张国敬 Java培训 = 文件读写

src/main/java/com/exercise/fileio/ExerciseFirst.java

+package com.exercise.fileio;
+
+import java.io.File;
+
+/**
+ * 张国敬 Java培训 = 文件读写
+ * 编写一段程序，判断d:/study/io目录是否存在，存在则遍历输出这个目录的所有文件名称，不存在则创建这个目录
+ * @author elliot
+ */
+public class ExerciseFirst {
+    public static void main(String[] args){
+        String target = "/Users/elliot/JavaProjects/java-exercise/src/main/java/com/exercise/fileio/exercise";
+        listFiles(target);
+    }
+
+    public static void listFiles(final String path)
+    {
+        File file = new File(path);
+        if(! file.exists()){
+            System.out.println("该文件不存在，创建该文件");
+            file.mkdirs();
+            return;
+        }
+
+        String[] children = file.list();
+        if(children == null || children.length == 0){
+            return;
+        }
+
+        for (String child : children){
+            String childPath = path + File.separator + child;
+            File childFile = new File(childPath);
+            if(childFile.isFile()){
+                System.out.println("找到了一个文件：" + childPath);
+            }else{
+                listFiles(childPath);
+            }
+        }
+    }
+}

src/main/java/com/exercise/fileio/ExerciseFourth.java

+package com.exercise.fileio;
+
+import java.io.*;
+
+/**
+ * 编写一个文件复制函数，copyFile(String from, String to)，from为原文件名，to为复制后的新文件名，复制结束打印
+ * 所复制的文件大小和用时（毫秒），执行结果如：copy xxx use xxx ms, file size is xxx
+ * @author elliot
+ */
+public class ExerciseFourth {
+    public static void main(String[] args){
+        String fromFile = "/Users/elliot/JavaProjects/java-exercise/src/main/java/com/exercise/fileio/exercise/test.txt";
+        String targetFile = "/Users/elliot/JavaProjects/java-exercise/src/main/java/com/exercise/fileio/exercise/test_copy.txt";
+
+        copyFile(fromFile, targetFile);
+    }
+
+    /**
+     * 复制文件
+     * @param from
+     * @param to
+     * @return
+     */
+    public static void copyFile(String from, String to){
+        long currentTimeMillisStart = System.currentTimeMillis();
+
+        File file = new File(from);
+        if(! file.exists()){
+            System.out.println("文件不存在");
+            return;
+        }
+
+
+        InputStream in = null;
+        OutputStream out = null;
+
+        try {
+            in = new FileInputStream(file);
+            out = new FileOutputStream(new File(to));
+
+            byte[] bytes = new byte[4096];
+
+            int len = 0;
+            while ((len = in.read(bytes)) > 0){
+                out.write(bytes, 0, len);
+            }
+        }catch (IOException e){
+            e.printStackTrace();
+        }finally {
+            if(in != null){
+                try {
+                    in.close();
+                } catch (IOException e) {
+                    e.printStackTrace();
+                }
+            }
+            if(out != null){
+                try {
+                    out.close();
+                } catch (IOException e) {
+                    e.printStackTrace();
+                }
+            }
+        }
+
+        long currentTimeMillisEnd = System.currentTimeMillis();
+
+        System.out.println("copy from " + from + " use " + (currentTimeMillisEnd - currentTimeMillisStart) + "ms, file size is " + file.length());
+
+    }
+}

src/main/java/com/exercise/fileio/ExerciseSecond.java

+package com.exercise.fileio;
+
+import java.io.File;
+
+/**
+ * 编写一段程序，删除d:/study/io这个目录下的大于20Kb的文件
+ * @author elliot
+ */
+public class ExerciseSecond {
+    public static void main(String[] args){
+        String target = "/Users/elliot/JavaProjects/java-exercise/src/main/java/com/exercise/fileio/exercise";
+        listFilesAndClear(target);
+    }
+
+    public static void listFilesAndClear(final String path)
+    {
+        File file = new File(path);
+        if(! file.exists()){
+            return;
+        }
+
+        String[] children = file.list();
+        if(children == null || children.length == 0){
+            return;
+        }
+
+        for (String child : children){
+            String childPath = path + File.separator + child;
+            File childFile = new File(childPath);
+            if(childFile.isFile() && childFile.length() > (20 * 1024)){
+                System.out.println("找到了一个大于20KB的文件并删除：" + childPath);
+                childFile.delete();
+            }else{
+                listFilesAndClear(childPath);
+            }
+        }
+    }
+}

src/main/java/com/exercise/fileio/ExerciseThird.java

+package com.exercise.fileio;
+
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.*;
+
+/**
+ * 编写一段程序，循环从键盘输入一行字符，把这行字符首尾颠倒后按行输出到一个文件中，遇到quit后退出
+ * @author elliot
+ */
+public class ExerciseThird {
+    public static void main(String[] args){
+        System.out.println("请输入一段字符：");
+        Scanner scanner = new Scanner(System.in);
+        String s = scanner.next();
+        System.out.println("输入的字符是：" + s);
+
+        // 把这行字符首尾颠倒
+        String reverseString = stringReverse(s);
+        System.out.println("倒序后的字符是：" + reverseString);
+
+        // 输出到一个文件中
+        String fileName = "/Users/elliot/JavaProjects/java-exercise/src/main/java/com/exercise/fileio/exercise/test.txt";
+        stringWrite(reverseString, fileName);
+
+    }
+
+    /**
+     * 颠倒字符顺序
+     * @param string
+     * @return
+     */
+    public static String stringReverse(String string){
+        String[] s = string.split("");
+        String str = new String();
+        List<String> list = new ArrayList<>(Arrays.asList(s));
+        Collections.reverse(list);
+        for (Object o : list) {
+            str = str + o;
+        }
+        return str;
+    }
+
+
+    /**
+     * 将字符写到文件中
+     * @param str
+     * @param str
+     */
+    public static void stringWrite(String str, String fileName){
+        FileWriter fw = null;
+        try {
+            fw = new FileWriter(fileName);
+            fw.write(str);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }finally{
+            if(fw != null){
+                try {
+                    fw.close();
+                } catch (IOException e) {
+                    e.printStackTrace();
+                }
+            }
+        }
+
+
+    }
+}

src/main/java/com/exercise/fileio/exercise/test.txt

+111111
\ No newline at end of file

src/main/java/com/exercise/fileio/exercise/test_copy.txt

+111111
\ No newline at end of file