csdn上碰到一个提问者希望只在\n时,才换行来读取文本文件的每一行。
但java的BufferedReader#readLine() 不区分\r 还是\n 都会换到下一行。
并且提问者的文件还特别大,不能一次全读到内存里来。
为了这个写了个自己的类。 (还没好好测过。。。有bug欢迎留言)
package sh.pl;
import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;
public class LineReader {
private static final int BUFFER_SIZE = 4096;
private Reader in;
private int bufferSize;
private List<String> bufferedLines;
private String lineSeparator;
private String preString;
public LineReader(Reader in) {
if (in == null) {
throw new IllegalArgumentException("in is null");
}
this.in = in;
bufferedLines = new ArrayList<String>();
lineSeparator = System.getProperty("line.separator");
bufferSize = BUFFER_SIZE;
}
public void close() throws IOException {
in.close();
}
public void setBufferSize(int bufferSize) {
if (bufferSize <= 0) {
throw new IllegalArgumentException("bufferSize <= 0");
}
this.bufferSize = bufferSize;
}
public void setLineSeparator(String lineSeparator) {
if (lineSeparator == null) {
throw new IllegalArgumentException("lineSeparator is null");
}
this.lineSeparator = lineSeparator;
}
public String readLine() throws IOException {
if (bufferedLines.size() > 1) {
return bufferedLines.remove(0);
} else if (bufferedLines.size() == 1) {
preString = bufferedLines.remove(0);
return readLine();
} else {
char[] src = new char[bufferSize];
int len;
if ((len = in.read(src)) != -1) {
String bufferString = new String(src, 0, len);
if (preString != null) {
bufferString = preString + bufferString;
preString = null;
}
boolean returnDelims = false;
StringTokenizer token = new StringTokenizer(bufferString,
lineSeparator, returnDelims);
while (token.hasMoreTokens()) {
bufferedLines.add(token.nextToken());
}
if (bufferString.endsWith(lineSeparator)) {
bufferedLines.add("");
}
return readLine();
} else {
if (preString != null) {
String ret = preString;
preString = null;
return ret;
} else {
return null;
}
}
}
}
}
使用
LineReader lr = null;
try {
lr = new LineReader(new InputStreamReader(new FileInputStream(
fileName), yourFileEncode));
//指定换行符
lr.setLineSeparator("\n");
String line;
while ((line = lr.readLine()) != null) {
System.out.println("'" + line + "'");
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (lr != null) {
try {
lr.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
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