Buffer flow exercise

1、 Use IO Stream encrypts and decrypts pictures

public class PicTest {
    // Image encryption ： XOR the picture 
    @Test
    public void test(){
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream("bird.png");
            fos = new FileOutputStream("bird-secret.png");
            byte[] buffer = new byte[20];
            int len;
            while((len = fis.read(buffer))!=-1){
                // Modify the byte array 
                for(int i=0;i<len; i++){
                    buffer[i] = (byte) (buffer[i] ^ 5);
                }
                fos.write(buffer,0,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fos!=null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fis!=null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    // Picture decryption ： XOR operation of XOR on pictures 
    @Test
    public void test01(){
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream("bird-secret.png");
            fos = new FileOutputStream("bird4.png");
            byte[] buffer = new byte[20];
            int len;
            while((len = fis.read(buffer))!=-1){
                // Modify the byte array 
                for(int i=0;i<len; i++){
                    buffer[i] = (byte) (buffer[i] ^ 5);
                }
                fos.write(buffer,0,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fos!=null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fis!=null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

The encrypted picture cannot be opened

2、 Calculate the number of characters in the text file , And output the results to a text file

/* 1、 Traverse every character of the text 
 * 2、 Number of occurrences of word exists Map in 
 * Map<Character,Integer> map = new HashMap<Character,Integer>();
 * map.put('a',18)
 * map.put(' you ‘,2)
 * 3、 take map The data in is written to a file 
 * /
public class WordCount {
    @Test
    public void testWordCount(){
        FileReader fr = null;
        BufferedWriter bw = null;
        try {
            //1、 establish Map aggregate 
            Map<Character,Integer> map = new HashMap<>();

            //2、 Traverse every character , The number of occurrences of each character map in 
            fr = new FileReader("Hello.txt");
            int c = 0;
            while((c= fr.read())!=-1){
                //int  Restore char
                char ch = (char) c;
                // Judge char Whether in map For the first time 
                if(map.get(ch)==null){
                    map.put(ch,1);
                }else {
                    map.put(ch,map.get(ch)+1);
                }
            }
            //3、 hold map The data in exists in the file count.txt
            //3.1、 establish Writer
            bw = new BufferedWriter(new FileWriter("helloCount.txt"));
            //3.2、 Traverse map, Write data again 
            Set<Map.Entry<Character,Integer>> entrySet = map.entrySet();
            for(Map.Entry<Character,Integer> entry : entrySet){
                switch (entry.getKey()){
                    case ' ':
                        bw.write(" Space ="+entry.getValue());
                        break;
                    case '\t':
                        bw.write("tab key ="+entry.getValue());
                        break;
                    case '\r':
                        bw.write(" enter ="+entry.getValue());
                        break;
                    case '\n':
                        bw.write(" Line break ="+entry.getValue());
                        break;
                    default:
                        bw.write(entry.getKey()+"="+entry.getValue());
                }
                bw.newLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(bw!=null){
                try {
                    bw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fr!=null){
                try {
                    fr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}