最近的项目需要将Android上的内容以文件的形式保存到硬盘.基础数据类型比较容易序列化,但是一些不可以实现Serializable ,或者Parcelable接口的系统类,如何实例化?例如系统的Bitmap
- 最开始的时候使用的ObjectOutputStream的形式保存的.只需要在实体类中写入readObject和writeObject方法就可以.ObjectOutputStream会在序列化的时候通过反射调用这两个方法进行序列化和反序列化.但是该方法有一个缺陷,就是当实体类新增字段的时候,以前保存的反序列化的时候将会失败.
- 后来考虑使用json的形式保存.下面介绍一下简单的实现.
- 需要的第三方库如下.
//谷歌的Gson
implementation 'com.google.code.gson:gson:2.8.5'
//GitHub上一个比较好的工具类集合utilcode
implementation 'com.blankj:utilcode:1.20.4'
实体类
public class Person {
public String name;
public int age;
public Bitmap bitmap;
public String bitmap2String;
/**
* 序列化的时候调用该方法
*/
public void serializer() {
if (bitmap != null) {
//将不可序列化的bitmap转为可以序列化的字符串,通过base64进行压缩
byte[] bytes = BitmapUtils.getBytes(bitmap, Bitmap.CompressFormat.JPEG);
this.bitmap2String = Base64Util.encode(bytes);
}
}
/**
* 反序列化的时候调用该方法
*/
public void deserializer() {
if (bitmap2String != null) {
//通过base64进行解码,将以字符串保存的bitmap 解码
byte[] bytes = Base64Util.decode(bitmap2String);
this.bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
}
}
}
序列化的方法
Person person = new Person();
person.bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher_foreground);
person.name = "老王";
person.age = 23;
peoples.add(person);
person.serializer();
Gson gson = new Gson();
String s = gson.toJson(peoples);
反序列化的方法
Person person = gson.fromJson(stringPersons, Person.class);
person.deserializer();
imageView.setImageBitmap(person.bitmap);
textView.setText(person.name);
将序列化之后的String保存到储存卡
File path = Environment.getExternalStorageDirectory();
String filePath = path + "/person.txt";
final File file = new File(filePath);
try {
FileOutputStream fileOutputStream = new FileOutputStream(file);
fileOutputStream.write(s.getBytes());
fileOutputStream.flush();
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
读取已经保存的序列化之后的文件
StringBuilder stringBuilder = new StringBuilder();
FileInputStream fileInputStream = new FileInputStream(file);
String line = "";
BufferedReader reader = new BufferedReader(new InputStreamReader(fileInputStream));
line = reader.readLine();
while (line != null) {
stringBuilder.append(line);
stringBuilder.append("\n");
line = reader.readLine();
}
reader.close();
fileInputStream.close();
String person = stringBuilder.toString();
实体类中使用到的Base64Util
public class Base64Util {
private static final char[] ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
.toCharArray();
private static final char last2byte = (char) Integer
.parseInt("00000011", 2);
private static final char last4byte = (char) Integer
.parseInt("00001111", 2);
private static final char last6byte = (char) Integer
.parseInt("00111111", 2);
private static final char lead6byte = (char) Integer
.parseInt("11111100", 2);
private static final char lead4byte = (char) Integer
.parseInt("11110000", 2);
private static final char lead2byte = (char) Integer
.parseInt("11000000", 2);
private static final char[] encodeTable = new char[] { 'A', 'B', 'C', 'D',
'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q',
'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q',
'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3',
'4', '5', '6', '7', '8', '9', '+', '/' };
private static int[] toInt = new int[128];
static {
for (int i = 0; i < ALPHABET.length; i++) {
toInt[ALPHABET[i]] = i;
}
}
/**
* Base64 encoding.
*
* @param from
* The src data.
* @return cryto_str
*/
public static String encode(byte[] from) {
StringBuilder to = new StringBuilder((int) (from.length * 1.34) + 3);
int num = 0;
char currentByte = 0;
for (int i = 0; i < from.length; i++) {
num = num % 8;
while (num < 8) {
switch (num) {
case 0:
currentByte = (char) (from[i] & lead6byte);
currentByte = (char) (currentByte >>> 2);
break;
case 2:
currentByte = (char) (from[i] & last6byte);
break;
case 4:
currentByte = (char) (from[i] & last4byte);
currentByte = (char) (currentByte << 2);
if ((i + 1) < from.length) {
currentByte |= (from[i + 1] & lead2byte) >>> 6;
}
break;
case 6:
currentByte = (char) (from[i] & last2byte);
currentByte = (char) (currentByte << 4);
if ((i + 1) < from.length) {
currentByte |= (from[i + 1] & lead4byte) >>> 4;
}
break;
default:
break;
}
to.append(encodeTable[currentByte]);
num += 6;
}
}
if (to.length() % 4 != 0) {
for (int i = 4 - to.length() % 4; i > 0; i--) {
to.append("=");
}
}
return to.toString();
}
/**
* Translates the specified Base64 string into a byte array.
*
* @param s the Base64 string (not null)
* @return the byte array (not null)
*/
public static byte[] decode(String s) {
int delta = s.endsWith( "==" ) ? 2 : s.endsWith( "=" ) ? 1 : 0;
byte[] buffer = new byte[s.length() * 3 / 4 - delta];
int mask = 0xFF;
int index = 0;
for (int i = 0; i < s.length(); i += 4) {
int c0 = toInt[s.charAt( i )];
int c1 = toInt[s.charAt( i + 1)];
buffer[index++] = (byte)(((c0 << 2) | (c1 >> 4)) & mask);
if (index >= buffer.length) {
return buffer;
}
int c2 = toInt[s.charAt( i + 2)];
buffer[index++] = (byte)(((c1 << 4) | (c2 >> 2)) & mask);
if (index >= buffer.length) {
return buffer;
}
int c3 = toInt[s.charAt( i + 3 )];
buffer[index++] = (byte)(((c2 << 6) | c3) & mask);
}
return buffer;
}
}