RandomAccessFile
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構造方法
//var1 文件路徑,var 文件的讀寫模式 "r"只讀，"w"只寫，"rw"讀寫 public RandomAccessFile(String var1, String var2) throws FileNotFoundException { this(var1 != null?new File(var1):null, var2); } //傳文件，和模式 public RandomAccessFile(File var1, String var2) throws FileNotFoundException { } -
其他常用方法
public void close () 關閉操作 public int read ( byte[] b)將內容讀取到一個byte數組之中 public final byte readByte () 讀取一個字節 public final int readInt () 從文件中讀取整型數據。 public void seek ( long pos)設置讀指針的位置。 public final void writeBytes (String s)將一個字符串寫入到文件之中，按字節的方式處理。 public final void writeInt ( int v)將一個int型數據寫入文件，長度為4位。 public int skipBytes ( int n)指針跳過多少個字節。
RandomAccessFile 讀寫案例
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文件路徑
//文件路徑 public static final String PATH = "/Volumes/huang/studyfromGitHub/JavaForAndroid/JavaForAndroid/series11/src/main/java/files/testRAF.txt"; -
寫
/** * */ private static void testWrite() { RandomAccessFile accessFile = null; try { //讀寫模式創建實例 accessFile = new RandomAccessFile(PATH, "rw"); //讀取文件長度 System.out.println(accessFile.length() + " B");//0B //將文件指針移動中間位置 accessFile.seek(accessFile.length() / 2); String name = null; int age = 0;// int 的長度為4 float money = 1.2f;// float 的長度為4 //double長度為8 name = "name1";// 長度為5de字符串 age = 20; money = 23.5f; accessFile.writeBytes(name); //讀取文件長度 System.out.println(accessFile.length() + "B");//5B accessFile.writeInt(age); System.out.println(accessFile.length() + "B");//9B accessFile.writeFloat(money); System.out.println(accessFile.length() + "B");//13B System.out.println("================================"); name = "name2";// 長度為5de字符串 age = 21; money = 24.5f; accessFile.writeBytes(name); System.out.println(accessFile.length() + "B");//18B accessFile.writeInt(age); System.out.println(accessFile.length() + "B");//22B accessFile.writeFloat(money); System.out.println(accessFile.length() + "B");//26B //accessFile.writeUTF("hello，你好！"); //注：從中間寫入的數據是覆蓋后面的內容，因此在寫數據時，盡量追加在內容之后 } catch (Exception e) { e.printStackTrace(); } finally { try { accessFile.close(); } catch (IOException e) { e.printStackTrace(); } } } -
讀
/** * 讀 */ private static void testRead() { RandomAccessFile accessFile = null; //讀寫模式創建實例 try { accessFile = new RandomAccessFile(PATH, "r");//只讀模式創建實例 String name = null; int age = 0; float money = 0.0f; byte[] bytes = new byte[5]; //假如要先讀第二個人的信息 accessFile.skipBytes(13);//則跳過前13字節 for (int i = 0; i < bytes.length; i++) { bytes[i] = accessFile.readByte();//讀取一個字節 } name = new String(bytes); age = accessFile.readInt(); money = accessFile.readFloat(); System.out.println("name2:-->" + name + "\t" + age + "\t" + money); //讀第一個 accessFile.seek(0);//指針回到0 //假如要先讀第二個人的信息 for (int i = 0; i < bytes.length; i++) { bytes[i] = accessFile.readByte();//讀取一個字節 } name = new String(bytes); age = accessFile.readInt(); money = accessFile.readFloat(); System.out.println("name1:-->" + name + "\t" + age + "\t" + money); } catch (Exception e) { e.printStackTrace(); }finally { try { accessFile.close(); } catch (IOException e) { e.printStackTrace(); } } } -
讀的運行結果
DataOutputStream(數據輸出流)、DataInputStream(數據輸入流)
DataOutputStream
構造方法
//傳入一個字節輸出流
public DataOutputStream(OutputStream var1) {
super(var1);
}
用法案例
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文件路徑
public static final String PATH = "/Volumes/huang/studyfromGitHub/JavaForAndroid/JavaForAndroid/series11/src/main/java/files/testOutput.txt"; -
寫
/** * DataOutputStream 寫 */ private static void write() { DataOutputStream outputStream = null; try { //傳入字節流實例獲取對象實例 outputStream = new DataOutputStream(new FileOutputStream(PATH)); //寫入基本數據 outputStream.writeUTF("你好，Java"); //寫入utf-8編碼字符串 outputStream.writeInt(10); outputStream.writeInt(34); outputStream.writeChar('a'); outputStream.writeBoolean(true); } catch (Exception e) { e.printStackTrace(); }finally { try { outputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } -
讀
/** * */ private static void read() { DataInputStream inputStream=null; try { inputStream=new DataInputStream(new FileInputStream(PATH)); //2. 讀取數據 String txt=inputStream.readUTF();//讀取utf-8編碼的字符串 int a=inputStream.readInt(); int b=inputStream.readInt(); int num=inputStream.readChar(); boolean flag=inputStream.readBoolean(); System.out.println(txt+"\r\n"+a+" "+b+","+num+","+flag); } catch (Exception e) { e.printStackTrace(); }finally { //關閉流 try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } -
讀結果
ByteArrayInputStream、ByteArrayOutputStream很常用的兩個類
ByteArrayInputStream
構造方法
//使用一個字節數組當中所有的數據做為數據源
public ByteArrayInputStream(byte[] var1) {
.....
}
//從數組當中的第offset開始，一直取出length個這個字節做為數據源。
public ByteArrayInputStream(byte[] var1, int var2, int var3) {
....
}
ByteArrayOutputStream
構造方法
//創建一個32個字節的緩沖區
public ByteArrayOutputStream() {
this(32);
}
//根據參數指定大小創建緩沖區
public ByteArrayOutputStream(int var1) {
if(var1 < 0) {
throw new IllegalArgumentException("Negative initial size: " + var1);
} else {
this.buf = new byte[var1];
}
}
這兩個構造函數創建的緩沖區大小在數據過多的時候都會自動增長。
案例運用
/**
* ByteArrayOutputStream拷貝本文件內容
*/
public class Demo9 {
//源文件路徑
public static final String sourcePath = "/Volumes/huang/studyfromGitHub/JavaForAndroid/JavaForAndroid/series11/src/main/java/com/example/Demo9.java";
public static void main(String[] args) {
try {
//得到字節流
FileInputStream inputStream = new FileInputStream(sourcePath);
//將字節流轉成字符流
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
//將字節流包裝成一個緩沖字符流
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
//創建內存流對象--內存輸出流
ByteArrayOutputStream arrayOutputStream = new ByteArrayOutputStream(inputStream.available());
//將字節流轉換成字符流
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(arrayOutputStream);
//將字符流包裝成緩沖字符流--BufferedWriter
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
String msg = null;
while ((msg = bufferedReader.readLine()) != null) {
bufferedWriter.write(msg);//向內存中寫入數據
bufferedWriter.newLine();
bufferedWriter.flush();//將緩沖區的數據寫入到內存流中使用的內存區中
}
byte[] bytes = arrayOutputStream.toByteArray();
System.out.println(new String(bytes));
//關閉流
bufferedReader.close();
bufferedWriter.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}