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IO流
1 概述
1). IO流基礎知識
[1]. IO的用途:IO流是用來處理設備之間的數據傳輸的
[2]. 早期的Java的IO包中都是字節流(體現均爲二進制字節)
[3]. 字符流是從字節流中分離出來的,用來處理文本數據的流。
2). IO流的抽象基類
[1]. 字節流的抽象基類 ---- InputStream和OutputStream
[2]. 字符流的抽象基類 ---- Reader和Writer
2 字符流
字符流繼承體系結構 (Reader和Writer)
字符流寫入
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
public class Demo {
public static void main(String[] args ) {
//創建要操作的文件路徑和名稱
//其中,File.separator表示系統相關的分隔符,Linux下爲:/ Windows下爲:\\
String path = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "demo.txt";
//由於IO操作會拋出異常,因此在try語句塊的外部定義FileWriter的引用
FileWriter w = null;
try {
//以path爲路徑創建一個新的FileWriter對象
//如果需要追加數據,而不是覆蓋,則使用FileWriter(path,true)構造方法
w = new FileWriter(path);
//將字符串寫入到流中,\r\n表示換行想有好的
w.write("Nerxious is a good boy\r\n");
//如果想馬上看到寫入效果,則需要調用w.flush()方法
w.flush();
} catch (IOException e) {
e.printStackTrace();
} finally {
//如果前面發生異常,那麼是無法產生w對象的
//因此要做出判斷,以免發生空指針異常
if(w != null) {
try {
//關閉流資源,需要再次捕捉異常
w.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
字符流讀取
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
public class Demo2 {
public static void main(String[] args ) {
String path = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "demo.txt";
FileReader r = null;
try {
r = new FileReader(path);
//方式一:讀取單個字符的方式
//每讀取一次,向下移動一個字符單位
int temp1 = r.read();
System.out.println((char)temp1);
int temp2 = r.read();
System.out.println((char)temp2);
//方式二:循環讀取
//read()方法讀到文件末尾會返回-1
/*
while (true) {
int temp = r.read();
if (temp == -1) {
break;
}
System.out.print((char)temp);
}
*/
//方式三:循環讀取的簡化操作
//單個字符讀取,當temp不等於-1的時候打印字符
/*int temp = 0;
while ((temp = r.read()) != -1) {
System.out.print((char)temp);
}
*/
//方式四:讀入到字符數組
/*
char[] buf = new char[1024];
int temp = r.read(buf);
//將數組轉化爲字符串打印,後面參數的意思是
//如果字符數組未滿,轉化成字符串打印後尾部也許會出現其他字符
//因此,讀取的字符有多少個,就轉化多少爲字符串
System.out.println(new String(buf,0,temp));
*/
//方式五:讀入到字符數組的優化
//由於有時候文件太大,無法確定需要定義的數組大小
//因此一般定義數組長度爲1024,採用循環的方式讀入
/*
char[] buf = new char[1024];
int temp = 0;
while((temp = r.read(buf)) != -1) {
System.out.print(new String(buf,0,temp));
}
*/
} catch (IOException e) {
e.printStackTrace();
} finally {
if(r != null) {
try {
r.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
文本文件的複製
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class Demo {
public static void main(String[] args ) {
String doc = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "demo.txt";
String copy = File.separator + "home" + File.separator + "siu" +
File.separator + "life" + File.separator + "lrc.txt";
FileReader r = null;
FileWriter w = null;
try {
r = new FileReader(doc);
w = new FileWriter(copy);
//方式一:單個字符寫入
int temp = 0;
while((temp = r.read()) != -1) {
w.write(temp);
}
//方式二:字符數組方式寫入
/*
char[] buf = new char[1024];
int temp = 0;
while ((temp = r.read(buf)) != -1) {
w.write(new String(buf,0,temp));
}
*/
} catch (IOException e) {
e.printStackTrace();
} finally {
//分別判斷是否空指針引用,然後關閉流
if(r != null) {
try {
r.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(w != null) {
try {
w.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
字符串緩衝流對文本文件複製
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class Demo {
public static void main(String[] args ) {
String doc = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "demo.txt";
String copy = File.separator + "home" + File.separator + "siu" +
File.separator + "life" + File.separator + "lrc.txt";
FileReader r = null;
FileWriter w = null;
//創建緩衝區的引用
BufferedReader br = null;
BufferedWriter bw = null;
try {
r = new FileReader(doc);
w = new FileWriter(copy);
//創建緩衝區對象
//將需要提高效率的FileReader和FileWriter對象放入其構造函數內
//當然,也可以使用匿名對象的方式 br = new BufferedReader(new FileReader(doc));
br = new BufferedReader(r);
bw = new BufferedWriter(w);
String line = null;
//讀取行,直到返回null
//readLine()方法只返回換行符之前的數據
while((line = br.readLine()) != null) {
//使用BufferWriter對象的寫入方法
bw.write(line);
//寫完文件內容之後換行
//newLine()方法依據平臺而定
//windows下的換行是\r\n
//Linux下則是\n
bw.newLine();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
//此處不再需要捕捉FileReader和FileWriter對象的異常
//關閉緩衝區就是關閉緩衝區中的流對象
if(br != null) {
try {
r.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(bw != null) {
try {
bw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
3 字節流
字節流繼承體系結構 (InputStream和OutputStream)
字節流寫入
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
public class Demo {
public static void main(String[] args ) {
String path = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "demo.txt";
FileOutputStream o = null;
try {
o = new FileOutputStream(path);
String str = "Nerxious is a good boy\r\n";
byte[] buf = str.getBytes();
//也可以直接使用o.write("String".getBytes());
//因爲字符串就是一個對象,能直接調用方法
o.write(buf);
} catch (IOException e) {
e.printStackTrace();
} finally {
if(o != null) {
try {
o.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
字節流讀取
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
public class Demo {
public static void main(String[] args ) {
String path = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "demo.txt";
FileInputStream i = null;
try {
i = new FileInputStream(path);
//方式一:單個字符讀取
//需要注意的是,此處我用英文文本測試效果良好
//但中文就悲劇了,不過下面兩個方法效果良好
int ch = 0;
while((ch=i.read()) != -1){
System.out.print((char)ch);
}
//方式二:數組循環讀取
/*
byte[] buf = new byte[1024];
int len = 0;
while((len = i.read(buf)) != -1) {
System.out.println(new String(buf,0,len));
}
*/
//方式三:標準大小的數組讀取
/*
//定一個一個剛好大小的數組
//available()方法返回文件的字節數
//但是,如果文件過大,內存溢出,那就悲劇了
//所以,親們要慎用!!!上面那個方法就不錯
byte[] buf = new byte[i.available()];
i.read(buf);
//因爲數組大小剛好,所以轉換爲字符串時無需在構造函數中設置起始點
System.out.println(new String(buf));
*/
} catch (IOException e) {
e.printStackTrace();
} finally {
if(i != null) {
try {
i.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
mp3格式文件用字節數組複製
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class Demo {
public static void main(String[] args ) {
String bin = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "一個人生活.mp3";
String copy = File.separator + "home" + File.separator + "siu" +
File.separator + "life" + File.separator + "一個人生活.mp3";
FileInputStream i = null;
FileOutputStream o = null;
try {
i = new FileInputStream(bin);
o = new FileOutputStream(copy);
//循環的方式讀入寫出文件,從而完成複製
byte[] buf = new byte[1024];
int temp = 0;
while((temp = i.read(buf)) != -1) {
o.write(buf, 0, temp);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if(i != null) {
try {
i.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(o != null) {
try {
o.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
mp3格式文件用字符串緩衝區複製
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class Demo {
public static void main(String[] args ) {
String bin = File.separator + "home" + File.separator + "siu" +
File.separator + "work" + File.separator + "一個人生活.mp3";
String copy = File.separator + "home" + File.separator + "siu" +
File.separator + "life" + File.separator + "一個人生活.mp3";
FileInputStream i = null;
FileOutputStream o = null;
BufferedInputStream bi = null;
BufferedOutputStream bo = null;
try {
i = new FileInputStream(bin);
o = new FileOutputStream(copy);
bi = new BufferedInputStream(i);
bo = new BufferedOutputStream(o);
byte[] buf = new byte[1024];
int temp = 0;
while((temp = bi.read(buf)) != -1) {
bo.write(buf,0,temp);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if(bi != null) {
try {
i.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(bo != null) {
try {
o.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
------ android培訓、java培訓、java學習型技術博客、期待與您交流! ----------