IO基础之转换流、内存流和合并流

转换流：把字节流转换成字符流
InputStreamReader：把字节输入流转成字符输入流。
OutputStreamWriter：把字节输出流转成字符输出流。

为什么有字节流转字符流，没有字符流转字节流：

字节流可以操作一切文件（纯文本文件/二进制文件）

字符流用来操作中文纯文本文件使用的，本身是对字节流的增强。

下面实现一下转换：

/**
* Created by Layne_Yao on 2017-7-28 下午2:59:07.
* CSDN:http://blog.csdn.net/Jsagacity
*/
public class StreamTransformReaderDemo {

public static void main(String[] args) throws Exception, FileNotFoundException {
File srcFile = new File("file/stream.txt");
File destFile = new File("target/stream.txt");

//把字节流转换成字符流
Reader in = new InputStreamReader(new FileInputStream(srcFile),"GBK");
Writer out = new OutputStreamWriter(new FileOutputStream(destFile),"GBK");

//接下来操作字符流
char[] buffer = new char[1024];
int len = -1;
while((len = in.read(buffer))!=-1){
out.write(buffer,0,len);
}
in.close();
out.close();

}

}

内存流（数组流）：
把数据先临时存在数组中，待会再从数组中获取出来：

1、字节内存流：ByteArrayOutputStream/ByteArrayInputStream

2、字符内存流：CharArrayWriter/CharArrayReader

3、字符串流：StringWriter/StringReader
字节内存流：

/**
* Created by Layne_Yao on 2017-7-28 下午3:22:45.
* CSDN:http://blog.csdn.net/Jsagacity
*/
//字节的数组流/内存流
public class ByteArrayDemo {

public static void main(String[] args) throws Exception {
//字节数组输出流：程序->内存
ByteArrayOutputStream bos = new ByteArrayOutputStream();
bos.write("ABCDE".getBytes());
//要使用存储的临时数据
byte[] buffer = bos.toByteArray();

//字节数组输入流：内存-->程序
ByteArrayInputStream bis = new ByteArrayInputStream(buffer);
byte[] bys = new byte[5];
int len = -1;
while ((len = bis.read(bys)) != -1) {
System.out.println(new String(bys, 0, len));
}

//其实无需关闭流
bis.close();
bos.close();

}

}

字符内存流：

/**
* Created by Layne_Yao on 2017-7-28 下午3:35:21.
* CSDN:http://blog.csdn.net/Jsagacity
*/
// 字符内存流/数组流
public class CharArrayDemo {

public static void main(String[] args) throws Exception {
// 字符数组输出流
CharArrayWriter writer = new CharArrayWriter();
writer.write("这是字符内存流！！！");
char[] data = writer.toCharArray();

// 字符数组输入流
CharArrayReader reader = new CharArrayReader(data);
char[] bys = new char[10];
int len = -1;
while ((len = reader.read(bys)) != -1) {
System.out.println(new String(bys, 0, len));
}

//其实无需关闭流
writer.close();
reader.close();

}

}

字符串流：

/**
* Created by Layne_Yao on 2017-7-28 下午3:50:24.
* CSDN:http://blog.csdn.net/Jsagacity
*/
//字符串流（字符串的内存流）
public class StringWriterReaderDemo {

public static void main(String[] args) throws Exception {
//字符串的输出流
StringWriter sWriter = new StringWriter();
sWriter.write("字符串流（字符串的内存流）");

//字符串的输入流
StringReader sReader = new StringReader(sWriter.toString());
char[] buffer = new char[1024];
int len = -1;
while((len = sReader.read(buffer))!=-1){
System.out.println(new String(buffer,0,len));
}

//其实无需关闭流
sWriter.close();
sReader.close();
}

}

合并流：

主要的功能是将两个文件的内容合并成一个文件；

下面将两个文件合并在一起：

/**
* Created by Layne_Yao on 2017-7-28 下午3:40:21.
* CSDN:http://blog.csdn.net/Jsagacity
*/
//合并流
public class SequenceDemo {
public static void main(String args[]) throws Exception {
//两个文件的输入流
InputStream is1 = new FileInputStream("file/a.txt");
InputStream is2 = new FileInputStream("file/b.txt");

//文件的输出流
OutputStream os = new FileOutputStream("target/ab.txt");

//将两个输入流合并
SequenceInputStream sis = new SequenceInputStream(is1, is2);

int len = -1;
while ((len = sis.read()) != -1) {
os.write(len);
}
sis.close();
is1.close();
is2.close();
os.close();
}
}