Java文件实例

文件创建

File createTempFile(String prefix, String suffix,File directory) prefix文件名 suffix文件后缀 directory 文件目录

File file = null;
        File dir = new File("C:\\Users\\MACHENIKE\\Desktop");
        file = File.createTempFile
                ("createText", ".txt", dir);
        System.out.println(file.getPath());

源码 分析可知当文件名长度小于3时会抛出异常

public static File createTempFile(String prefix, String suffix,
                                      File directory)
        throws IOException
    {
        if (prefix.length() < 3)
            throw new IllegalArgumentException("Prefix string too short");
        if (suffix == null)
            suffix = ".tmp";

        File tmpdir = (directory != null) ? directory
                                          : TempDirectory.location();
        SecurityManager sm = System.getSecurityManager();
        File f;
        do {
            f = TempDirectory.generateFile(prefix, suffix, tmpdir);

            if (sm != null) {
                try {
                    sm.checkWrite(f.getPath());
                } catch (SecurityException se) {
                    // don't reveal temporary directory location
                    if (directory == null)
                        throw new SecurityException("Unable to create temporary file");
                    throw se;
                }
            }
        } while ((fs.getBooleanAttributes(f) & FileSystem.BA_EXISTS) != 0);

        if (!fs.createFileExclusively(f.getPath()))
            throw new IOException("Unable to create temporary file");

        return f;
    }

文件写入实例

在路径下有create.txt文件则修改，没有就创建

    @Test
    public void file() throws IOException {
        BufferedWriter out = new BufferedWriter(new FileWriter("C:\\Users\\MACHENIKE\\Desktop\\create.txt"));
        out.write("hello word");
        out.close();
        System.out.println("文件创建成功！");
    }

读取文件内容

BufferedReader in = new BufferedReader(new FileReader("C:\\Users\\MACHENIKE\\Desktop\\createText.txt"));
        String str;
while ((str = in.readLine()) != null) {
            System.out.println(json);
        }

上面读取文件可能会乱码，需要在读取的时候转换成相应的编码

//一、转换成byte数组
BufferedReader in = new BufferedReader(new FileReader("C:\\Users\\MACHENIKE\\Desktop\\createText.txt"));
        String str;
        while ((str = in.readLine()) != null) {
            byte[] bytes = str.getBytes();
            String json = new String(bytes, "UTF-8");
            System.out.println(json);
        }
//二、读取时候设置编码
BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream("C:\\Users\\MACHENIKE\\Desktop\\createText.txt"),"UTF-8"));
        String str;
        while ((str = in.readLine()) != null) {
            System.out.println(str);
        }

删除文件

File file = new File("C:\\Users\\MACHENIKE\\Desktop\\createText.txt");
        if(file.delete()){
            System.out.println(file.getName() + " 删除成功！");
        }else{
            System.out.println("删除失败！");
        }

检测文件是否存在

File file = new File("C:\\Users\\MACHENIKE\\Desktop\\nonentity.txt");
        System.out.println(file.exists());

修改文件名称

File oldName = new File("C:\\Users\\MACHENIKE\\Desktop\\createText.txt");//旧文件
        File newName = new File("C:\\Users\\MACHENIKE\\Desktop\\newText.txt");//新文件
        if (oldName.renameTo(newName)){
            System.out.println("成功");
        } else {
            System.out.println("失败");
        }

获取文件大小

File file = new File("C:\\Users\\MACHENIKE\\Desktop\\newText.txt");
        if (!file.exists() || !file.isFile()) {
            System.out.println("文件不存在");
        }
        System.out.println(file.length());//单位字节

设置文件只读

File file = new File("C:\\Users\\MACHENIKE\\Desktop\\newText.txt");
        System.out.println(file.setReadOnly());
        //该方法返回true，如果应用程序写入文件，否则该方法返回false。
        System.out.println(file.canWrite());