RandomAccessFile
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构造方法
//var1 文件路径,var 文件的读写模式 "r"只读，"w"只写，"rw"读写 public RandomAccessFile(String var1, String var2) throws FileNotFoundException { this(var1 != null?new File(var1):null, var2); } //传文件，和模式 public RandomAccessFile(File var1, String var2) throws FileNotFoundException { } -
其他常用方法
public void close () 关闭操作 public int read ( byte[] b)将内容读取到一个byte数组之中 public final byte readByte () 读取一个字节 public final int readInt () 从文件中读取整型数据。 public void seek ( long pos)设置读指针的位置。 public final void writeBytes (String s)将一个字符串写入到文件之中，按字节的方式处理。 public final void writeInt ( int v)将一个int型数据写入文件，长度为4位。 public int skipBytes ( int n)指针跳过多少个字节。
RandomAccessFile 读写案例
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文件路径
//文件路径 public static final String PATH = "/Volumes/huang/studyfromGitHub/JavaForAndroid/JavaForAndroid/series11/src/main/java/files/testRAF.txt"; -
写
/** * */ private static void testWrite() { RandomAccessFile accessFile = null; try { //读写模式创建实例 accessFile = new RandomAccessFile(PATH, "rw"); //读取文件长度 System.out.println(accessFile.length() + " B");//0B //将文件指针移动中间位置 accessFile.seek(accessFile.length() / 2); String name = null; int age = 0;// int 的长度为4 float money = 1.2f;// float 的长度为4 //double长度为8 name = "name1";// 长度为5de字符串 age = 20; money = 23.5f; accessFile.writeBytes(name); //读取文件长度 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";// 长度为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：从中间写入的数据是覆盖后面的内容，因此在写数据时，尽量追加在内容之后 } catch (Exception e) { e.printStackTrace(); } finally { try { accessFile.close(); } catch (IOException e) { e.printStackTrace(); } } } -
读
/** * 读 */ private static void testRead() { RandomAccessFile accessFile = null; //读写模式创建实例 try { accessFile = new RandomAccessFile(PATH, "r");//只读模式创建实例 String name = null; int age = 0; float money = 0.0f; byte[] bytes = new byte[5]; //假如要先读第二个人的信息 accessFile.skipBytes(13);//则跳过前13字节 for (int i = 0; i < bytes.length; i++) { bytes[i] = accessFile.readByte();//读取一个字节 } name = new String(bytes); age = accessFile.readInt(); money = accessFile.readFloat(); System.out.println("name2:-->" + name + "\t" + age + "\t" + money); //读第一个 accessFile.seek(0);//指针回到0 //假如要先读第二个人的信息 for (int i = 0; i < bytes.length; i++) { bytes[i] = accessFile.readByte();//读取一个字节 } 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(); } } } -
读的运行结果
DataOutputStream(数据输出流)、DataInputStream(数据输入流)
DataOutputStream
构造方法
//传入一个字节输出流
public DataOutputStream(OutputStream var1) {
super(var1);
}
用法案例
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文件路径
public static final String PATH = "/Volumes/huang/studyfromGitHub/JavaForAndroid/JavaForAndroid/series11/src/main/java/files/testOutput.txt"; -
写
/** * DataOutputStream 写 */ private static void write() { DataOutputStream outputStream = null; try { //传入字节流实例获取对象实例 outputStream = new DataOutputStream(new FileOutputStream(PATH)); //写入基本数据 outputStream.writeUTF("你好，Java"); //写入utf-8编码字符串 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(); } } } -
读
/** * */ private static void read() { DataInputStream inputStream=null; try { inputStream=new DataInputStream(new FileInputStream(PATH)); //2. 读取数据 String txt=inputStream.readUTF();//读取utf-8编码的字符串 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 { //关闭流 try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } -
读结果
ByteArrayInputStream、ByteArrayOutputStream很常用的两个类
ByteArrayInputStream
构造方法
//使用一个字节数组当中所有的数据做为数据源
public ByteArrayInputStream(byte[] var1) {
.....
}
//从数组当中的第offset开始，一直取出length个这个字节做为数据源。
public ByteArrayInputStream(byte[] var1, int var2, int var3) {
....
}
ByteArrayOutputStream
构造方法
//创建一个32个字节的缓冲区
public ByteArrayOutputStream() {
this(32);
}
//根据参数指定大小创建缓冲区
public ByteArrayOutputStream(int var1) {
if(var1 < 0) {
throw new IllegalArgumentException("Negative initial size: " + var1);
} else {
this.buf = new byte[var1];
}
}
这两个构造函数创建的缓冲区大小在数据过多的时候都会自动增长。
案例运用
/**
* ByteArrayOutputStream拷贝本文件内容
*/
public class Demo9 {
//源文件路径
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 {
//得到字节流
FileInputStream inputStream = new FileInputStream(sourcePath);
//将字节流转成字符流
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
//将字节流包装成一个缓冲字符流
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
//创建内存流对象--内存输出流
ByteArrayOutputStream arrayOutputStream = new ByteArrayOutputStream(inputStream.available());
//将字节流转换成字符流
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(arrayOutputStream);
//将字符流包装成缓冲字符流--BufferedWriter
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
String msg = null;
while ((msg = bufferedReader.readLine()) != null) {
bufferedWriter.write(msg);//向内存中写入数据
bufferedWriter.newLine();
bufferedWriter.flush();//将缓冲区的数据写入到内存流中使用的内存区中
}
byte[] bytes = arrayOutputStream.toByteArray();
System.out.println(new String(bytes));
//关闭流
bufferedReader.close();
bufferedWriter.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}