復(fù)習(xí)
我們用下面一段代碼來(lái)復(fù)習(xí)一下昨天學(xué)的內(nèi)容
File dir = new File("E:\\Workspace\\IdeaStudio\\io-demo\\random-access-file\\demo");
if (!dir.exists()) {
dir.mkdir();
}
if (!dir.isDirectory()) {
System.out.println("新建目錄出錯(cuò)");
}
File file = new File(dir, "file.dat");
if (!file.exists()) {
boolean rs1 = file.createNewFile();
if (!rs1) {
System.out.println("創(chuàng)建文件失敗");
}
}
if (!file.isFile()) {
System.out.println("新建文件出錯(cuò)");
}
我們從構(gòu)成方法開(kāi)始
API
RandomAccessFile(File file, String mode)
創(chuàng)建一個(gè)隨機(jī)訪問(wèn)文件流從File參數(shù)指定的文件中讀取，并可選地寫(xiě)入文件。
RandomAccessFile(String name, String mode)
創(chuàng)建隨機(jī)訪問(wèn)文件流，以從中指定名稱(chēng)的文件讀取，并可選擇寫(xiě)入文件。
我們關(guān)心一下這個(gè)參數(shù) mode：
Value Meaning "r" Open for reading only. Invoking any of the write methods of the resulting object will cause an IOException to be thrown. "rw" Open for reading and writing. If the file does not already exist then an attempt will be made to create it. "rws" Open for reading and writing, as with "rw", and also require that every update to the file's content or metadata be written synchronously to the underlying storage device. "rwd" Open for reading and writing, as with "rw", and also require that every update to the file's content be written synchronously to the underlying storage device.
大概是說(shuō)有四種模式："r"（只讀）、"rw"（讀寫(xiě)）、"rwd"、"rws"。
于是：
String mode = "rw";
RandomAccessFile randomAccessFile = new RandomAccessFile(file, mode);
寫(xiě)點(diǎn)東西
API
void write(int b)
將指定的字節(jié)寫(xiě)入此文件。
詳細(xì)看一下：
public void write(int b)
throws IOException將指定的字節(jié)寫(xiě)入此文件。 寫(xiě)入從當(dāng)前文件指針開(kāi)始。
Specified by:
write在界面 DataOutput
參數(shù)
b - byte 。
異常
IOException - 如果發(fā)生I / O錯(cuò)誤。
這里最重要的亮點(diǎn)：
1、參數(shù)：寫(xiě)進(jìn)去一次一個(gè)字節(jié)（bye 8位）
2、指針
那怎么樣把一個(gè)整數(shù)寫(xiě)進(jìn)去呢？
int b = 0x7fffffff;
randomAccessFile.write(b >>> 24);
randomAccessFile.write(b >>> 16);
randomAccessFile.write(b >>> 8);
randomAccessFile.write(b);
System.out.println(randomAccessFile.getFilePointer());
測(cè)試結(jié)果：
0
4
Process finished with exit code 0
讀一下
API
int read()
從該文件讀取一個(gè)字節(jié)的數(shù)據(jù)。
int read(byte[] b)
從該文件讀取最多 b.length字節(jié)的數(shù)據(jù)到字節(jié)數(shù)組。
byte[] c = new byte[(int)randomAccessFile.length()];
randomAccessFile.read(c);
System.out.println(Arrays.toString(c));
項(xiàng)目經(jīng)驗(yàn)
之前在寫(xiě)一個(gè)物聯(lián)網(wǎng)網(wǎng)關(guān)短信平臺(tái)的時(shí)候，數(shù)據(jù)傳輸就用到byte，那時(shí)候就需要對(duì)這一塊熟悉，還好，網(wǎng)上參考資料比較多，復(fù)制粘貼下來(lái)，也能解決。我們來(lái)看一下：
public final void writeInt(int v) throws IOException {
write((v >>> 24) & 0xFF);
write((v >>> 16) & 0xFF);
write((v >>> 8) & 0xFF);
write((v >>> 0) & 0xFF);
//written += 4;
}
public final void writeLong(long v) throws IOException {
write((int)(v >>> 56) & 0xFF);
write((int)(v >>> 48) & 0xFF);
write((int)(v >>> 40) & 0xFF);
write((int)(v >>> 32) & 0xFF);
write((int)(v >>> 24) & 0xFF);
write((int)(v >>> 16) & 0xFF);
write((int)(v >>> 8) & 0xFF);
write((int)(v >>> 0) & 0xFF);
//written += 8;
}
public final void writeChars(String s) throws IOException {
int clen = s.length();
int blen = 2*clen;
byte[] b = new byte[blen];
char[] c = new char[clen];
s.getChars(0, clen, c, 0);
for (int i = 0, j = 0; i < clen; i++) {
b[j++] = (byte)(c[i] >>> 8);
b[j++] = (byte)(c[i] >>> 0);
}
writeBytes(b, 0, blen);
}
如果你在寫(xiě)項(xiàng)目的時(shí)候，有去看過(guò)大佬封裝的Util，以上這些代碼很眼熟吧，當(dāng)然這些也是jdk大神提供給我們的。
編碼
短信傳輸?shù)木幋a是 UCS2 ，這對(duì)中文來(lái)說(shuō)無(wú)疑是要亂碼的，那怎么辦呢？
如果你也遇到這個(gè)問(wèn)題，我相信你是痛苦的。
當(dāng)時(shí)搜索了大量資料，請(qǐng)教了很多人，當(dāng)然也有代碼。解決方案是：直接轉(zhuǎn)成 UTF-16BE。
這是什么編碼，聽(tīng)都沒(méi)聽(tīng)過(guò)。
Java是雙字節(jié)編碼，就是UTF-16BE。
String s2 = "中";
randomAccessFile.writeChars(s2);
System.out.println(randomAccessFile.getFilePointer());
randomAccessFile.seek(0);
// 寫(xiě)進(jìn)去了嗎，讀一下
byte[] c = new byte[(int)randomAccessFile.length()];
randomAccessFile.read(c);
System.out.println(Arrays.toString(c));
String s1 = new String(c, "utf-16be");
System.out.println(s1);
randomAccessFile.close();
0
2
[78, 45]
中
Process finished with exit code 0
另外，文件都是byte。
資料
1、本節(jié)測(cè)試代碼：random-access-file
