Java操作手册：IO流总结（第6篇）
小海洋why
本节重点讲解Java中的IO流，Java中所有字节相关的输入流的基类为InputStream、输出流的基类为OutputStream，Java中所有与字符相关的输入流的基类为Reader、输出流的基类为Writer。如果操作的是字符，可以选择用字符流和字节流，如果操作的是非字符，只能用字节流。常见字符流包括：（FileReader，FileWriter）、（BufferedReader，BufferedWriter），常见的字节流包括（FileInputStream，FileOutputStream）、（BufferedInputStream，BufferedOutputStream），常见转换流包括InputStreamReader、OutputStreamWriter，Java也提供了常用的文件封装类File。下面一一介绍。
一、字符流
FileReader：读取字符文件，具体例子如下。
public static void main(String[] args) {
FileReader reader = null;
try {
reader = new FileReader("D:/why.txt");
int len = 0;
char[] buf = new char[1024];
while((len = reader.read(buf)) != -1) {
System.out.println(new String(buf, 0, len));
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
BufferedReader：提供字符流读取时的缓冲区，减少IO操作，提高读取效率。具体例子如下。
public static void main(String[] args) {
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader("D:/why.txt"));
int len = 0;
char[] buf = new char[1024];
while((len = reader.read(buf)) != -1) {
System.out.println(new String(buf, 0, len));
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
FileReader和BufferedReader用时对比试验，注意，选择大文件效果才明显
public static void main(String[] args) {
fileReader();
bufferedReader();
}
private static void bufferedReader() {
long starTime = System.currentTimeMillis();
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader("D:/why.txt"));
int len = 0;
char[] buf = new char[1024];
while((len = reader.read(buf)) != -1) {
System.out.println(new String(buf, 0, len));
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("BufferedReader用时："+(endTime - starTime)+"毫秒");
}
private static void fileReader() {
long starTime = System.currentTimeMillis();
FileReader reader = null;
try {
reader = new FileReader("D:/why.txt");
int len = 0;
char[] buf = new char[1024];
while((len = reader.read(buf)) != -1) {
System.out.println(new String(buf, 0, len));
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("FileReader用时："+(endTime - starTime)+"毫秒");
}
FileWriter：写文件，具体例子如下。
long starTime = System.currentTimeMillis();
FileWriter writer = null;
try {
writer = new FileWriter("D:/why.txt");
writer.write("dsss");
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (writer != null) {
writer.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("+=用时："+(endTime - starTime)+"毫秒");
}
BufferedWriter：写文件，具体例子如下。
public static void main(String[] args) {
long starTime = System.currentTimeMillis();
BufferedWriter writer = null;
try {
writer = new BufferedWriter(new FileWriter("D:/why.txt"));
writer.write("dsss");
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if (writer != null) {
writer.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("+=用时："+(endTime - starTime)+"毫秒");
}
二、字节流
FileInputStream：以字节流方式读文件，具体例子如下。
public static void main(String[] args) {
long starTime = System.currentTimeMillis();
FileInputStream fis = null;
try {
fis = new FileInputStream("D:/why.txt");
int len = 0;
byte[] buf = new byte[1024];
while((len = fis.read(buf)) != -1) {
System.out.println(new String(buf, 0, len));
}
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if (fis != null) {
fis.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("+=用时："+(endTime - starTime)+"毫秒");
}
BufferedInputStream：以带缓冲区的字节流方式读，与FileInputStream的对比试验可自行参照上面例子编写。具体例子如下。
public static void main(String[] args) {
long starTime = System.currentTimeMillis();
BufferedInputStream bis = null;
try {
bis = new BufferedInputStream(new FileInputStream("D:/why.txt"));
int len = 0;
byte[] buf = new byte[1024];
while((len = bis.read(buf)) != -1) {
System.out.println(new String(buf, 0, len));
}
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if (bis != null) {
bis.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("+=用时："+(endTime - starTime)+"毫秒");
}
FileOutputStream：以字节流方式写，具体例子如下。
public static void main(String[] args) {
long starTime = System.currentTimeMillis();
FileOutputStream fos = null;
try {
fos = new FileOutputStream("D:/why.txt");
fos.write("dsss".getBytes());
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if (fos != null) {
fos.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("+=用时："+(endTime - starTime)+"毫秒");
}
BufferedOutputStream：以带缓冲区的字节流方式写，具体例子如下。
public static void main(String[] args) {
long starTime = System.currentTimeMillis();
BufferedOutputStream bos = null;
try {
bos = new BufferedOutputStream(new FileOutputStream("D:/why.txt"));
bos.write("dsss".getBytes());
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if (bos != null) {
bos.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
long endTime = System.currentTimeMillis();
System.out.println("+=用时："+(endTime - starTime)+"毫秒");
}
三、转换流
当我们读取字符数据时，使用字符流效率比字节流高，因此有时需要将字节流转换为字符流。
将字节输入流转换为字符输入流
BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream("D:/why.txt")));
将字节输出流转换为字符输出流
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("D:/why.txt")));
四、File类
为了描述文件，Java提供File类，使用方法如下。
File file = new File("D:/why.txt");
File类为我们提供了很多关于文件的信息，比如文件大小、文件名等，方便我们操作。我们可将上述程序中的"D:/why.txt"替换为new File("D:/why.txt");，读者可在IDE中尝试。
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