Buffered stream, the stream conversion

1. buffered stream

1. Definitions

Buffered stream, the stream is high, is an enhancement to the four basic FileXxx stream, so the flow is four

Byte stream buffer: BufferedInputStream, BufferedOutputStream
Character buffer stream: BufferedReader, BufferedWriter

The basic principle of the buffer stream, it is to create objects, creates a built-in default size of the buffer array, reading and writing through the buffer zone to reduce the number of system io

2. byte stream buffer

Construction method

public BufferedInputStream(InputStream in): Create a new buffered stream object
public BufferedOutputStream(OutputStream out): Create a new buffered stream object

For example construction

// 创建字节缓冲输入流
BufferedInputStream bis = new BufferedInputStream(new FileInputStream("a.txt")); // 创建字节缓冲输出流 BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("b.txt"));

Use case realization stream buffer

public class BufferedDemo{
  public static void main(String[] args){ // 记录开始时间 long start = System.currentTimeMillis(); // 创建流对象 try( BufferedInputStream bis = new BufferedInputStream(new FileInputStream("jdk.exe")); BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("copy.exe")); ){ //读写数据 int b; while((b=bis.read())!=-1){ bos.write(b); }catch(IOException e){ e.printStackTrace(); } // 记录结束的时间 long end = System.currentTImeMillis(); System.out.println("索要时间为"+(end-start)+"毫秒"); } } }

Using arrays, speed

public class BufferedDemo{
  public static void main(String[] args){ // 记录开始时间 long start = System.currentTimeMillis(); // 创建流对象 try( BufferedInputStream bis = new BufferedInputStream(new FileInputStream("jdk.exe")); BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("copy.exe")); ){ //读写数据 int len; byte[] bytes = new byte[8*1024]; while((len=bis.read())!=-1){ bos.write(bytes, 0, len); }catch(IOException e){ e.printStackTrace(); } // 记录结束的时间 long end = System.currentTImeMillis(); System.out.println("索要时间为"+(end-start)+"毫秒"); } } }

3. character buffer flow

Construction method

public BufferedReader(Reader in): Create a new buffered input stream
public BufferedWriter(Writer out): Creates a new buffered output stream

For example construction

// 创建字符缓冲输入流
BufferedReader br = new BufferedReader(new FileReader("br.txt")); // 创建字符缓冲输出流 BufferedWriter bw = new BufferedWriter(new FileWriter("bw.txt"));

Unique method

The basic method is consistent character buffer stream and the general stream of characters is called

BufferedReader: public String readLine(): Read a line of text
BuffferedWriter: public void newLine(): Writing a line line separator, there are system-defined symbol

readLineWay to demonstrate

public class BufferedReaderDemo{
  public static void main(String[] args) throws IOException{ //创建流对象 BufferedReader br = new BufferedReader(new FileReader("in.txt")); //定义字符串,保存读取的一行文字 String line = null; //循环读取,读到最后返回null while((line=br.read())!=null){ System.out.println(line); System.out.println("-----"); } //释放资源 br.close(); } }

newLineWay to demonstrate

public class BufferedWriterDemo{
  public static void main(String[] args) throws IOException{ // 创建流对象 BufferedWriter bw = new BufferedWriter(new FileWriter("bw.txt")); //写出数据 bw.write("黑马"); bw.newLine(); bw.write("程序"); bw.newLine(); //释放资源 bw.close(); } }

2. Conversion flow

1. `IuputStreamReader`class

Commutations java.io/InputStreamReaderis Readera child class of bytes to read, using the specified character set and decodes it into a character.

Construction method

InputStreamReader(InputStream in): Create one using the default character set of character stream
InputStreamReader(InputStream in, String charsetName): Create a character set specified character stream

For example construction

InputStreamReader isr = new InputStreamReader(new FileInputStream("in.txt"));
InputStreamReader isr = new InputStreamReader(new FileInputStream("in.txt"), "GBK");

Specifies the code reading

public class ReaderDemo{
  public static void main(String[] args) throws IOException{ // 定义文件位置, 文件为gbk编码 String FileName = "E:\\file_txt"; // 创建流对象指定为GBK InputStreamReader isr = new InputStreamReader(new FileInputStream(FileName), "GBK"); //定义变量, 保存字符 int read; //循环读取 while((read=isr.read())!=-1){ System.out.println((char) read); } //关闭资源 isr.close(); } }

2. `OutputStreamWrite`class

It is Writesubclass

Construction method

OutputStreamWriter(OutputStream in): Create one using the default character set of character stream
OutputStreamWriter(OutputStream in, String chasetName): Create a character set specified character stream

Configuration examples

OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("a.txt"));
OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("a.txt"), "GBK");

Specify the encoding write

public class OutputDemo{
  public static void main(String[] args) throws IOException{ //定义文件路径 String FileName = "E:\\out.txt"; //创建流对象 OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream(FileName), "GBK"); osw.write("你好"); osw.close(); } }

3. Serialization

Provides for a Java object serialization mechanisms, an object can be represented by a sequence of bytes, the byte containing the sequence , and other information. After a sequence of bytes written to the file, the file corresponding to the information stored in a persistent object. 对象的数据 对象的类型 对象中存储的属性

Conversely, the byte sequence can also be read from a file back, rearranged, it is deserialized. 对象的数据 , 对象的类型 And the 对象中存储的数据information can be used to create objects in memory.

1.ObjectOutputStream类

Construction method

public ObjectOutputStream(OutputStream out): A wear member designated the OutputStream ObjectOutputStream

Configuration examples

FileOutputStream FileOut = new FileOutputStream("a.txt");
ObjectOutputStream out = new ObjectOutputStream(FileOut);

Sequence of Operation

1. An object serialization order, two conditions must be met

This class is the java.io.Serializableinterface Serializableis a marker interface does not implement this interface will not use any state serialization and de-serialization throwsNotSerializableException
All the attributes of the class must be serialized, if there is a property not to be serialized, then change the property must be marked transient, using the transientkeyword modifications

public class Employle implements java.io.Serializable{ public String name; public String address; public transient int age; //tanisent瞬态修饰成员, 不会被序列化 }

2. Write Object Methods

public final void writeObject(Object obj): The development of object write

public class Serializable{
  public static void main(String[] args){ Employee e = new Employee(); e.name = "张三"; e.address = "北大"; e.age = 20; try{ //创建序列化流对象 ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("a.txt")); //写出对象 out.writeObject(e); //释放资源 out.close(); Fileout.close(); System.out.println("Serializable 打他 is saved") }catch(IOException i){ i.printStackTrace(); } } }

2. `ObjectInputStream`class

Construction method

public ObjectInputStream(InputStream in): A wear member designated the InputStream ObjectInputStream.

1 deserialization

If you can find a class file object, we can deserialize

public final Object readObject(): Reads an object

public class DeserialixeDemo{
  public static void main(String[] args){ Employee e = null; try{ //创建反序列化流 FileInputStream fileIn = new FileInputStream("a.txt"); ObjectInputStream in = new ObjectInputStream(FileIn); //读取一个对象 e = (Employee) in .readObject(); //释放资源 in.close(); fileIn.close(); }catch(IOException i){ //捕获异常 i.printStackTrace(); return; }catch(ClassNotFoundException c){ // 捕获找不到异常 System.out.println("not found"); c.printStrackTrace(); return; } // 无异常,直接打印输出 System.out.println(e.name); System.out.println(e.address); System.out.println(e.age); } }

Deserialize 2

In addition, when the JVM deserialize objects to find class files, but the class files have changed after a serialized object, then the deserialization operation

As also fails, throw a InvalidClassException exception. This exception occurs for the following reasons:

Such serial version number of the version number of the class descriptor read from the stream does not match
This class contains unknown data type
No parameters such constructions are not accessible method

Serializable interface to require serialization class that provides a serial version number. SerialVersionUID purpose is to verify the version number and the corresponding sequence of the target classes whether to match the version

public class Employee implements java.io.Serializable{ //加入序列版本号 private static final long serialVersionUID = 1L; public String name; public String address; //添加新的属性,重新编译 public int eid; public void adressCheck(){ System.out.println("adress check"+name+"--"+adress); } }

4. Print stream

Usually we use the console to print, print和printlnfrom the java.io.PrintStreamclass

1.PrintStream class

Construction method

public PrintStream(String FileName): Specified file name to create a new print stream

Configuration examples

PrintStream ps = new PrintStream("ps.txt");

Change the flow of print

System.outIt is the PrintStreamtype of

public class PrintDemo{
  public static void main(String[] args) throws IOException{ //调用系统的打印流 System.out.println(97); //创建打印流,指定文件的名称 PrintStream ps = new PrintStream("ps.txt"); // 设置系统的流向到ps.txt中 System.setOut(ps); //调用打印的方法, ps.txt中输出97 System.out.println(97); } }