?? linefilter2.html
字號:
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<TITLE>Implementing a FilterReader to Filter Lines Based on a Regular Expression
(Java Developers Almanac Example)
</TITLE>
<META CONTENT="Patrick Chan" NAME="AUTHOR">
<META CONTENT="Code Examples from The Java Developers Almanac 1.4" NAME="DESCRIPTION">
<META CONTENT="Addison-Wesley/Patrick Chan" NAME="OWNER">
<META CONTENT="3/20/02" NAME="revision">
<STYLE TYPE="text/css">
<!-- BODY CODE {font-family: Courier, Monospace; font-size: 11pt} TABLE, BODY {font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 10pt} PRE {font-family: Courier, Monospace; font-size: 10pt} H3 {font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 11pt} A.eglink {text-decoration: none} A:hover.eglink {text-decoration: underline} -->
</STYLE>
</HEAD>
<BODY>
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD rowspan="3"><A HREF="/?l=ex"><IMG BORDER="0" ALIGN="BOTTOM" HSPACE="10" SRC="/egs/almanac14a.jpg"></A></TD><TD VALIGN="top"><font face="Times" size="6"><b>The Java Developers Almanac 1.4</b></font>
<br>
Order this book from <a href="/cgi-bin/scripts/redirect.pl?l=ex&url=http://www.amazon.com/exec/obidos/ASIN/0201752808/xeo">Amazon</a>.
</TD>
</TR>
<TR>
<TD align="right" valign="bottom">
<FORM method="get" action="/cgi-bin/search/find.pl">
<INPUT size="25" name="words" type="text"><INPUT value="Search" type="submit">
</FORM>
</TD>
</TR>
</TABLE>
<HR color="#6666cc">
<DIV ALIGN="LEFT">
<A HREF="/">Home</A>
>
<A HREF="../index.html">List of Packages</A>
>
<B><A HREF="../java.util.regex/pkg.html">java.util.regex</A></B><font color="#666666" SIZE="-2">
[26 examples]
</font>
>
<B><A HREF="../java.util.regex/pkg.html#Lines">Lines</A></B><font color="#666666" SIZE="-2">
[6 examples]
</font>
</DIV><P>
<h3>
e442.
Implementing a FilterReader to Filter Lines Based on a Regular Expression</h3>
A common use of regular expressions is to find all lines that match a
pattern, similar to the <code>grep</code> Unix command. This example implements a
<code>FilterReader</code> that will filter an input stream based on a pattern.
<pre>
try {
// Create the FilterReader
String filename = <font color="#0066ff"><i>"infile.txt"</i></font>;
String pattern = <font color="#0066ff"><i>"pattern"</i></font>;
BufferedReader rd = new BufferedReader(new FileReader(filename));
rd = new BufferedReader(new RegexReader(rd, pattern));
// Retrieve all lines that match pattern
String line = null;
while ((line = rd.readLine()) != null) {
// line matches the pattern
}
} catch (IOException e) {
}
// This class takes a reader and a pattern and removes lines
// that don't match the pattern.
// Line terminators are converted to a \n.
public class RegexReader extends FilterReader {
// This variable holds the current line.
// If null and emitNewline is false, a newline must be fetched.
String curLine;
// This is the index of the first unread character in curLine.
// If at any time curLineIx == curLine.length, curLine is set to null.
int curLineIx;
// If true, the newline at the end of curLine has not been returned.
// It would have been more convenient to append the newline
// onto freshly fetched lines. However, that would incur another
// allocation and copy.
boolean emitNewline;
// Matcher used to test every line
Matcher matcher;
public RegexReader(BufferedReader in, String patternStr) {
super(in);
Pattern pattern = Pattern.compile(patternStr);
matcher = pattern.matcher("");
}
// This overridden method fills cbuf with characters read from in.
public int read(char cbuf[], int off, int len) throws IOException {
// Fetch new line if necessary
if (curLine == null && !emitNewline) {
getNextLine();
}
// Return characters from current line
if (curLine != null) {
int num = Math.min(len, Math.min(cbuf.length-off,
curLine.length()-curLineIx));
// Copy characters from curLine to cbuf
for (int i=0; i<num; i++) {
cbuf[off++] = curLine.charAt(curLineIx++);
}
// No more characters in curLine
if (curLineIx == curLine.length()) {
curLine = null;
// Is there room for the newline?
if (num < len && off < cbuf.length) {
cbuf[off++] = '\n';
emitNewline = false;
num++;
}
}
// Return number of character read
return num;
} else if (emitNewline && len > 0) {
// Emit just the newline
cbuf[off] = '\n';
emitNewline = false;
return 1;
} else if (len > 0) {
// No more characters left in input reader
return -1;
} else {
// Client did not ask for any characters
return 0;
}
}
// Get next matching line
private void getNextLine() throws IOException {
curLine = ((BufferedReader)in).readLine();
while (curLine != null) {
matcher.reset(curLine);
if (matcher.find()) {
emitNewline = true;
curLineIx = 0;
return;
}
curLine = ((BufferedReader)in).readLine();
}
return;
}
public boolean ready() throws IOException {
return curLine != null || emitNewline || in.ready();
}
public boolean markSupported() {
return false;
}
}
</pre>
<P><table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td bgcolor="#6666cc" align="center"><font color="#ffffff">
Related Examples
</font></td>
</tr>
</table>
e441. <a class="eglink" href="LineFilter.html?l=rel">
Using a Regular Expression to Filter Lines from a Reader
</a>
<br>
e443. <a class="eglink" href="Line.html?l=rel">
Matching Line Boundaries in a Regular Expression
</a>
<br>
e444. <a class="eglink" href="Lines.html?l=rel">
Matching Across Line Boundaries in a Regular Expression
</a>
<br>
e445. <a class="eglink" href="ReadLine.html?l=rel">
Reading Lines from a String Using a Regular Expression
</a>
<br>
e446. <a class="eglink" href="RemLine.html?l=rel">
Removing Line Termination Characters from a String
</a>
<br>
<table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td align="left">
<br>
See also:
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Flags">
Flags
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Groups">
Groups
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Paragraphs">
Paragraphs
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Searching%20and%20Replacing">
Searching and Replacing
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Tokenizing">
Tokenizing
</a>
</td>
</tr>
</table>
<br>
<br>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif" SIZE="0">
© 2002 Addison-Wesley.
</FONT>
</BODY>
</HTML>
?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -