看别人的程序,在更新 xml 文件的时候,是先 创建一个临时文件,把新数据写入这个临时文件,说是为了最大化安全。最后再把原文件删除,更新临时文件名为原文件名,所谓“安全”, 是担心写磁盘xml文件的时候出现某故障,导致 xml 文件格式出问题吗 ?
部分代码如下:
/**
* Saves the properties to disk as an XML document. A temporary file is
* used during the writing process for maximum safety.
*/
private synchronized void saveProperties() {
OutputStream out = null;
boolean error = false;
// Write data out to a temporary file first.
File tempFile = null;
try {
tempFile = new File(file.getParentFile(), file.getName() + ".tmp");
// Use JDOM's XMLOutputter to do the writing and formatting. The
// file should always come out pretty-printed.
XMLOutputter outputter = new XMLOutputter(" ", true);
out = new BufferedOutputStream(new FileOutputStream(tempFile));
outputter.output(doc, out);
}
catch (Exception e) {
e.printStackTrace();
// There were errors so abort replacing the old property file.
error = true;
}
finally {
try { out.close(); }
catch (Exception e) {
e.printStackTrace();
error = true;
}
}
// No errors occured, so we should be safe in replacing the old
if (!error) {
// Delete the old file so we can replace it.
file.delete();
// Rename the temp file. The delete and rename won't be an
// automic operation, but we should be pretty safe in general.
// At the very least, the temp file should remain in some form.
tempFile.renameTo(file);
}
}
部分代码如下:
/**
* Saves the properties to disk as an XML document. A temporary file is
* used during the writing process for maximum safety.
*/
private synchronized void saveProperties() {
OutputStream out = null;
boolean error = false;
// Write data out to a temporary file first.
File tempFile = null;
try {
tempFile = new File(file.getParentFile(), file.getName() + ".tmp");
// Use JDOM's XMLOutputter to do the writing and formatting. The
// file should always come out pretty-printed.
XMLOutputter outputter = new XMLOutputter(" ", true);
out = new BufferedOutputStream(new FileOutputStream(tempFile));
outputter.output(doc, out);
}
catch (Exception e) {
e.printStackTrace();
// There were errors so abort replacing the old property file.
error = true;
}
finally {
try { out.close(); }
catch (Exception e) {
e.printStackTrace();
error = true;
}
}
// No errors occured, so we should be safe in replacing the old
if (!error) {
// Delete the old file so we can replace it.
file.delete();
// Rename the temp file. The delete and rename won't be an
// automic operation, but we should be pretty safe in general.
// At the very least, the temp file should remain in some form.
tempFile.renameTo(file);
}
}
解决方案 »
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