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|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Using the BIND APIs</title>
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
<link rel="start" href="index.html" title="Getting Started with Berkeley DB" />
<link rel="up" href="DBEntry.html" title="Chapter 8. Database Records" />
<link rel="prev" href="usingDbt.html" title="Reading and Writing Database Records" />
<link rel="next" href="dbtJavaUsage.html" title="Database Usage Example" />
</head>
<body>
<div xmlns="" class="navheader">
<div class="libver">
<p>Library Version 12.1.6.1</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Using the BIND APIs</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="usingDbt.html">Prev</a> </td>
<th width="60%" align="center">Chapter 8. Database Records</th>
<td width="20%" align="right"> <a accesskey="n" href="dbtJavaUsage.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="bindAPI"></a>Using the BIND APIs</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="bindAPI.html#bindPrimitive">Numerical and String Objects</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="bindAPI.html#object2dbt">Serializable Complex Objects</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="bindAPI.html#customTuple">Custom Tuple Bindings</a>
</span>
</dt>
</dl>
</div>
<p>Except for Java String and boolean types, efficiently moving data in
and out of Java byte arrays for storage in a database can be a nontrivial
operation. To help you with this problem, DB provides the Bind APIs.
While these APIs are described in detail in the
<span>
<em class="citetitle">Berkeley DB Collections Tutorial</em>,
</span>
this section provides a brief introduction to using the Bind APIs with:</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>Single field numerical and string objects</p>
<p>Use this if you want to store a single numerical or string object,
such as <code class="classname">Long</code>, <code class="classname">Double</code>, or
<code class="classname">String</code>.</p>
</li>
<li>
<p>Complex objects that implement Java serialization.</p>
<p>Use this if you are storing objects that implement
<code class="classname">Serializable</code> and if you do not need to sort them.
</p>
</li>
<li>
<p>Non-serialized complex objects.</p>
<p>If you are storing objects that do not implement serialization,
you can create your own custom tuple bindings. Note that you should
use custom tuple bindings even if your objects are serializable if
you want to sort on that data.</p>
</li>
</ul>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="bindPrimitive"></a>Numerical and String Objects</h3>
</div>
</div>
</div>
<p>You can use the Bind APIs to store primitive data in a <code class="classname">DatabaseEntry</code>
object. That is, you can store a single field containing one of the following types:</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="classname">String</code>
</p>
</li>
<li>
<p>
<code class="classname">Character</code>
</p>
</li>
<li>
<p>
<code class="classname">Boolean</code>
</p>
</li>
<li>
<p>
<code class="classname">Byte</code>
</p>
</li>
<li>
<p>
<code class="classname">Short</code>
</p>
</li>
<li>
<p>
<code class="classname">Integer</code>
</p>
</li>
<li>
<p>
<code class="classname">Long</code>
</p>
</li>
<li>
<p>
<code class="classname">Float</code>
</p>
</li>
<li>
<p>
<code class="classname">Double</code>
</p>
</li>
</ul>
</div>
<p>
To store primitive data using the Bind APIs:
</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>Create an <code class="classname">EntryBinding</code> object.</p>
<p>When you do this, you use <code class="classname">TupleBinding.getPrimitiveBinding()</code>
to return an appropriate binding for the conversion.</p>
</li>
<li>
<p>Use the <code class="classname">EntryBinding</code> object to place
the numerical object on the <code class="classname">DatabaseEntry</code>.</p>
</li>
</ol>
</div>
<p>Once the data is stored in the DatabaseEntry, you can put it to
the database in whatever manner you wish. For example:</p>
<a id="java_dbt6"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.bind.EntryBinding;
import com.sleepycat.bind.tuple.TupleBinding;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseEntry;
...
Database myDatabase = null;
// Database open omitted for clarity.
// Need a key for the put.
try {
String aKey = "myLong";
DatabaseEntry theKey = new DatabaseEntry(aKey.getBytes("UTF-8"));
// Now build the DatabaseEntry using a TupleBinding
Long myLong = new Long(123456789l);
DatabaseEntry theData = new DatabaseEntry();
EntryBinding myBinding = TupleBinding.getPrimitiveBinding(Long.class);
myBinding.objectToEntry(myLong, theData);
// Now store it
myDatabase.put(null, theKey, theData);
} catch (Exception e) {
// Exception handling goes here
}</pre>
<p>Retrieval from the <code class="classname">DatabaseEntry</code> object is
performed in much the same way:</p>
<a id="java_dbt7"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.bind.EntryBinding;
import com.sleepycat.bind.tuple.TupleBinding;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;
...
Database myDatabase = null;
// Database open omitted for clarity
try {
// Need a key for the get
String aKey = "myLong";
DatabaseEntry theKey = new DatabaseEntry(aKey.getBytes("UTF-8"));
// Need a DatabaseEntry to hold the associated data.
DatabaseEntry theData = new DatabaseEntry();
// Bindings need only be created once for a given scope
EntryBinding myBinding = TupleBinding.getPrimitiveBinding(Long.class);
// Get it
OperationStatus retVal = myDatabase.get(null, theKey, theData,
LockMode.DEFAULT);
String retKey = null;
if (retVal == OperationStatus.SUCCESS) {
// Recreate the data.
// Use the binding to convert the byte array contained in theData
// to a Long type.
Long theLong = (Long) myBinding.entryToObject(theData);
retKey = new String(theKey.getData(), "UTF-8");
System.out.println("For key: '" + retKey + "' found Long: '" +
theLong + "'.");
} else {
System.out.println("No record found for key '" + retKey + "'.");
}
} catch (Exception e) {
// Exception handling goes here
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="object2dbt"></a>Serializable Complex Objects</h3>
</div>
</div>
</div>
<p>Frequently your application requires you to store and manage
objects for your record data and/or keys. You may need to do this if you
are caching objects created by another process. You may also want to do
this if you want to store multiple data values on a record. When used
with just primitive data, or with objects containing a single data member,
DB database records effectively represent a single row in a two-column table.
By storing a complex object in the record, you can turn each record into
a single row in an <span class="emphasis"><em>n</em></span>-column table, where
<span class="emphasis"><em>n</em></span> is the number of data members contained by the
stored object(s).</p>
<p>In order to store objects in a
DB database, you must convert them to and from a <code class="literal">byte</code> array.
The first instinct for many Java programmers is to do this using Java
serialization. While this is functionally a correct solution, the result
is poor space-performance because this causes the class information
to be stored on every such database record. This information can be quite large
and it is redundant — the class information does not vary for serialized objects of the same type.
</p>
<p>
In other words, directly using serialization to place your objects into byte
arrays means that you will be storing a great deal of unnecessary information in
your database, which ultimately leads to larger databases and more expensive disk
I/O.
</p>
<p>The easiest way for you to solve this problem is to use the Bind
APIs to perform the serialization for you. Doing so causes the extra
object information to be saved off to a unique <code class="classname">Database</code>
dedicated for that purpose. This means that you do not have to duplicate
that information on each record in the <code class="classname">Database</code>
that your application is using to store its information.</p>
<p>
Note that when you use the Bind APIs to perform serialization, you still
receive all the benefits of serialization. You can still use arbitrarily
complex object graphs, and you still receive built-in class evolution
through the serialVersionUID (SUID) scheme. All of the Java
serialization rules apply without modification. For example, you can
implement Externalizable instead of Serializable.
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="bindCaveats"></a>Usage Caveats</h4>
</div>
</div>
</div>
<p>Before using the Bind APIs to perform serialization, you may
want to consider writing your own custom tuple bindings. Specifically,
avoid serialization if:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
If you need to sort based on the objects your are storing.
The sort order is meaningless for the byte arrays that you
obtain through serialization. Consequently, you should not use serialization for keys if you
care about their sort order. You should
also not use serialization for record data if your
<code class="classname">Database</code> supports duplicate records and you care about sort order.
</p>
</li>
<li>
<p>
You want to minimize the size of your byte arrays. Even when using the Bind APIs to perform the
serialization the resulting <code class="literal">byte</code> array may be larger than necessary. You can achieve
more compact results by building your own custom tuple binding.
</p>
</li>
<li>
<p>
You want to optimize for speed. In general, custom tuple bindings are faster than serialization at
moving data in and out of <code class="literal">byte</code> arrays.
</p>
</li>
</ul>
</div>
<p>
For information on building your own custom tuple binding, see <a class="xref" href="bindAPI.html#customTuple" title="Custom Tuple Bindings">Custom Tuple Bindings</a>.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="objectSerial"></a>Serializing Objects</h4>
</div>
</div>
</div>
<p>To store a serializable complex object using the
Bind APIs:</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>
Implement java.io.Serializable in the class whose instances that
you want to store.
</p>
</li>
<li>
<p>Open (create) your databases. You need two. The first is the
database that you use to store your data. The second is used to
store the class information.</p>
</li>
<li>
<p>Instantiate a class catalog. You do this with
<code class="classname">com.sleepycat.bind.serial.StoredClassCatalog</code>,
and at that time you must provide a handle to an open database
that is used to store the class information.</p>
</li>
<li>
<p>Create an entry binding that uses <code class="methodname">com.sleepycat.bind.serial.SerialBinding</code>.</p>
</li>
<li>
<p>Instantiate an instance of the object that you want to
store, and place it in a <code class="classname">DatabaseEntry</code>
using the entry binding that you created in the previous step.</p>
</li>
</ol>
</div>
<p>
For example, suppose you want to store a long, double, and a
String as a record's data. Then you might create a class that
looks something like this:
</p>
<a id="java_dbt8"></a>
<pre class="programlisting">package db.GettingStarted;
import java.io.Serializable;
public class MyData implements Serializable {
private long longData;
private double doubleData;
private String description;
MyData() {
longData = 0;
doubleData = 0.0;
description = null;
}
public void setLong(long data) {
longData = data;
}
public void setDouble(double data) {
doubleData = data;
}
public void setDescription(String data) {
description = data;
}
public long getLong() {
return longData;
}
public double getDouble() {
return doubleData;
}
public String getDescription() {
return description;
}
}</pre>
<p>You can then store instances of this class as follows:</p>
<a id="java_dbt9"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.bind.EntryBinding;
import com.sleepycat.bind.serial.StoredClassCatalog;
import com.sleepycat.bind.serial.SerialBinding;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseType;
...
// The key data.
String aKey = "myData";
// The data data
MyData data2Store = new MyData();
data2Store.setLong(123456789l);
data2Store.setDouble(1234.9876543);
data2Store.setDescription("A test instance of this class");
try {
// Open the database that you will use to store your data
DatabaseConfig myDbConfig = new DatabaseConfig();
myDbConfig.setAllowCreate(true);
myDbConfig.setSortedDuplicates(true);
myDbConfig.setType(DatabaseType.BTREE);
Database myDatabase = new Database("myDb", null, myDbConfig);
// Open the database that you use to store your class information.
// The db used to store class information does not require duplicates
// support.
myDbConfig.setSortedDuplicates(false);
Database myClassDb = new Database("classDb", null, myDbConfig);
// Instantiate the class catalog
StoredClassCatalog classCatalog = new StoredClassCatalog(myClassDb);
// Create the binding
EntryBinding dataBinding = new SerialBinding(classCatalog,
MyData.class);
// Create the DatabaseEntry for the key
DatabaseEntry theKey = new DatabaseEntry(aKey.getBytes("UTF-8"));
// Create the DatabaseEntry for the data. Use the EntryBinding object
// that was just created to populate the DatabaseEntry
DatabaseEntry theData = new DatabaseEntry();
dataBinding.objectToEntry(data2Store, theData);
// Put it as normal
myDatabase.put(null, theKey, theData);
// Database and environment close omitted for brevity
} catch (Exception e) {
// Exception handling goes here
}</pre>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="objectDeserial"></a>Deserializing Objects</h4>
</div>
</div>
</div>
<p>Once an object is stored in the database, you can retrieve the
<code class="classname">MyData</code> objects from the retrieved
<code class="classname">DatabaseEntry</code> using the Bind APIs in much the
same way as is described above. For example:</p>
<a id="java_dbt10"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.bind.EntryBinding;
import com.sleepycat.bind.serial.StoredClassCatalog;
import com.sleepycat.bind.serial.SerialBinding;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseType;
import com.sleepycat.db.LockMode;
...
// The key data.
String aKey = "myData";
try {
// Open the database that stores your data
DatabaseConfig myDbConfig = new DatabaseConfig();
myDbConfig.setAllowCreate(false);
myDbConfig.setType(DatabaseType.BTREE);
Database myDatabase = new Database("myDb", null, myDbConfig);
// Open the database that stores your class information.
Database myClassDb = new Database("classDb", null, myDbConfig);
// Instantiate the class catalog
StoredClassCatalog classCatalog = new StoredClassCatalog(myClassDb);
// Create the binding
EntryBinding dataBinding = new SerialBinding(classCatalog,
MyData.class);
// Create DatabaseEntry objects for the key and data
DatabaseEntry theKey = new DatabaseEntry(aKey.getBytes("UTF-8"));
DatabaseEntry theData = new DatabaseEntry();
// Do the get as normal
myDatabase.get(null, theKey, theData, LockMode.DEFAULT);
// Recreate the MyData object from the retrieved DatabaseEntry using
// the EntryBinding created above
MyData retrievedData = (MyData) dataBinding.entryToObject(theData);
// Database and environment close omitted for brevity
} catch (Exception e) {
// Exception handling goes here
}</pre>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="customTuple"></a>Custom Tuple Bindings</h3>
</div>
</div>
</div>
<p>
If you want to store complex objects in your database, then you can use
tuple bindings to do this. While they are more work to write and
maintain than if you were to use serialization, the
<code class="literal">byte</code> array conversion is faster. In addition, custom
tuple bindings should allow you to create <code class="literal">byte</code> arrays
that are smaller than those created by serialization. Custom tuple
bindings also allow you to optimize your BTree comparisons, whereas
serialization does not.
</p>
<p>
For information on using serialization to store complex objects, see
<a class="xref" href="bindAPI.html#object2dbt" title="Serializable Complex Objects">Serializable Complex Objects</a>.
</p>
<p>To store complex objects using a custom tuple binding:</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>Implement the class whose instances that you want to store.
Note that you do not have to implement the Serializable interface.</p>
</li>
<li>
<p>Write a tuple binding using the <code class="classname">com.sleepycat.bind.tuple.TupleBinding</code>
class.</p>
</li>
<li>
<p>Open (create) your database. Unlike serialization, you only
need one.</p>
</li>
<li>
<p>Create an entry binding that uses the tuple binding that you
implemented in step 2.</p>
</li>
<li>
<p>Instantiate an instance of the object that you want to store,
and place it in a <code class="classname">DatabaseEntry</code> using the
entry binding that you created in the previous step.</p>
</li>
</ol>
</div>
<p>
For example, suppose you want to your keys to be instances of the
following class:
</p>
<a id="java_dbt11"></a>
<pre class="programlisting">package db.GettingStarted;
public class MyData2 {
private long longData;
private Double doubleData;
private String description;
public MyData2() {
longData = 0;
doubleData = new Double(0.0);
description = "";
}
public void setLong(long data) {
longData = data;
}
public void setDouble(Double data) {
doubleData = data;
}
public void setString(String data) {
description = data;
}
public long getLong() {
return longData;
}
public Double getDouble() {
return doubleData;
}
public String getString() {
return description;
}
} </pre>
<p>In this case, you need to write a tuple binding for the
<code class="classname">MyData2</code> class. When you do this, you must
implement the <code class="methodname">TupleBinding.objectToEntry()</code>
and <code class="methodname">TupleBinding.entryToObject()</code> abstract methods.
Remember the following as you implement these methods:</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>You use <code class="methodname">TupleBinding.objectToEntry()</code> to convert
objects to <code class="literal">byte</code> arrays. You use
<code class="classname">com.sleepycat.bind.tuple.TupleOutput</code> to write
primitive data types to the <code class="literal">byte</code> array. Note that
<code class="classname">TupleOutput</code> provides methods that allows
you to work with numerical types (<code class="literal">long</code>,
<code class="literal">double</code>, <code class="literal">int</code>, and so forth) and
not the corresponding <code class="literal">java.lang</code> numerical
classes.</p>
</li>
<li>
<p>The order that you write data to the <code class="literal">byte</code>
array in <code class="methodname">TupleBinding.objectToEntry()</code> is the order that
it appears in the array. So given the <code class="classname">MyData2</code>
class as an example, if you write <code class="literal">description</code>,
<code class="literal">doubleData</code>, and then <code class="literal">longData</code>,
then the resulting byte array will contain these data elements in
that order. This means that your records will sort based on the
value of the <code class="literal">description</code> data member and then
the <code class="literal">doubleData</code> member, and so forth. If you
prefer to sort based on, say, the <code class="literal">longData</code> data
member, write it to the byte array first.</p>
</li>
<li>
<p>You use <code class="methodname">TupleBinding.entryToObject()</code> to convert
the <code class="literal">byte</code> array back into an instance of your
original class. You use <code class="classname">com.sleepycat.bind.tuple.TupleInput</code>
to get data from the <code class="literal">byte</code> array.</p>
</li>
<li>
<p>The order that you read data from the <code class="literal">byte</code>
array must be exactly the same as the order in which it was written.</p>
</li>
</ul>
</div>
<p>For example:</p>
<a id="java_dbt12"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.bind.tuple.TupleBinding;
import com.sleepycat.bind.tuple.TupleInput;
import com.sleepycat.bind.tuple.TupleOutput;
public class MyTupleBinding extends TupleBinding {
// Write a MyData2 object to a TupleOutput
public void objectToEntry(Object object, TupleOutput to) {
MyData2 myData = (MyData2)object;
// Write the data to the TupleOutput (a DatabaseEntry).
// Order is important. The first data written will be
// the first bytes used by the default comparison routines.
to.writeDouble(myData.getDouble().doubleValue());
to.writeLong(myData.getLong());
to.writeString(myData.getString());
}
// Convert a TupleInput to a MyData2 object
public Object entryToObject(TupleInput ti) {
// Data must be read in the same order that it was
// originally written.
Double theDouble = new Double(ti.readDouble());
long theLong = ti.readLong();
String theString = ti.readString();
MyData2 myData = new MyData2();
myData.setDouble(theDouble);
myData.setLong(theLong);
myData.setString(theString);
return myData;
}
} </pre>
<p>In order to use the tuple binding, instantiate the binding and
then use:</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><code class="methodname">MyTupleBinding.objectToEntry()</code> to
convert a MyData2 object to a <code class="classname">DatabaseEntry</code>.</p>
</li>
<li>
<p><code class="methodname">MyTupleBinding.entryToObject()</code> to convert
a <code class="classname">DatabaseEntry</code> to a <code class="classname">MyData2</code>
object.</p>
</li>
</ul>
</div>
<p>For example:</p>
<a id="java_dbt13"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.bind.tuple.TupleBinding;
import com.sleepycat.db.DatabaseEntry;
...
TupleBinding keyBinding = new MyTupleBinding();
MyData2 theKeyData = new MyData2();
theKeyData.setLong(123456789l);
theKeyData.setDouble(new Double(12345.6789));
theKeyData.setString("My key data");
DatabaseEntry myKey = new DatabaseEntry();
try {
// Store theKeyData in the DatabaseEntry
keyBinding.objectToEntry(theKeyData, myKey);
...
// Database put and get activity omitted for clarity
...
// Retrieve the key data
theKeyData = (MyData2) keyBinding.entryToObject(myKey);
} catch (Exception e) {
// Exception handling goes here
}</pre>
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