关于java.io的学习记录(读取文本)
可以通过字节流(FileInputStream)、字符流(InputStreamReader)、字符缓冲流(BufferedReader)读取文本中的数据。
1、FileInputStream读取文本
public void read(){String path = "fileTest.txt";FileInputStream in = null;try {in = new FileInputStream(path);byte[] temp = new byte[10] ;int len;StringBuffer sb = new StringBuffer();// 文件中有中文时会乱码while ((len=in.read(temp))!=-1){String s = new String(temp, 0, len);sb.append(s);System.out.println("--------[-" + String.valueOf(s) + "-]----");}System.out.println();System.out.println(sb.toString());} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {if(in!= null){try {in.close();} catch (IOException e) {e.printStackTrace();}}}}
运行说明:
1)出现乱码(文本是GBK的,程序默认是utf-8)
2)按照设置的字符长度,一段段的输出(据说实际上是一个个字节的读取,效率比较低)
其他:
字节流可以处理所有的数据类型,例如图片、视频、文本
InputStreamReader读取文本
public void read2(){String path = "fileTest.txt";FileInputStream in = null;InputStreamReader inputStreamReader = null;try {in = new FileInputStream(path); // 字节流inputStreamReader = new InputStreamReader(in, "GBK"); // 字符流char[] temp = new char[20];int len;StringBuffer sb = new StringBuffer();while ((len = inputStreamReader.read(temp)) != -1){String s = new String(temp, 0, len);sb.append(s);System.out.println("--------[-" + String.valueOf(s) + "-]----");}System.out.println();System.out.println(sb.toString());} catch (FileNotFoundException e) {e.printStackTrace();} catch (UnsupportedEncodingException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {if(in!= null){try {in.close();} catch (IOException e) {e.printStackTrace();}}if(inputStreamReader != null){try {inputStreamReader.close();} catch (IOException e) {e.printStackTrace();}}}}
运行说明:
1)InputStreamReader可以设置编码格式,读取中文时可以正常显示
2)按照设置的字符长度,一段段的输出(据说实际上是一个个字符的读取)
其他:
字符流只能处理文本数据
BufferedReader读取文本
public void read3(){String path = "fileTest.txt";FileInputStream in = null;InputStreamReader inputStreamReader = null;BufferedReader reader = null;try {in = new FileInputStream(path); // 字节流inputStreamReader = new InputStreamReader(in, "GBK"); // 字符流reader = new BufferedReader(inputStreamReader); // 字符缓冲流StringBuffer sb = new StringBuffer();char[] temp = new char[20];int len;while ((len = reader.read(temp)) != -1){String s = new String(temp, 0, len);sb.append(s);System.out.println("--------[-" + String.valueOf(s) + "-]----");}System.out.println();System.out.println(sb.toString());} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {if(in!= null){try {in.close();} catch (IOException e) {e.printStackTrace();}}if(inputStreamReader != null){try {inputStreamReader.close();} catch (IOException e) {e.printStackTrace();}}if(reader != null){try {reader.close();} catch (IOException e) {e.printStackTrace();}}}}
运行说明:
1)BufferedReader包裹了InputStreamReader,所以中文也能正常显示
2)从打印的结果看,跟InputStreamReader的效果一样(据说BufferedReader更快)
3)reader创建公式
xxInputStream in = ....
InputStreamReader iReader = new InputStreamReader(in);
BufferedReader reader = new BufferedReader(iReader);
BufferedReader读取文本,按行读取
...
StringBuffer sb = new StringBuffer();
String temp;
while ((temp = reader.readLine()) != null){sb.append(temp);System.out.println("--------[-" + temp + "-]----");
}
System.out.println();
System.out.println(sb.toString());
...
运行说明:
1)一行行的读取,读取的数据中不包含\\n、\\r
2)据说没有数据时会断,在数据流异常或者断开时才会返回null
读取文本异常
char[] temp = new char[20];
int len;
StringBuffer sb = new StringBuffer();
while ((len = inputStreamReader.read(temp)) != -1){sb.append(temp);System.out.println("-len=[" + len + "]-[-" + String.valueOf(temp) + "-]----");
}
System.out.println();
System.out.println(sb.toString());
运行说明:
1)最后一次读取的时候,残留了上一次的数据。观看源码,read的时候,是一个个char修改的,当i到16的时候,已经没有数据,则返回结果,此时17到19这三个char没有被处理,所以保存数据的时候,要用new String(temp, 0, len)截取数据