我正在尝试使用属性修改 Java 中的配置文件。
我使用 Properties.store、load 和 setProperty 成功地读取、写入和修改了这些行，但我注意到在执行此类操作后，文件被覆盖，因此我松开了配置文件中不是键值对的所有行。即，我失去了评论。
有没有办法使用 java.util 保留这样的行？
在每一行中放置一个前缀不是问题。我知道如何“手动”逐行阅读；我要求的是另一种选择
问问题
1869 次
2 回答
2
我不认为这是可能的。请注意，属性也不保证从 load() 到 store() 或从一个 store() 到另一个的顺序相同。如果可能，Properties 的 javadoc 会告诉您如何操作。
于 2013-08-23T12:47:08.240 回答
0
import java.io.*;
import java.util.*;
/**
* The CommentedProperties class is an extension of java.util.Properties
* to allow retention of comment lines and blank (whitespace only) lines
* in the properties file.
*
* Written for Java version 1.4
*/
public class CommentedProperties extends java.util.Properties {
/**
* Use a Vector to keep a copy of lines that are a comment or 'blank'
*/
public Vector lineData = new Vector(0, 1);
/**
* Use a Vector to keep a copy of lines containing a key, i.e. they are a property.
*/
public Vector keyData = new Vector(0, 1);
/**
* Load properties from the specified InputStream.
* Overload the load method in Properties so we can keep comment and blank lines.
* @param inStream The InputStream to read.
*/
public void load(InputStream inStream) throws IOException
{
// The spec says that the file must be encoded using ISO-8859-1.
BufferedReader reader =
new BufferedReader(new InputStreamReader(inStream, "ISO-8859-1"));
String line;
while ((line = reader.readLine()) != null) {
char c = 0;
int pos = 0;
// Leading whitespaces must be deleted first.
while ( pos < line.length()
&& Character.isWhitespace(c = line.charAt(pos))) {
pos++;
}
// If empty line or begins with a comment character, save this line
// in lineData and save a "" in keyData.
if ( (line.length() - pos) == 0
|| line.charAt(pos) == '#' || line.charAt(pos) == '!') {
lineData.add(line);
keyData.add("");
continue;
}
// The characters up to the next Whitespace, ':', or '='
// describe the key. But look for escape sequences.
// Try to short-circuit when there is no escape char.
int start = pos;
boolean needsEscape = line.indexOf('\\', pos) != -1;
StringBuffer key = needsEscape ? new StringBuffer() : null;
while ( pos < line.length()
&& ! Character.isWhitespace(c = line.charAt(pos++))
&& c != '=' && c != ':') {
if (needsEscape && c == '\\') {
if (pos == line.length()) {
// The line continues on the next line. If there
// is no next line, just treat it as a key with an
// empty value.
line = reader.readLine();
if (line == null)
line = "";
pos = 0;
while ( pos < line.length()
&& Character.isWhitespace(c = line.charAt(pos)))
pos++;
} else {
c = line.charAt(pos++);
switch (c) {
case 'n':
key.append('\n');
break;
case 't':
key.append('\t');
break;
case 'r':
key.append('\r');
break;
case 'u':
if (pos + 4 <= line.length()) {
char uni = (char) Integer.parseInt
(line.substring(pos, pos + 4), 16);
key.append(uni);
pos += 4;
} // else throw exception?
break;
default:
key.append(c);
break;
}
}
} else if (needsEscape)
key.append(c);
}
boolean isDelim = (c == ':' || c == '=');
String keyString;
if (needsEscape)
keyString = key.toString();
else if (isDelim || Character.isWhitespace(c))
keyString = line.substring(start, pos - 1);
else
keyString = line.substring(start, pos);
while ( pos < line.length()
&& Character.isWhitespace(c = line.charAt(pos)))
pos++;
if (! isDelim && (c == ':' || c == '=')) {
pos++;
while ( pos < line.length()
&& Character.isWhitespace(c = line.charAt(pos)))
pos++;
}
// Short-circuit if no escape chars found.
if (!needsEscape) {
put(keyString, line.substring(pos));
// Save a "" in lineData and save this
// keyString in keyData.
lineData.add("");
keyData.add(keyString);
continue;
}
// Escape char found so iterate through the rest of the line.
StringBuffer element = new StringBuffer(line.length() - pos);
while (pos < line.length()) {
c = line.charAt(pos++);
if (c == '\\') {
if (pos == line.length()) {
// The line continues on the next line.
line = reader.readLine();
// We might have seen a backslash at the end of
// the file. The JDK ignores the backslash in
// this case, so we follow for compatibility.
if (line == null)
break;
pos = 0;
while ( pos < line.length()
&& Character.isWhitespace(c = line.charAt(pos)))
pos++;
element.ensureCapacity(line.length() - pos +
element.length());
} else {
c = line.charAt(pos++);
switch (c) {
case 'n':
element.append('\n');
break;
case 't':
element.append('\t');
break;
case 'r':
element.append('\r');
break;
case 'u':
if (pos + 4 <= line.length()) {
char uni = (char) Integer.parseInt
(line.substring(pos, pos + 4), 16);
element.append(uni);
pos += 4;
} // else throw exception?
break;
default:
element.append(c);
break;
}
}
} else
element.append(c);
}
put(keyString, element.toString());
// Save a "" in lineData and save this
// keyString in keyData.
lineData.add("");
keyData.add(keyString);
}
}
/**
* Write the properties to the specified OutputStream.
*
* Overloads the store method in Properties so we can put back comment
* and blank lines.
*
* @param out The OutputStream to write to.
* @param header Ignored, here for compatability w/ Properties.
*
* @exception IOException
*/
public void store(OutputStream out, String header) throws IOException
{
// The spec says that the file must be encoded using ISO-8859-1.
PrintWriter writer
= new PrintWriter(new OutputStreamWriter(out, "ISO-8859-1"));
// We ignore the header, because if we prepend a commented header
// then read it back in it is now a comment, which will be saved
// and then when we write again we would prepend Another header...
String line;
String key;
StringBuffer s = new StringBuffer ();
for (int i=0; i<lineData.size(); i++) {
line = (String) lineData.get(i);
key = (String) keyData.get(i);
if (key.length() > 0) { // This is a 'property' line, so rebuild it
formatForOutput (key, s, true);
s.append ('=');
formatForOutput ((String) get(key), s, false);
writer.println (s);
} else { // was a blank or comment line, so just restore it
writer.println (line);
}
}
writer.flush ();
}
/**
* Need this method from Properties because original code has StringBuilder,
* which is an element of Java 1.5, used StringBuffer instead (because
* this code was written for Java 1.4)
*
* @param str - the string to format
* @param buffer - buffer to hold the string
* @param key - true if str the key is formatted, false if the value is formatted
*/
private void formatForOutput(String str, StringBuffer buffer, boolean key)
{
if (key) {
buffer.setLength(0);
buffer.ensureCapacity(str.length());
} else
buffer.ensureCapacity(buffer.length() + str.length());
boolean head = true;
int size = str.length();
for (int i = 0; i < size; i++) {
char c = str.charAt(i);
switch (c) {
case '\n':
buffer.append("\\n");
break;
case '\r':
buffer.append("\\r");
break;
case '\t':
buffer.append("\\t");
break;
case ' ':
buffer.append(head ? "\\ " : " ");
break;
case '\\':
case '!':
case '#':
case '=':
case ':':
buffer.append('\\').append(c);
break;
default:
if (c < ' ' || c > '~') {
String hex = Integer.toHexString(c);
buffer.append("\\u0000".substring(0, 6 - hex.length()));
buffer.append(hex);
} else
buffer.append(c);
}
if (c != ' ')
head = key;
}
}
/**
* Add a Property to the end of the CommentedProperties.
*
* @param keyString The Property key.
* @param value The value of this Property.
*/
public void add(String keyString, String value)
{
put(keyString, value);
lineData.add("");
keyData.add(keyString);
}
/**
* Add a comment or blank line or comment to the end of the CommentedProperties.
*
* @param line The string to add to the end, make sure this is a comment
* or a 'whitespace' line.
*/
public void addLine(String line)
{
lineData.add(line);
keyData.add("");
}
}
于 2013-08-23T13:33:57.043 回答