98 lines
3.7 KiB
HTML
98 lines
3.7 KiB
HTML
<body>
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<h1>Java HDF5 Interface (JHI5)</h1>
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<h2><u>What it is</u></h2>
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The <b>Java HD5 Interface (JHI5)</b> is a Java package
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(<a href="../../hdf-java-html/javadocs/hdf/hdf5lib/package-summary.html">hdf.hdf5lib</a>)
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that ``wraps around'' the HDF5 library.
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<p>There are a large number of functions in the HDF5
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library (version 1.10). Some of the functions are not supported in JHI5. Most
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of the unsupported functions have C function pointers, which is not currently
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implemented in JHI5.</p>
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<table style="width:71%;text-align:center;background-color:#dbeaf5" border="1">
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<caption>Java HDF5 Interface (JHI5)</caption>
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<tr>
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<td style="text-align:center;">
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Note: The JHI5 does not support HDF4 or earlier.
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</td>
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</tr>
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</table>
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<p>The JHI5 may be used by any Java application that needs to access HDF5
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files. It is extremely important to emphasize that <i>this package is not
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a pure Java implementation of the HDF5 library.</i> The JHI5 calls the
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same HDF5 library that is used by C or FORTRAN programs. (Note that this
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product cannot be used in most network browsers because it accesses the
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local disk using native code.)
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<p>The Java HDF5 Interface consists of Java classes and a dynamically
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linked native library. The Java classes declare native methods, and the
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library contains C functions which implement the native methods. The C
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functions call the standard HDF5 library, which is linked as part of the
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same library on most platforms.
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<p>The central part of the JHI5 is the Java class <i>
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<a href="../../hdf-java-html/javadocs/hdf/hdf5lib/H5.html">hdf.hdf5lib.H5</a></i>.
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The <i>H5 </i>class calls the standard (<i>i.e.</i>, `native' code) HDF5
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library, with native methods for most of the HDF5 functions.
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<h3>
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<u>How to use it</u></h3>
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The JHI5 is used by Java classes to call the HDF5 library, in order to
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create HDF5 files, and read and write data in existing HDF5 files.
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<p>For example, the HDF5 library has the function <b>H5Fopen</b> to open
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an HDF5 file. The Java interface is the class <i>
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<a href="../../hdf-java-html/javadocs/hdf/hdf5lib/H5.html">hdf.hdf5lib.H5</a></i>,
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which has a method:
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<pre><b>static native int H5Fopen(String filename, int flags, int access );</b></pre>
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The native method is implemented in C using the
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<a href="http://java.sun.com/javase/6/docs/technotes/guides/jni/index.html">Java
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Native Method Interface </a>(JNI). This is written something like the following:
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<pre><b>JNIEXPORT jlong
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JNICALL Java_hdf_hdf5lib_H5_H5Fopen
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(
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JNIEnv *env,
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jclass class,
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jstring hdfFile,
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jint flags,
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jlong access)
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{
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/* ...convert Java String to (char *) */
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/* call the HDF library */
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retVal = H5Fopen((char *)file, (unsigned)flags, (hid_t)access);
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/* ... */
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}</b></pre>
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This C function calls the HDF5 library and returns the result appropriately.
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<p>There is one native method for each HDF entry point (several hundred
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in all), which are compiled with the HDF library into a dynamically loaded
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library (<i>libhdf5_java</i>). Note that this library must be built for each
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platform.
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<p>To call the HDF `<b><i>H5Fopen</i></b>' function, a Java program would
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import the package '<i><b>hdf.hdf5lib.*</b>'</i>, and invoke the method
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on the class '<b><i>H5</i></b>'. The Java program would look something
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like this:
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<pre><b>import hdf.hdf5lib.*;
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{
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/* ... */
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try {
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file = H5.Hopen("myFile.hdf", flags, access );
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} catch (HDF5Exception ex) {
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//...
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}
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/* ... */
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}</b></pre>
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The <i><b>H5</b> </i>class automatically loads the native method implementations
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and the HDF5 library.
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<h3>
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<a NAME="DOWNLOAD"></a>To Obtain</h3>
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The JHI5 is included with the <a href="https://portal.hdfgroup.org/display/support/Downloads">HDF5</a> library.
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</body>
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