        printf(f);
    }

    public static void printf(File f) {
        if (null != f) {
            if (f.isDirectory()) {
                File[] files = f.listFiles();
                if (null != files) {
                    for (int i = 0; i < files.length; i++) {
                        printf(files[i]);
                    }
                }
            } else {
                System.out.println(f);
            }
        }
    }

 

使用RandomAccessFile写入文件，结果发现是乱码

 public void test9() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        RandomAccessFile demo = new RandomAccessFile(f, "rw");
        demo.writeBytes("randomAccessFile写入");
        demo.writeInt(12);
        demo.writeBoolean(true);
        demo.writeChar('A');
        demo.writeFloat(1.21f);
        demo.writeDouble(12.123);
        demo.close();
    }

原因https://www.cnblogs.com/kakaisgood/p/8857885.html

按字节序列将该字符串写入该文件。该字符串中的每个字符均按顺序写出，并丢弃其高八位。写入从文件指针的当前位置开始

问题出在writeBytes(String s)这个方法上。

JAVA中的char是16位的，一个char存储一个中文字符，直接用writeBytes方法转换会变为8位，直接导致高8位丢失。从而导致中文乱码。

 乱码的原因和解决方案

 public void test9() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        RandomAccessFile demo = new RandomAccessFile(f, "rw");
//        String s = "randomAccessFile写入";
//        demo.write(s.getBytes());
//        demo.write("randomAccessFile写入fdasf".getBytes());

//        int i = 12;
//        String ii = Integer.valueOf(i).toString();
//        demo.write(ii.getBytes());
        double db = 12.123;
        demo.write(Double.valueOf(db).toString().getBytes());

//        demo.writeBytes("randomAccessFile写入");
// JAVA中的char是16位的，一个char存储一个中文字符，直接用writeBytes方法转换会变为8位，
// 直接导致高8位丢失。从而导致中文乱码。
//        解决方法：
//        现转换为字节组，再write写入流。

//        demo.writeInt(12);int使用的是一个4个字节保存的，想显示出来必须转换为字符串。。。
//        demo.writeBoolean(true);  占8字节，写进去是什么都没显示的，可读取出来，代码如下
//        demo.writeChar('A');
//        demo.writeFloat(1.21f);4字节，转string，按字节写入
//        demo.writeDouble(12.123);，8字节



        demo.close();


//        //写入写入boolean
//        boolean b = true;
//        // create a new RandomAccessFile with filename test
//        RandomAccessFile raf = new RandomAccessFile("d:/test11.txt", "rw");
//        // write a boolean
//        raf.writeBoolean(false);
//        // set the file pointer at 0 position
//        raf.seek(0);
//        // print the boolean
//        System.out.println("" + raf.readBoolean());
//        // write a boolean
//        raf.writeBoolean(b);
//        // set the file pointer at position 1
//        raf.seek(1);
//        // print the boolean
//        System.out.println("" + raf.readBoolean());
    }

 

 

FileOutputStream向文件中写入字符串，结果 正常显示

@Test
    public void test10() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        OutputStream out = new FileOutputStream(f);
        String str = "你好啊 字节流";
        byte[] b = str.getBytes();
        out.write(b);
        out.close();
    }

 

一个字节一个字节的写入FileOutputStream

@Test
    public void test11() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        OutputStream out = new FileOutputStream(f);
        String str = "nihao 我一个一个字节的写入";
        byte[] b = str.getBytes();
        for (int i = 0; i < b.length; i++) {
            out.write(b[i]);
        }
        out.close();
    }

 

 字节流，向文件中追加新的内容 true FileOutputStream

 @Test
    public void test12() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        OutputStream out = new FileOutputStream(f, true);
        String str = "append Roolen";
        String str2 = "\r\n换行";
        byte[] b1 = str.getBytes();
        byte[] b2 = str2.getBytes();

        for (int i = 0; i < b1.length; i++) {
            out.write(b1[i]);
        }
        for (int i = 0; i < b2.length; i++) {
            out.write(b2[i]);
        }
        out.close();
    }

关于\r\n https://www.cnblogs.com/thinkingthigh/p/7642680.html

Windows系统里面，每行结尾是“<回车><换行>”，即“\r\n”；

 

字节流  读取文件内容FileInputStream

 @Test
    public void test13() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        InputStream in = new FileInputStream(f);
        byte[] b = new byte[1024];
        int len = in.read(b);
        in.close();
        System.out.println(new String(b));
        System.out.println(len);
    }

1024字节，1024byte，

1kb

1byte= 8bit

关于位，字节，字，

 https://blog.csdn.net/m0_37526672/article/details/80273098 

 

 

和上面的对比 主要是(new String(b,0,len));FileInputStream

* 这个emm     什么读取出来会有大量空格，。， 反正拿到的长度是一样的

 @Test
    public void test14() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        InputStream in = new FileInputStream(f);
        byte[] b = new byte[1024];
        int len = in.read(b);
        in.close();
        System.out.println("读入长度为:" + len);
        System.out.println(new String(b, 0, len));
    }

这个我也没去查，就是new String(b,0,len)

 

 

节省空间，，，是不是真的节省了？？FileInputStream

@Test
    public void test15() throws IOException {
        String fileName = "D:" + File.separator + "Hello.txt";
        File f = new File(fileName);
        InputStream in = new FileInputStream(f);
        byte[] b = new byte[(int) f.length()];
        in.read(b);
        System.out.println("文件长度为:" + f.length());
        in.close();
        System.out.println(new String(b));
        System.out.println(b.length);
    }

将上面的改为一个一个读，FileInputStream，对比一个一个写

@Test
    public void test16() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
        InputStream in = new FileInputStream(f);
        byte[] b = new byte[(int) f.length()];
        for (int i = 0; i < b.length; i++) {
            b[i] = (byte) in.read();
        }
        in.close();
        System.out.println(new String(b));
    }

 

 这个说明了，文件读完的时候会返回-1　　FileInputStream

 @Test
    public void test17() throws IOException {
        File f = new File(new String("D:" + File.separator + "hello.txt"));
        InputStream in = new FileInputStream(f);
        byte[] b = new byte[1024];
        int count = 0;
        int temp = 0;
        while ((temp = in.read()) != -1) {
            b[count++] = (byte) temp;
        }
        in.close();
        System.out.println(new String(b));
    }

 

使用字符流,  字符的拼接 FileWriter   总是file--write--output，这就是程序，相对文件的命名方法，这个程序是向文件write，output，往文件写东西，额程序这个时候是
信息输出的

@Test
    public void test18() throws IOException {
        String fileName = "D:" + File.separator + "hello.txt";
        File f = new File(fileName);
//        Writer out = new FileWriter(f);
//        String str = "hello";
        Writer out = new FileWriter(f, true);
        String str = "append\r\nhello";

        out.write(str);
        out.close();
    }

而源码jdk8中

public FileWriter(File file, boolean append) throws IOException {
    super(new FileOutputStream(file, append));
}
实际上就是掉这个fileoutputstream

字符流
* 从字符串中读取内容  FileReader   ---------fileinputstream

 @Test
    public void test19() throws IOException {
        File f = new File(new String("D:" + File.separator + "hello.txt"));
        char[] ch = new char[100];
        Reader reader = new FileReader(f);
        int count = reader.read(ch);
        reader.close();
        System.out.println(count);
        System.out.println(new String(ch, 0, count));
    }

 

 

这么傻逼的循环，你前面这个char还不是设置的有大小的，文件大了还不是废了

 @Test
    public void test20() throws IOException {
        File f = new File(new String("D:" + File.separator + "hello.txt"));
        char[] ch = new char[10];
        Reader reader = new FileReader(f);
        int temp = 0;
        int count = 0;
        while ((temp = reader.read()) != -1) {
            ch[count++] = (char) temp;
        }
        reader.close();
        System.out.println(new String(ch, 0, count));
    }