该文章来自我的个人博客:
Java的I/O系统
FilenameFilter
文件过滤器,获取指定的文件
import java.io.File;
import java.io.FilenameFilter;
import java.util.regex.Pattern;
public class Filenamer {
public static void main(String...args){
File path=new File(".");
String[] files;
if(args.length==){
files=path.list();
}else{
files=path.list(new DirFilter(args[]));
}
if(files==null){
return;
}
for(String file:files){
System.out.println("file:"+file);
}
}
}
class DirFilter implements FilenameFilter {
private Pattern pattern;
public DirFilter(String regex){
pattern=Pattern.compile(regex);
}
@Override
public boolean accept(File pathname,String name) {
return pattern.matcher(name).matches();
}
}
DirFilter重写了FilenameFilter的accept方法根据传入的正则判断出符合条件的文件名,符合返回true,不符合返回false
accept方法供list方法调用,list方法源码如下:
public String[] list(FilenameFilter filter) {
String names[] = list();
if ((names == null) || (filter == null)) {
return names;
}
List<String> v = new ArrayList<>();
for (int i = ; i < names.length ; i++) {
if (filter.accept(this, names[i])) {
v.add(names[i]);
}
}
return v.toArray(new String[v.size()]);
}
输入
读取文件到缓存
BufferedReader in=new BufferedReader(new FileReader(fileName));
while((str=in.readLine())!=null){
strs.append(str);
}
读取字符串到内存
StringReader in=new StringReader(str);
//in。read返回字符的Ascall码,内容读取完则返回-1
while((c=in.read())!=-){
System.out.println((char)c);
}
读取字节到内存
//new ByteArrayInputStream()将字节数组转换成字节流
DataInputStream in=new DataInputStream(new ByteArrayInputStream(str.getBytes());
//in.readByte()返回下一个字节,当已经到达末尾,会抛出EOFException异常
while(in.available()!=){
System.out.println((char)in.readByte())
}
输出
写内容到文件
PrintWriter out=new PrintWriter(new BufferedWriter(new FileWriter(fileName)));
out.println(str);
存储和恢复数据
try {
DataOutputStream out=new DataOutputStream(new BufferedOutputStream(new FileOutputStream("test.txt")));
out.writeChar('c');
out.writeBoolean(true);
out.writeDouble();
out.writeUTF("str");
out.close();
DataInputStream in=new DataInputStream(new BufferedInputStream(new FileInputStream("test.txt")));
//注意读取有顺序区分
System.out.println(in.readChar()+" "+in.readBoolean()+" "+in.readDouble()+" "+in.readUTF());
in.close();
} catch (IOException e) {
e.printStackTrace();
}
c true 12.3222222 str
随机存储访问数据
String fileName="test.txt";
try {
RandomAccessFile out=new RandomAccessFile(fileName,"rw");
out.writeDouble();
out.writeDouble();
out.writeDouble();
out.writeDouble();
out.writeDouble();
out.close();
RandomAccessFile in=new RandomAccessFile(fileName,"rw");
System.out.println(in.readDouble()+" "+in.readDouble()+" "+in.readDouble()+" "+in.readDouble()+" "+in.readDouble()+" ");
//in.close();
out=new RandomAccessFile(fileName,"rw");
//一个double数值为字节
out.seek();
out.writeDouble();
out.close();
//in=new RandomAccessFile(fileName,"r");
//回到开始位置,重新读取数据
in.seek();
System.out.println(in.readDouble()+" "+in.readDouble()+" "+in.readDouble()+" "+in.readDouble()+" "+in.readDouble()+" ");
in.close();
}catch (IOException e){
e.printStackTrace();
}
0.0 0.1 0.2 0.3 0.4
0.0 1.0 0.2 0.3 0.4