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https://issues.apache.org/jira/browse/HADOOP-14076?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15863813#comment-15863813
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Ted Yu commented on HADOOP-14076:
---------------------------------
That's what I did using JNI:
{code}
void writeConf(jobject conf, const char *filepath)
{
jclass class_fdesc = (*env)->FindClass(env, "java/io/FileDescriptor");
// construct a new FileDescriptor
jmethodID const_fdesc = (*env)->GetMethodID(env, class_fdesc, "<init>",
"()V");
jobject file = (*env)->NewObject(env, class_fdesc, const_fdesc);
jfieldID field_fd = (*env)->GetFieldID(env, class_fdesc, "fd", "I");
int fd = open(filepath, O_RDWR | O_NONBLOCK | O_CREAT, S_IRWXU);
if (fd < 0) {
printf("Couldn't open file %s\n", filepath);
exit(-1);
}
(*env)->SetIntField(env, file, field_fd, fd);
jclass cls_outstream = (*env)->FindClass(env, "java/io/FileOutputStream");
jmethodID ctor_stream = (*env)->GetMethodID(env, cls_outstream, "<init>",
"(Ljava/io/FileDescriptor;)V");
if (ctor_stream == NULL) {
printf("Couldn't get ctor for FileOutputStream\n");
exit(-1);
}
jobject file_outstream = (*env)->NewObject(env, cls_outstream, ctor_stream,
file);
if (file_outstream == NULL) {
printf("Couldn't create FileOutputStream\n");
exit(-1);
}
jclass class_conf = (*env)->FindClass(env, HADOOP_CONF);
jmethodID writeXmlMid = (*env)->GetMethodID(env, class_conf, "writeXml",
"(Ljava/io/OutputStream;)V");
(*env)->CallObjectMethod(env, conf, writeXmlMid, file_outstream);
}
{code}
The code is tedious (manipulating fd field).
> Allow Configuration to be persisted given path to file
> ------------------------------------------------------
>
> Key: HADOOP-14076
> URL: https://issues.apache.org/jira/browse/HADOOP-14076
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Ted Yu
>
> Currently Configuration has the following methods for persistence:
> {code}
> public void writeXml(OutputStream out) throws IOException {
> public void writeXml(Writer out) throws IOException {
> {code}
> Adding API for persisting to file given path would be useful:
> {code}
> public void writeXml(String path) throws IOException {
> {code}
> Background: I recently worked on exporting Configuration to a file using JNI.
> Without the proposed API, I resorted to some trick such as the following:
> http://www.kfu.com/~nsayer/Java/jni-filedesc.html
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