黑马程序员---IO流

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String

StringBuffer  同步安全，效率比之StringBuilder低，可变字符序列
StringBuilder 不同步，效率高，可变字符序列。

String str=”1”+”2”+”3”+”4”;
会分别在字符串池中创建“12””123”  “1234”多出2个不需要的字符串。而StringBuilder与StringBuffer对象通过append(String)添加字符串只会在字符串中创建一个字符串。

IO流

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流向分为：输出流(写入),输入流(读取)  流操作数据分为：字符流，字节流

字符流抽象基类：Reader Writer    字节流抽象基类:InputStream OutputStream

流对象一旦创建，必须close()流。关闭流后，流就不能进行任何操作了。好比男女朋友一样，一旦创建恋爱关系，当不爱时也得说一句分手，得告诉对方咱们不是男女朋友关系了,彼此自由了。但你我就不要再有任何联系了。

字节输入流中的available()判断读取文件的大小

flush()：当输出流使用到缓冲区的时候需要在write()后flush()

//字符输入流

FileReader fileReader=null;
String str="";
BufferedReader bufr=null;
try {
fileReader=new FileReader("abc.txt");
bufr=new BufferedReader(fileReader);

while((str=bufr.readLine())!=null){
System.out.println(str);
}

} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
if (bufr!= null) {
try {
bufr.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

//字符输出流

FileWriter fileWriter = null;
BufferedWriter bufw = null;
String str = "";
try {
fileWriter = new FileWriter("abc.txt");
bufw= new BufferedWriter(fileWriter);

bufw.write("234");
bufw.flush();

} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (bufw != null) {
try {
bufw.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

//复制文件1

private static void copyFile1() throws IOException {
FileInputStream fileInputStream = new FileInputStream("123.mp4");
BufferedInputStream bufInputStream = new BufferedInputStream(
fileInputStream);

FileOutputStream fileOutputStream = new FileOutputStream("321.mp4");
BufferedOutputStream bufOutputStream = new BufferedOutputStream(
fileOutputStream);

//缓冲区中再次使用缓冲区
int len = 0;
byte []by=new byte[1024];
while ((len = bufInputStream.read(by)) != -1) {
bufOutputStream.write(by,0,len);
bufOutputStream.flush();
}
//不在自定义缓冲区了(经过简单测试此比有缓冲区慢)
/*int ch=0;
while ((ch=bufInputStream.read())!=-1) {
bufOutputStream.write(ch);
}*/
bufInputStream.close();
bufOutputStream.close();
}

//复制文件2(自定义缓冲区)

private static void copyFile2() throws IOException {
FileInputStream fileInputStream=new FileInputStream("123.mp4");
FileOutputStream fileOutputStream=new FileOutputStream("321.mp4");

int len=0;
byte[]by=new byte[1024];
while((len=fileInputStream.read(by))!=-1){
fileOutputStream.write(by, 0, len);
fileOutputStream.flush();
}

fileInputStream.close();
fileOutputStream.close();

}

缓冲:BufferedReader (子类 LineNumberReader跟踪行号的缓冲字符输入流) BufferedWriter  BufferedOutputStream BufferedInputStream  装饰设计模式

装饰设计模式

需对某对象的功能进行扩展，可以使用装饰设计模式而非使用继承。因为只对某功能进行扩展，使用继承的话，子类会多出没必要进行扩展的功能会使得整个类体系杂乱臃肿。装饰比继承灵活。装饰类和被装饰类都必须实现同一接口或所属同一父类。

 默认的输入设备和输出设备的流不需要关，因为只有一个流。InputStream in=System.in;in.read();in.close();

转换流：InputStreamReader 字节流转换为字符流 此过程称为解码

                        OutputStreamWriter   字符流转换为字节流  此过程称为编码

//遍历目录

private static void fileList(File file) throws IOException {
if (file.isDirectory()) {
File[] strings = file.listFiles();
for (File string1 : strings) {
if (string1.isDirectory()) {
fileList(string1);
} else {
System.out.println(string1.getName());
}
}
}

}

//删除文件夹及文件

private static void fileList(File file) throws IOException {
if (file.isDirectory()) {
File[] strings = file.listFiles();
for (File string1 : strings) {
/*if (string1.isDirectory()) {
fileList(string1);
} else {
System.out.println(string1.getName());
}*/
if(string1.isDirectory()){
fileList(string1);
}else{
string1.delete();
}
}
file.delete();
}

}

//将properties数据存储到文件中

Properties properties=new Properties();
properties.setProperty("123", "abc");
properties.setProperty("345", "efg");
properties.setProperty("567", "hjk");

OutputStream outputStream=new FileOutputStream("info.txt");

properties.store(outputStream, "");

outputStream.close();

//文件合并

ArrayList<FileInputStream> alArrayList=new ArrayList<FileInputStream>();
alArrayList.add(new FileInputStream("1.txt"));
alArrayList.add(new FileInputStream("2.txt"));
alArrayList.add(new FileInputStream("3.txt"));

Enumeration<FileInputStream> en=Collections.enumeration(alArrayList);

SequenceInputStream sequenceInputStream=new SequenceInputStream(en);

FileOutputStream fileOutputStream=new FileOutputStream("4.txt");
byte []by=new byte[1024];
int len=0;
while((len=sequenceInputStream.read(by))!=-1){
fileOutputStream.write(by,0,len);
}
sequenceInputStream.close();
fileOutputStream.close();

//文件切割

FileInputStream fileInputStream=new FileInputStream("38.mp4");
FileOutputStream fileOutputStream=null;
int len=0;
byte[]by=new byte[1024*1000];//1M
int count=0;
while((len=fileInputStream.read(by))!=-1){
count++;
fileOutputStream=new FileOutputStream(count+".part");
fileOutputStream.write(by,0, len);
}
fileInputStream.close();
fileOutputStream.close();

//文件过滤及删除

File file = new File("E:\\Eclipse\\exam");//此处得是目录，否则异常 得先判断

if(file.isDirectory()){

File[] f = file.listFiles(new MyFileFilter());//此处可以使用内部类避免单独创建一个过滤类
for (File file2 : f) {
System.out.println(file2.toString());
file2.delete();
}

}

//过滤器

public class MyFileFilter implements FilenameFilter {

@Override
public boolean accept(File dir, String name) {
// TODO Auto-generated method stub
return name.endsWith(".part");
}

}

//对象流 ObjectOutputStream  ObjectInputStream

ObjectOutputStream objOutputStream = new ObjectOutputStream(    //写入
new FileOutputStream("123.txt"));

objOutputStream.writeObject(new Person(12, "jeck"));
objOutputStream.flush();
objOutputStream.close();
//读取
ObjectInputStream objectInputStream = new ObjectInputStream(
new FileInputStream("123.txt"));

Person person = (Person) objectInputStream.readObject();
System.out.println(person.getAge() + ":" + person.getName());
objectInputStream.close();

//编码

中文在GBK中2个字节，UTF—8中3个字节

String string="123中午";//编码
byte[]b=string.getBytes("GBK");
for (byte c : b) {
System.out.println(c);
}

 

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