概念:
外觀模式(Facade),爲一套繁雜的子系統中的一組接口提供一個一致的界面,定義一個高層接口,這個接口使得這一子系統更加容易使用。其應用場景
1.爲一個複雜子系統提供一個簡單接口。
2.提高子系統的獨立性,降低耦合度
3.在層次化結構中,可以使用Facade模式定義系統中每一層的入口。
例子:
將基目錄下source文件中的字串讀取出,然後md5加密,再將加密的結果,輸出到目標文件
類圖:
FileRead class:
public class FileRead {
private static String TAG = "FileRead";
public String read(String fileName) {
StringBuilder stringBuilder = new StringBuilder();
File psicacheFile = new File(fileName);
if (!psicacheFile.exists()) {
Log.d(TAG, String.format("File:%s does not exists!",fileName));
} else {
try {
FileReader fr = new FileReader(fileName);
BufferedReader br = new BufferedReader(fr);
String s = br.readLine();
while (s != null) {
stringBuilder.append(s);
s = br.readLine();
}
br.close();
fr.close();
} catch (IOException ioe) {
Log.v(TAG, ioe.toString());
}
}
Log.d(TAG, String.format("FileRead String: %s", stringBuilder));
return stringBuilder.toString();
}
}
Encryptor加密類:
public class Encryptor {
public final String MD5(String s) {
char hexDigits[] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
try {
byte[] btInput = s.getBytes();
MessageDigest mdInst = MessageDigest.getInstance("MD5");
// 使用指定的字節更新摘要
mdInst.update(btInput);
// 獲得密文
byte[] md = mdInst.digest();
// 把密文轉換成十六進制的字符串形式
int j = md.length;
char str[] = new char[j * 2];
int k = 0;
for (int i = 0; i < j; i++) {
byte byte0 = md[i];
str[k++] = hexDigits[byte0 >>> 4 & 0xf];
str[k++] = hexDigits[byte0 & 0xf];
}
return new String(str);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
}
FileWrite class:
public class FileWrite {
private static String TAG = "FileWrite";
public void write(String fileName,String string){
File psicacheFile = new File(fileName);
if (!psicacheFile.exists()) {
Log.d(TAG, String.format("File:%s does not exists!",fileName));
try {
psicacheFile.createNewFile();
Log.d(TAG, String.format("File:%s create done!",fileName));
} catch (IOException ioe) {
Log.v(TAG, ioe.toString());
}
}
if (psicacheFile.exists()) {
try {
FileWriter fw = new FileWriter(fileName);
BufferedWriter writer = new BufferedWriter(fw);
writer.write(string);
writer.close();
fw.close();
Log.d(TAG, String.format("File:%s write in %s",fileName,string));
} catch (IOException ioe) {
Log.v(TAG, ioe.toString());
}
}
}
}
Encryptable
public interface Encryptable {
public void encrypt(String sourcefile, String outfile);
}
EncryptFacade外觀類:
public class EncryptFacade implements Encryptable {
private FileRead fileRead;
private Encryptor encryptor;
private FileWrite fileWrite;
@Override
public void encrypt(String sourcefile, String outfile) {
if (null != fileRead && null != encryptor && null != fileWrite) {
fileWrite.write(outfile, encryptor.MD5(fileRead.read(sourcefile)));
}
}
public EncryptFacade() {
fileRead = new FileRead();
encryptor = new Encryptor();
fileWrite = new FileWrite();
}
}
測試類
public class WorkClass {
public void test() {
Encryptable encryptFacade= new EncryptFacade();
encryptFacade.encrypt("/sdcard/source.txt","/sdcard/out.txt"); }}
測試結果:
14:56:18.155 23149-23149/com.example.qinghua_liu.myapplication D/FileRead: FileRead String:facade design14:56:18.155 23149-23149/com.example.qinghua_liu.myapplication D/Encryptor: Encryptor MD5 facade design to 696A9711DC2670D3293E98087F94CACE
14:56:18.157 23149-23149/com.example.qinghua_liu.myapplication D/FileWrite: File:/sdcard/out.txt does not exists!
14:56:18.159 23149-23149/com.example.qinghua_liu.myapplication D/FileWrite: File:/sdcard/out.txt create done!
14:56:18.162 23149-23149/com.example.qinghua_liu.myapplication D/FileWrite: File:/sdcard/out.txt write in 696A9711DC2670D3293E98087F94CACE
結語:
外觀模式是爲了解決子系統中類與類之間的依賴關係的,像spring一樣,可以將類和類之間的關係配置到配置文件中,而外觀模式就是將他們的關係放在一個Facade類中,降低了類類之間的耦合度。如果我們沒有EncryptFacade類,那麼,FileRead、FileWrite、Encryptor他們之間將會相互持有實例,產生關係,這樣會造成嚴重的依賴,修改一個類,可能會帶來其他類的修改,這不是我們想要看到的,有了EncryptFacade類,他們之間的關係被放在了EncryptFacade類裏,這樣就起到了解耦的作用,這也是外觀模式的意義。