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204 lines
8.3 KiB
HTML
204 lines
8.3 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Database Example</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="databases.html" title="Chapter 7. Databases" />
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<link rel="prev" href="DBAdmin.html" title="Administrative Methods" />
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<link rel="next" href="DBEntry.html" title="Chapter 8. Database Records" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Database Example</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="DBAdmin.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 7. Databases</th>
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<td width="20%" align="right"> <a accesskey="n" href="DBEntry.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="dbUsage"></a>Database Example</h2>
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</div>
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</div>
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</div>
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<p>In <a class="xref" href="dbenvUsageExample.html" title="Database Environment Management Example">Database Environment Management Example</a> we created a class that manages an
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<code class="classname">Environment</code>. We now extend that class to allow it
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to open and manage multiple databases. Again, remember that you can find
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this class in:
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</p>
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<pre class="programlisting"><span class="emphasis"><em>JE_HOME</em></span>/je/gettingStarted/MyDbEnv.java</pre>
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<p>
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where <code class="literal"><span class="emphasis"><em>JE_HOME</em></span></code> is the location where you
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placed your JE distribution.
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</p>
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<div class="example">
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<a id="mydbenvWDatabase"></a>
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<p class="title">
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<b>Example 7.1 Database Management with MyDbEnv</b>
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</p>
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<div class="example-contents">
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<p>First, we need to import a few additional classes, and setup some global variables to support databases.
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The databases that we are configuring and creating here are used by applications developed in examples later in this guide.</p>
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<a id="je_db10"></a>
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<pre class="programlisting">// File MyDbEnv.java
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package je.gettingStarted;
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import com.sleepycat.je.DatabaseException;
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<strong class="userinput"><code>import com.sleepycat.je.DatabaseConfig;
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import com.sleepycat.je.Database; </code></strong>
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import com.sleepycat.je.EnvironmentConfig;
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import com.sleepycat.je.Environment;
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import java.io.File;
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public class MyDbEnv {
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private Environment myEnv;
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<strong class="userinput"><code>private Database vendorDb;
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private Database inventoryDb;</code></strong>
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public MyDbEnv() {} </pre>
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<p>
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Next we need to update the <code class="methodname">MyDbEnv.setup()</code> method to instantiate a
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<code class="classname">DatabaseConfig</code> object. We also need to set some properties on that object. These property
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values are determined by the value of the <code class="literal">readOnly</code> parameter. We want our databases to be
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read-only if the environment is also read-only. We also want to allow our databases to be created if the databases
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are not read-only.
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</p>
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<a id="je_db11"></a>
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<pre class="programlisting"> public void setup(File envHome, boolean readOnly)
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throws DatabaseException {
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// Instantiate an environment <strong class="userinput"><code>and database</code></strong> configuration object
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EnvironmentConfig myEnvConfig = new EnvironmentConfig();
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<strong class="userinput"><code>DatabaseConfig myDbConfig = new DatabaseConfig();</code></strong>
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// Configure the environment <strong class="userinput"><code>and databases</code></strong> for the read-only
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// state as identified by the readOnly parameter on this
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// method call.
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myEnvConfig.setReadOnly(readOnly);
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<strong class="userinput"><code>myDbConfig.setReadOnly(readOnly);</code></strong>
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// If the environment is opened for write, then we want to be
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// able to create the environment <strong class="userinput"><code>and databases</code></strong> if
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// they do not exist.
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myEnvConfig.setAllowCreate(!readOnly);
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<strong class="userinput"><code>myDbConfig.setAllowCreate(!readOnly);</code></strong>
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// Instantiate the Environment. This opens it and also possibly
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// creates it.
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myEnv = new Environment(envHome, myEnvConfig);
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<strong class="userinput"><code>// Now create and open our databases.
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vendorDb = myEnv.openDatabase(null,
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"VendorDB",
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myDbConfig);
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inventoryDb = myEnv.openDatabase(null,
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"InventoryDB",
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myDbConfig);</code></strong>
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} </pre>
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<p>
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Next we need some additional getter methods used to return our database handles.
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</p>
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<a id="je_db12"></a>
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<pre class="programlisting"> // Getter methods
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public Environment getEnvironment() {
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return myEnv;
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}
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<strong class="userinput"><code>public Database getVendorDB() {
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return vendorDb;
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}
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public Database getInventoryDB() {
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return inventoryDb;
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}</code></strong> </pre>
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<p>
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Finally, we need to update the <code class="methodname">MyDbEnv.close()</code> method to close our databases.
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</p>
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<a id="je_db13"></a>
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<pre class="programlisting"> // Close the environment
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public void close() {
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if (myEnv != null) {
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try {
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<strong class="userinput"><code>vendorDb.close();
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inventoryDb.close();</code></strong>
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myEnv.close();
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} catch(DatabaseException dbe) {
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System.err.println("Error closing MyDbEnv: " +
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dbe.toString());
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System.exit(-1);
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}
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}
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}
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}</pre>
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<p>We can now use <code class="classname">MyDbEnv</code> to open and close
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both database environments and databases from the appropriate place in
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our application. For example:</p>
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<a id="je_db14"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.je.DatabaseException;
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<strong class="userinput"><code>import com.sleepycat.je.Database;</code></strong>
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import java.io.File;
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...
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MyDbEnv exampleDbEnv = new MyDbEnv();
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try {
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exampleDbEnv.setup(new File("/directory/currently/exists"), true);
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<strong class="userinput"><code>Database vendorDb = exampleDbEnv.getVendorDB();
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Database inventoryDB = exampleDbEnv.getInventoryDB();</code></strong>
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...
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} catch(DatabaseException dbe) {
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// Error code goes here
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} finally {
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exampleDbEnv.close();
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} </pre>
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</div>
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</div>
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<br class="example-break" />
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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||
<tr>
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||
<td width="40%" align="left"><a accesskey="p" href="DBAdmin.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="databases.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="DBEntry.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Administrative Methods </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Chapter 8. Database Records</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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