Java IO流 续

编程技术  /  houtizong 发布于 3年前   81

1.基于字节文件读写

  • FileInputStream和FileOutputStream分别继承自InputStream和OutputStream用于向文件中输入和输出字节。
  • FileInputStream和FileOutputStream的常用构造方法：
    FileInputStream(String name) throws FileNotFoundException
    FileInputStream(File file)   throws FileNotFoundException
    FileOutputStream(String name)throws FileNotFoundException
    FileOutputStream(File file)  throws FileNotFoundException
    FileOutputStream(File file, boolean append)throws FileNotFoundException
  • 注意：
    在实例化FileInputStream和FileOutputSteam流时要用try－catch语句以处理其可能抛出的FileNotFoundException。
    在读写数据时也要用try－catch语句以处理可能抛出的 IOException。
    FileNotFoundException是IOException的子类
  • 读
package javaio.inputstream;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;/** * 将TestFileInputStream.java中的内容读出来 * @author Administrator * */public class TestFileInputStream {public static void main(String[] args) {FileInputStream in = null;try {in = new FileInputStream("D:\\TestFileInputStream.java");} catch (FileNotFoundException e) {System.out.println("没有找到TestFileInputStream.java文件");e.printStackTrace();return;}//如果流不为空循环流if(in!=null){StringBuffer buffer = new StringBuffer();byte b[] = new byte[1024];try {while (in.read(b)!=-1) {buffer.append(new String(b));b = new byte[1024];}System.out.println(buffer.toString());} catch (IOException e) {System.out.println("读取错误");e.printStackTrace();return;//关闭流}finally{if(in!=null){try {in.close();in = null;} catch (IOException e) {e.printStackTrace();}}}}}}
  •  写
package javaio.outputstream;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;/** * 将TestFileInputStream.java中的内容读出来然后写入到TestFileInputStream2.java *  * @author Administrator *  */public class TestFileOutputStream {public static void main(String[] args) {FileInputStream in = null;FileOutputStream out = null;try {in = new FileInputStream("D:\\TestFileInputStream.java");out = new FileOutputStream("D:\\TestFileInputStream2.java");if(in!=null){StringBuffer buffer = new StringBuffer();byte b[] = new byte[1];while (in.read(b)!=-1) {buffer.append(new String(b));out.write(b);b = new byte[1];}}} catch (FileNotFoundException e) {System.out.println("没有找到TestFileInputStream.java文件");e.printStackTrace();return;} catch (IOException e) {System.out.println("读取或写入发生错误");e.printStackTrace();}finally {  try {  if(in != null) {  in.close();   in = null;  }    } catch(IOException e) {    e.printStackTrace();    }  try {  if(out != null) {  out.flush();    out.close();    out = null;    }     } catch(IOException e) {    e.printStackTrace();    }  }}}

 2.基于字符文件读写

  • FileReader 和 FileWriter 分别继承自Reader和Writer，FileInputSteam与FileOutputStream类似，所不同的是FileReader和FileWriter向文件输入和输出的数据单位为字符。
  • FileReader和FileWriter的常用构造方法：
    public FileWriter(File file) throws IOException
    public FileWriter(File file, boolean append)throws IOException
    public FileWriter(String fileName)throws IOException
    public FileWriter(String fileName,boolean append)throws IOException
    public FileReader(String fileName)throws FileNotFoundException
    public FileReader(File file) throws FileNotFoundException
  • 读
package javaio.reader;import java.io.FileNotFoundException;import java.io.FileReader;import java.io.IOException;/** * 读取指定文件内容 *  * @author Administrator *  */public class TestFileReader {public static void main(String[] args) {FileReader reader = null;try {reader = new FileReader("D:\\TestFileReader.java");if(reader!=null){StringBuffer buffer = new StringBuffer();char b[] = new char[1024];while (reader.read(b)!=-1) {buffer.append(new String(b));b = new char[1024];}System.out.println(buffer.toString());}} catch (FileNotFoundException e) {System.out.println("没有找到TestFileReader.java文件");e.printStackTrace();} catch (IOException e) {e.printStackTrace();}finally {if(reader != null) {try{reader.close();}catch (IOException e){e.printStackTrace();}reader = null;}}}}

 

  • 写
package javaio.writer;import java.io.FileNotFoundException;import java.io.FileReader;import java.io.FileWriter;import java.io.IOException;/** * 将TestFileReader.java内容写入到TestFileReader2.java中 * @author Administrator * */public class TestFileWriter {public static void main(String[] args) {FileReader reader = null;FileWriter writer = null;try {reader = new FileReader("D:\\TestFileReader.java");writer = new FileWriter("D:\\TestFileReader2.java");if(reader!=null){char b[] = new char[1];while (reader.read(b)!=-1) {writer.write(b);}}} catch (FileNotFoundException e) {System.out.println("没有找到TestFileReader.java文件");e.printStackTrace();} catch (IOException e) {e.printStackTrace();}finally {if(reader != null) {try{reader.close();}catch (IOException e){e.printStackTrace();}reader = null;}if(writer != null) {try{writer.flush();writer.close();}catch (IOException e){e.printStackTrace();}writer = null;}}}}

 

3.什么时候使用字节流？什么时候使用字符流？

  • 任何数据存在硬盘上时，都是以二进制的形式存储的。
  • 通过使用字节流，可以读取任意文件。字节流一次读取一个字节，而字符流使用了字节流读到一个或者多个字节时，去查找指定的编码表，返回对应的编码。所以字符流只能处理纯文本字符数据，而字节流可以处理更多类型的数据，比如图片，视频，音频文件等。
  • 只要是纯文本数据处理，优先考虑使用字符流。其他情况就使用字节流。

4.缓冲流

  • 缓冲流-Buffered:缓冲流要“套接”在相应的节点流之上，对读写的数据提供了缓冲的功能，提高了读写的效率
  • 读写
    BufferedReader提供了readLine方法用于读取一行字符串（以\r或\n分隔）。
    BufferedWriter提供了newLine用于写入一个行分隔符。
    对于输出的缓冲流，写出的数据会先在内存中缓存，使用flush方法将会使内存中的数据立刻写出。
  • 常用的构造方法
    BufferedReader(Reader in)
    BufferedReader(Reader in,int size) //size 为自定义缓存区的大小
    BufferedWriter(Writer out)
    BufferedWriter(Writer out,int sz)
    BufferedInputStream(InputStream in)
    BufferedInputStream(InputStream in,int size)
    BufferedOutputStream(OutputStream out)
    BufferedOutputStream(OutputStream out,int size)
  • 基于字节读
package javaio.buffered;import java.io.BufferedInputStream;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;/** * 使用缓冲流读取指定文件内容 * @author Administrator * */public class TestBufferedInputStream {  public static void main(String[] args) {  BufferedInputStream bis = null;    try {      InputStream fis =  new FileInputStream("D:\\TestFileInputStream.java");      bis = new BufferedInputStream(fis);      if(bis!=null){StringBuffer buffer = new StringBuffer();byte b[] = new byte[1024];while (bis.read(b)!=-1) {buffer.append(new String(b));b = new byte[1024];}System.out.println(buffer.toString());      }      System.out.println();          } catch (IOException e) {    e.printStackTrace();    } finally {     try {     if(bis != null) {     bis.close();     bis = null;     }    } catch (IOException e) {    e.printStackTrace();    }    }  }}
  •  基于字节写
package javaio.buffered;import java.io.BufferedInputStream;import java.io.BufferedOutputStream;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;/** * 使用缓冲流读取指定文件内容复制到另一个文件 * @author Administrator * */public class TestBufferedOutputStream {public static void main(String[] args) {BufferedInputStream bis = null;BufferedOutputStream bos = null;try {InputStream fis = new FileInputStream("D:\\TestFileInputStream.java");OutputStream out = new FileOutputStream("D:\\TestFileInputStream3.java");bis = new BufferedInputStream(fis);bos = new BufferedOutputStream(out);if (bis != null) {StringBuffer buffer = new StringBuffer();byte b[] = new byte[1];while (bis.read(b) != -1) {buffer.append(new String(b));bos.write(b);b = new byte[1];}}} catch (IOException e) {e.printStackTrace();} finally {try {if (bis != null) {bis.close();bis = null;}if (bos != null) {bos.flush();bos.close();bos = null;}} catch (IOException e) {e.printStackTrace();}}}}
  •  基于字符读写
package javaio.buffered;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.FileNotFoundException;import java.io.FileReader;import java.io.FileWriter;import java.io.IOException;import java.io.Reader;import java.io.Writer;/** * 从指定文件中用BufferedReader读取数据然后用BufferedWriter写入另一个文件中 *  * @author Administrator *  */public class TestBufferedReaderAndWriter {public static void main(String[] args) {BufferedReader breader = null;BufferedWriter bwriter = null;try {Reader reader = new FileReader("D:\\TestFileReader.java");Writer writer = new FileWriter("D:\\TestFileReader3.java");breader = new BufferedReader(reader);bwriter = new BufferedWriter(writer);if(breader!=null){while(breader.ready()){bwriter.write(breader.readLine());bwriter.newLine();}}} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}finally{if(bwriter!=null){try {bwriter.flush();bwriter.close();bwriter = null;} catch (IOException e) {e.printStackTrace();}}if(breader!=null){try {breader.close();breader = null;} catch (IOException e) {e.printStackTrace();}}}}}

 5.转换流

  • InputStreamReader和OutputStreamWriter用与字节数据到字符数据之间的转换。
  • InputStreamReader需要和InputStream “套接”。
  • OutpStreamWriter需要和OutputStream “套接”。
  • 转换流在构造时可以指定其编码集合，例如：
     InputStream isr = new InputStreamReader(InputStream in, CharsetDecoder dec)
  • TestOutputStreamWriter

 

package javaio.transfer;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStreamWriter;/** * 将字节流转换为字符流输出 *  * @author Administrator *  */public class TestOutputStreamWriter {public static void main(String[] args) {OutputStreamWriter osw = null;try {osw = new OutputStreamWriter(new FileOutputStream("D:\\test.txt"),"gbk");osw.write("测试OutputStreamWriter");osw.write("\r\n");osw.write("测试OutputStreamWriter");osw.flush();osw.close();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}}
  •  TestInputStreamReader
package javaio.transfer;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.FileWriter;import java.io.IOException;import java.io.InputStreamReader;/** * 在控制台写入内容保存到文件中 * @author Administrator * */public class TestInputStreamReader {public static void main(String args[]) {InputStreamReader isr = new InputStreamReader(System.in);BufferedReader br = new BufferedReader(isr);BufferedWriter writer = null;try {String str = br.readLine();writer = new BufferedWriter(new FileWriter("D:\\write.txt"));while (str != null) {if ("".equals(str)){break;}writer.write(str);writer.newLine();str = br.readLine();}} catch (IOException e) {e.printStackTrace();}finally{if(br!=null){try {br.close();br=null;} catch (IOException e) {e.printStackTrace();}}if(writer!=null){try {writer.flush();writer.close();writer=null;} catch (IOException e) {e.printStackTrace();}}}}}

6.数据流

  • DataInputStream和DataOutputStream分别继承自InputSteam和OutputStream，它属于过滤流，需要分别“套接”在InputStream 和OutputStream类型的节点流上。
  • DataInputStream和DataOutputStream提供了可以存取与机器无关的Java原始类型数据（如：int，double等）的方法。
  • DataInputStream和DataOutputStream的构造方法为:
    DataInputStream(InputStream in)
    DataOutputStream(OutputStream out)
  • TestDataStream
package javaio.datastream;import java.io.DataInputStream;import java.io.DataOutputStream;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;public class TestDataStream {public static void main(String[] args) {DataOutputStream dos = null;DataInputStream dis = null;try {dos = new DataOutputStream(new FileOutputStream("d:\\data.txt"));dos.writeInt(5);dos.writeDouble(2.12);dos.flush();dos.close();dis = new DataInputStream(new FileInputStream("d:\\data.txt"));System.out.println(dis.readInt());System.out.println(dis.readDouble());dis.close();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}}

7.Print流

  • PrintWriter和PrintStream都属于输出流，分别针对与字符和字节。
  • PrintWriter和PrintStream提供了重载的print
  • println方法用于多种数据类型的输出。
  • PrintWriter和PrintStream有自动flush功能。
package javaio.print;import java.io.FileOutputStream;import java.io.IOException;import java.io.PrintStream;public class TestPrint {public static void main(String[] args) {PrintStream ps = null;try {FileOutputStream fos = new FileOutputStream("D:\\TestFileReader3.java");ps = new PrintStream(fos);} catch (IOException e) {e.printStackTrace();}if (ps != null) {System.setOut(ps);}System.out.println("我们是中国人");System.out.println("我们是中国人");if(ps!=null){ps.flush();ps.close();}}}

 

8.Object流

  • 直接将Object写入或读出
  • transient声明的部分不会被序列化
  • Serializable接口:序列化
  • Externalizable 接口
    void writeExternal(ObjectOutput out) throws IOException
    void readExternal(ObjectInput in) throws IOException,ClassNotFoundException
package javaio.object;import java.io.Serializable;public class Person implements Serializable{private static final long serialVersionUID = 1L;private String name;private String sex;private transient int age = 20;public String getName() {return name;}public String getSex() {return sex;}public int getAge() {return age;}public void setName(String name) {this.name = name;}public void setSex(String sex) {this.sex = sex;}public void setAge(int age) {this.age = age;}}

 

 

package javaio.object;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;public class TestObjectIO {public static void main(String args[]) throws Exception {Person person = new Person();person.setAge(23);person.setName("张三");person.setSex("男");FileOutputStream fos = new FileOutputStream("D://object.data");ObjectOutputStream oos = new ObjectOutputStream(fos);oos.writeObject(person);oos.flush();oos.close();FileInputStream fis = new FileInputStream("D://object.data");ObjectInputStream ois = new ObjectInputStream(fis);Person tReaded = (Person)ois.readObject();System.out.println(tReaded.getName() + " " + tReaded.getSex() + " " + tReaded.getAge());}}

 

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