Java中文件读取
1、预处理文件。这里有三种格式的源文件。包括
1. 占用空间117M，大小70.1M的21471个小文件组成的文件夹
2. 上述小文件通过zip格式压缩后形成的zip文件，大小33.9M
3. 上述小文件写在一个文件中后的一个大文件70.3M（每个文件占用两行，第一行为文件名，第二行为文件内容）
2、分别通过默认的带有Buffer的字节输入流与字符输入流来读取三种格式的文件。（缓冲区使用默认的8k，参考资料中说明了8k是一个综合效果较好的缓冲区大小）。代码在下一个“代码”部分。
3、下面是结果示例，可以看到
1. 字节流明显比字符流有更快的速度，只是有时候可能需要使用字符流来方便进行人机交互。
2. 小文件由于打开IO频繁，其效率是最慢的
3. 带有Buffer的大文件是其中速度最快的，但是由于将多个文件组合在一个文件中，这个就需要自己设置分割方式，以及区分的办法了
4. zip文件居中
5. 在本次实验中对于字节流的读写，速度大概是1:10:100的比例
对于字符流的速度大约是1:4:20的样子
1、三种格式文件读取代码：
public static File[] get()//读取一个大文件
{
return new File[]{new File("C:/Users/Administrator/Desktop/文件存取/zh_en.txt")};
}
public static File [] get()//读取多个小文件
{
return new File("C:/Users/Administrator/Desktop/文件存取/zh_en").listFiles();
}
public static ZipInputStream get() throws IOException//读取zip文件
{
return new ZipInputStream(new BufferedInputStream(new FileInputStream(new File("C:/Users/Administrator/Desktop/文件存取/zh_en.zip"))));
}
2、zip文件测试
public static void main(String[] args) throws IOException
{
System.out.println("StrTime\t" + Time());
System.out.println("StreamTime\t" + Time2());
}
private static long Time() throws IOException
{
ZipInputStream zis = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
ZipEntry entry;
BufferedReader br = new BufferedReader(new InputStreamReader(zis));
while ((entry = zis.getNextEntry()) != null)
{
if(!entry.isDirectory())
{
String line = "";
while((line = br.readLine()) != null)
{
all += line.length();
}
}
zis.closeEntry();
}
br.close();
zis.close();
System.out.println(all);
return System.currentTimeMillis() - start;
}
private static long Time2() throws IOException
{
ZipInputStream zis = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
ZipEntry entry;
while ((entry = zis.getNextEntry()) != null)
{
if(!entry.isDirectory())
{
byte [] temp = new byte[1024];
int length = 0;
while((length = zis.read(temp)) > 0)
{
all += length;
}
}
zis.closeEntry();
}
zis.close();
System.out.println(all);
return System.currentTimeMillis() - start;
}
3、多个小文件测试
public static void main(String[] args) throws IOException
{
System.out.println("StreamIOFilesTime\t" + StreamIOFilesTime());
System.out.println("StrIOFilesTime\t" + StrIOFilesTime());
System.out.println("RandomIOFilesTime\t" + RandomIOFilesTime());
}
private static long RandomIOFilesTime() throws IOException
{
File [] files = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
for (File file : files)
{
byte [] temp = new byte[1024];
int length = 0;
RandomAccessFile rfile = new RandomAccessFile(file, "r");
while((length = rfile.read(temp)) > 0)
{
all += length;
}
rfile.close();
}
System.out.println(all);
return System.currentTimeMillis() - start;
}
private static long StreamIOFilesTime() throws IOException
{
File [] files = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
for (File file : files)
{
int length = 0;
BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
byte [] temp = new byte[1024];
while((length = bis.read(temp)) > 0)
{
all += length;
}
bis.close();
}
System.out.println(all);
return System.currentTimeMillis() - start;
}
private static long StrIOFilesTime() throws IOException
{
File [] files = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
for (File file : files)
{
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
String temp = "";
while((temp = br.readLine()) != null)
{
all += temp.length();
}
br.close();
}
System.out.println(all);
return System.currentTimeMillis() - start;
}
4、大文件测试
public static void main(String[] args) throws IOException
{
System.out.println("StreamIOFilesTime\t" + StreamIOFilesTime());
System.out.println("StrIOFilesTime\t" + StrIOFilesTime());
System.out.println("RandomIOFilesTime\t" + RandomIOFilesTime());
}
private static long RandomIOFilesTime() throws IOException
{
File [] files = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
for (File file : files)
{
byte [] temp = new byte[1024];
int length = 0;
RandomAccessFile rfile = new RandomAccessFile(file, "r");
while((length = rfile.read(temp)) > 0)
{
all += length;
}
rfile.close();
}
System.out.println(all);
return System.currentTimeMillis() - start;
}
private static long StreamIOFilesTime() throws IOException
{
File [] files = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
for (File file : files)
{
int length = 0;
BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
byte [] temp = new byte[1024];
while((length = bis.read(temp)) > 0)
{
all += length;
}
bis.close();
}
System.out.println(all);
return System.currentTimeMillis() - start;
}
private static long StrIOFilesTime() throws IOException
{
File [] files = GiveFiles.get();
long start = System.currentTimeMillis();
int all = 0;
for (File file : files)
{
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
String temp = "";
while((temp = br.readLine()) != null)
{
all += temp.length();
}
br.close();
}
System.out.println(all);
return System.currentTimeMillis() - start;
}