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<div class="subTitle">com.ibm.oti.shared</div>
<h2 title="Interface SharedDataHelper" class="title">Interface SharedDataHelper</h2>
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<pre>public interface <span class="typeNameLabel">SharedDataHelper</span>
extends <a href="../../../../com/ibm/oti/shared/SharedHelper.html" title="interface in com.ibm.oti.shared">SharedHelper</a></pre>
<div class="block"><p>SharedDataHelper API that stores and finds byte data using String tokens.</p>
<h3>Description</h3>
<p>A SharedDataHelper is obtained by calling getSharedDataHelper(ClassLoader) on a SharedDataHelperFactory.</p>
<p>The SharedDataHelper allows byte data to be written into the shared class cache and shared with other VMs.</p>
<p>Byte data to be stored in the cache should exist in a java.nio.ByteBuffer which is copied to the cache when
storeSharedData() is called. The function returns a read-only java.nio.ByteBuffer which is the shared copy of the data.
Any subsequent changes to the ByteBuffer are therefore not reflected in the cache unless it is re-stored.</p>
<p>Byte data is found in the cache by calling findSharedData() which returns a read-only java.nio.ByteBuffer which
maps to the byte data that exists in the cache.</p>
<h3>Tokens</h3>
<p>A String token is chosen/generated by the application which is using the Helper and should ideally include a unique
identifier and some kind of versioning information. Eg. com.foo.myApp31_myDoozerData_003. The important factor is that
other VMs running the same application should be able to apply the same algorithm and find the data. </p>
<h3>Dynamic Cache Updates</h3>
<p>Since the shared cache is persistent beyond the lifetime of a JVM, data in the shared cache may become out-of-date (<q>stale</q>).
Using this helper, it is entirely the responsibility of the application to ensure that cache entries are kept up-to-date.
Tokens have no meaning to the cache, so effectively turn it into a dictionary of classes.</p>
<p>Eg. A token may be the location where the class was found, combined with some type of versioning data.</p>
<p>If an application stores multiple versions of the same data using the same token, only the most recent will be returned by findSharedData.</p></div>
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<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="../../../../com/ibm/oti/shared/SharedHelper.html" title="interface in com.ibm.oti.shared"><code>SharedHelper</code></a>,
<a href="../../../../com/ibm/oti/shared/SharedDataHelperFactory.html" title="interface in com.ibm.oti.shared"><code>SharedDataHelperFactory</code></a>,
<a href="../../../../com/ibm/oti/shared/SharedClassPermission.html" title="class in com.ibm.oti.shared"><code>SharedClassPermission</code></a></dd>
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<h3>Method Summary</h3>
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<td class="colFirst"><code><a href="https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html?is-external=true" target="_blank" title="class or interface in java.nio">ByteBuffer</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../com/ibm/oti/shared/SharedDataHelper.html#findSharedData-java.lang.String-">findSharedData</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" target="_blank" title="class or interface in java.lang">String</a>&nbsp;token)</code>
<div class="block">Find data in the shared cache using a specific token.</div>
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<td class="colFirst"><code><a href="https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html?is-external=true" target="_blank" title="class or interface in java.nio">ByteBuffer</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../com/ibm/oti/shared/SharedDataHelper.html#storeSharedData-java.lang.String-java.nio.ByteBuffer-">storeSharedData</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" target="_blank" title="class or interface in java.lang">String</a>&nbsp;token,
<a href="https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html?is-external=true" target="_blank" title="class or interface in java.nio">ByteBuffer</a>&nbsp;data)</code>
<div class="block">Store data in the shared cache using a specific token.</div>
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<h3>Methods inherited from interface&nbsp;com.ibm.oti.shared.<a href="../../../../com/ibm/oti/shared/SharedHelper.html" title="interface in com.ibm.oti.shared">SharedHelper</a></h3>
<code><a href="../../../../com/ibm/oti/shared/SharedHelper.html#getClassLoader--">getClassLoader</a></code></li>
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<h4>findSharedData</h4>
<pre><a href="https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html?is-external=true" target="_blank" title="class or interface in java.nio">ByteBuffer</a>&nbsp;findSharedData(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" target="_blank" title="class or interface in java.lang">String</a>&nbsp;token)</pre>
<div class="block">Find data in the shared cache using a specific token.<p>
Data will be returned only for an exact String match of the token. Otherwise, null is returned.<br>
The ByteBuffer returned is read-only and cannot be modified.<br>
If a SecurityManager is installed, findSharedData can only be called by code whose caller-classloader
has been granted <q>read</q> permissions to the shared class cache.
<p></div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>token</code> - String.
A String token to be used as a key</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>ByteBuffer.
A read-only ByteBuffer containing the cached data, or null.</dd>
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<h4>storeSharedData</h4>
<pre><a href="https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html?is-external=true" target="_blank" title="class or interface in java.nio">ByteBuffer</a>&nbsp;storeSharedData(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" target="_blank" title="class or interface in java.lang">String</a>&nbsp;token,
<a href="https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html?is-external=true" target="_blank" title="class or interface in java.nio">ByteBuffer</a>&nbsp;data)</pre>
<div class="block">Store data in the shared cache using a specific token.<p>
If the data is stored successfully, the shared read-only copy of the data is returned. Otherwise, null is returned.<br>
If data already exists for the token specified, the old data is marked <q>stale</q> in the cache and is replaced by the new data.<br>
If the exact same data already exists in the cache under the same token, the data is not duplicated and the cached version is returned.<br>
If null is passed as the data argument, the data currently stored against that token is marked "stale" and null is returned.<br>
If a SecurityManager is installed, storeSharedData can only be called by code whose caller-classloader
has been granted <q>write</q> permissions to the shared class cache.
<p></div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>token</code> - String.
A String token to be used as a key</dd>
<dd><code>data</code> - ByteBuffer.
A ByteBuffer of data to copy to the cache</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>ByteBuffer.
A read-only ByteBuffer containing the cached data, or null.</dd>
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