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| <h2 title="Interface SharedClassTokenHelper" class="title">Interface SharedClassTokenHelper</h2> |
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| <pre>public interface <span class="typeNameLabel">SharedClassTokenHelper</span> |
| extends <a href="SharedClassHelper.html" title="interface in com.ibm.oti.shared">SharedClassHelper</a></pre> |
| <div class="block"><p>SharedClassHelper API that stores and finds classes using String tokens.</p> |
| <h2>Description</h2> |
| <p>A SharedClassTokenHelper is obtained by calling getTokenHelper(ClassLoader) on a SharedClassHelperFactory.</p> |
| <p>The SharedClassTokenHelper, which is the most simple type of helper, uses generated String tokens to find and store classes.</p> |
| <h2>Usage</h2> |
| <p>The ClassLoader should call findSharedClass after looking in its local cache and asking its parent (if one exists). |
| If findSharedClass does not return null, the ClassLoader calls defineClass on the byte[] that is returned.</p> |
| <p>The ClassLoader calls storeSharedClass immediately after a class is defined, unless the class that is being defined was loaded from the shared cache.</p> |
| <p>The ClassLoader is responsible for coordinating the creation of token Strings.</p> |
| <h2>Dynamic cache updates.</h2> |
| <p>Because the shared cache persists beyond the lifetime of a JVM, classes in the shared cache can become out of date (stale). |
| Using this helper, it is entirely the responsibility of the ClassLoader to ensure that cache entries are kept up-to-date. |
| Tokens have no meaning to the cache, so effectively turn the it into a dictionary of classes.</p> |
| <p>For example, a token may be the location where the class was found, combined with some type of versioning data.</p> |
| <p>If a ClassLoader stores multiple versions of the same class by using the same token, only the most recent will be returned by findSharedClass. </p> |
| <h2>Security</h2> |
| <p>A SharedClassHelper will only allow classes to be stored in the cache which were defined by the ClassLoader that owns the SharedClassHelper.</p> |
| <p>If a SecurityManager is installed, SharedClassPermissions must be used to permit read/write access to the shared class cache. |
| Permissions are granted by ClassLoader classname in the java.policy file and are fixed when the SharedClassHelper is created.</p> |
| <p>Note also that if the createClassLoader RuntimePermission is not granted, ClassLoaders cannot be created, |
| which in turn means that SharedClassHelpers cannot be created.</p> |
| <h2>Compatibility with other SharedClassHelpers</h2> |
| <p>Classes stored using the SharedClassTokenHelper cannot be retrieved using any other type of helper, and vice versa. </p></div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="SharedClassHelper.html" title="interface in com.ibm.oti.shared"><code>SharedClassHelper</code></a>, |
| <a href="SharedClassHelperFactory.html" title="interface in com.ibm.oti.shared"><code>SharedClassHelperFactory</code></a>, |
| <a href="SharedClassPermission.html" title="class in com.ibm.oti.shared"><code>SharedClassPermission</code></a></dd> |
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| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colSecond" scope="col">Method</th> |
| <th class="colLast" scope="col">Description</th> |
| </tr> |
| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code>byte[]</code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#findSharedClass(java.lang.String,java.lang.String)">findSharedClass</a></span>​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token, |
| <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> className)</code></th> |
| <td class="colLast"> |
| <div class="block">Finds a class in the shared cache by using a specific token and class name.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>boolean</code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#storeSharedClass(java.lang.String,java.lang.Class)">storeSharedClass</a></span>​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token, |
| <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Class.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">Class</a><?> clazz)</code></th> |
| <td class="colLast"> |
| <div class="block">Stores a class in the shared cache by using a specific token.</div> |
| </td> |
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| <h3>Methods declared in interface com.ibm.oti.shared.<a href="SharedClassHelper.html" title="interface in com.ibm.oti.shared">SharedClassHelper</a></h3> |
| <code><a href="SharedClassHelper.html#getSharingFilter()">getSharingFilter</a>, <a href="SharedClassHelper.html#setSharingFilter(com.ibm.oti.shared.SharedClassFilter)">setSharingFilter</a></code></li> |
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| <h3>Methods declared in interface com.ibm.oti.shared.<a href="SharedHelper.html" title="interface in com.ibm.oti.shared">SharedHelper</a></h3> |
| <code><a href="SharedHelper.html#getClassLoader()">getClassLoader</a></code></li> |
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| <h4>findSharedClass</h4> |
| <pre class="methodSignature">byte[] findSharedClass​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token, |
| <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> className)</pre> |
| <div class="block">Finds a class in the shared cache by using a specific token and class name.<p> |
| A class will be returned only for an exact String match of both the token and class name. |
| Otherwise, null is returned.<br> |
| To obtain an instance of the class, the byte[] returned must be passed to defineClass by the caller ClassLoader. |
| <p></div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>token</code> - String. |
| A token generated by the ClassLoader</dd> |
| <dd><code>className</code> - String. |
| The name of the class to be found</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>byte[]. |
| A byte array describing the class found, or null.</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="storeSharedClass(java.lang.String,java.lang.Class)"> |
| <!-- --> |
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| <h4>storeSharedClass</h4> |
| <pre class="methodSignature">boolean storeSharedClass​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token, |
| <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Class.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">Class</a><?> clazz)</pre> |
| <div class="block">Stores a class in the shared cache by using a specific token.<p> |
| The class that is being stored must have been defined by the caller ClassLoader.<br> |
| Returns <code>true</code> if the class is stored successfully or false otherwise.<br> |
| Will return <code>false</code> if the class that is being stored was not defined by the caller ClassLoader. |
| <p></div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>token</code> - String. |
| A token generated by the ClassLoader</dd> |
| <dd><code>clazz</code> - Class. |
| The class to store in the shared cache</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>boolean. |
| True if the class was stored successfully, false otherwise.</dd> |
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