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<div class="title">Getting Started with the API in Java </div> </div>
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<div class="textblock"><p>WiredTiger applications will generally use the following classes to access and manage data:</p>
<ul>
<li>a Connection represents a connection to a database. Most applications will only open one connection to a database for each process. All methods in Connection are thread safe.</li>
<li>a Session represents a context in which database operations are performed. Sessions are opened on a specified connection, and applications must open a single session for each thread accessing the database.</li>
<li>a Cursor represents a cursor over a collection of data. Cursors are opened in the context of a session (which may have an associated transaction), and can query and update records. In the common case, a cursor is used to access records in a table. However, cursors can be used on subsets of tables (such as a single column or a projection of multiple columns), as an interface to statistics, configuration data or application-specific data sources.</li>
</ul>
<p>Handles and operations are <a class="el" href="config_strings_lang_java.html">configured using strings</a>, which keeps the set of methods in the API relatively small and makes the interface very similar regardless of the programming language used in the application. WiredTiger supports the C, C++, Java and Python programming languages (among others).</p>
<p>By default, WiredTiger works as a traditional key/value store, where the keys and values are raw byte arrays. Keys and values may be up to (4GB - 512B) bytes in size, but depending on how Session.create "maximum item sizes" are configured, large key and value items will be stored on overflow pages.</p>
<p>WiredTiger also supports a <a class="el" href="schema_lang_java.html">schema layer</a> so that keys and values types can be chosen from a list, or composite keys or values made up of columns with any combination of types. The size (4GB - 512B) byte limit on keys and values still applies.</p>
<p>All applications that use WiredTiger will be structured roughly as follows. The code below is taken from the complete example program ex_access.java.</p>
<h1><a class="anchor" id="basic_connection_lang_java"></a>
Connecting to a database</h1>
<p>To access a database, first open a connection and create a session handle for the single thread accessing the database:</p>
<div class="fragment"><div class="line"> Connection conn;</div><div class="line"> Session s;</div><div class="line"> Cursor c;</div><div class="line"></div><div class="line"> <span class="keywordflow">try</span> {</div><div class="line"> conn = wiredtiger.open(<span class="stringliteral">"WT_HOME"</span>, <span class="stringliteral">"create"</span>);</div><div class="line"> s = conn.<a class="code" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html#adad5965cd4a60f65b5ac01f7ca6d1fc0">open_session</a>(null);</div><div class="line"> } <span class="keywordflow">catch</span> (WiredTigerException wte) {</div><div class="line"> System.err.println(<span class="stringliteral">"WiredTigerException: "</span> + wte);</div><div class="line"> <span class="keywordflow">return</span>;</div><div class="line"> }</div></div><!-- fragment --><p> The configuration string <code>"create"</code> is passed to <code>wiredtiger.open</code> to indicate the database should be created if it does not already exist.</p>
<p>The code block above also shows simple error handling by catching WiredTigerException.</p>
<h1><a class="anchor" id="basic_create_table_lang_java"></a>
Creating a table</h1>
<p>Create a table we can use to store data:</p>
<div class="fragment"><div class="line"> s.create(<span class="stringliteral">"table:t"</span>, <span class="stringliteral">"key_format=S,value_format=u"</span>);</div></div><!-- fragment --><p> This call creates a table called <code>"access"</code>, configured to use strings for its key and value columns. (See <a class="el" href="schema_lang_java.html">Schema, Columns, Column Groups, Indices and Projections in Java</a> for more information on tables with other types of key and value columns.)</p>
<h1><a class="anchor" id="basic_cursors_lang_java"></a>
Accessing data with cursors</h1>
<p>Now that we have a table, we open a cursor to perform some operations on it:</p>
<div class="fragment"><div class="line"> c = s.open_cursor(<span class="stringliteral">"table:t"</span>, null, null);</div></div><!-- fragment --><p> Here, the string <code>"table:access"</code> specifies that we are opening the cursor on the table named <code>"access"</code>.</p>
<p>Then we insert a new row into the table. The Cursor.set_key and Cursor.set_value calls put the application's key and value into the cursor, respectively. The Cursor.insert call creates a record containing that value and inserts it into the table.</p>
<div class="fragment"><div class="line"> <span class="keywordflow">try</span> {</div><div class="line"> c.putKeyString(<span class="stringliteral">"foo"</span>);</div><div class="line"> c.putValueByteArray(<span class="stringliteral">"bar"</span>.getBytes());</div><div class="line"> c.insert();</div><div class="line"> } <span class="keywordflow">catch</span> (WiredTigerPackingException wtpe) {</div><div class="line"> System.err.println(<span class="stringliteral">"WiredTigerPackingException: "</span> + wtpe);</div><div class="line"> } <span class="keywordflow">catch</span> (WiredTigerException wte) {</div><div class="line"> System.err.println(<span class="stringliteral">"WiredTigerException: "</span> + wte);</div><div class="line"> }</div></div><!-- fragment --><p> Now we iterate through all of the records in the table, printing them out as we go:</p>
<div class="fragment"><div class="line"> <span class="keywordflow">try</span> {</div><div class="line"> c.reset();</div><div class="line"> <span class="keywordflow">while</span> (c.next() == 0) {</div><div class="line"> System.out.println(<span class="stringliteral">"Got: "</span> + c.getKeyString());</div><div class="line"> }</div><div class="line"> } <span class="keywordflow">catch</span> (WiredTigerPackingException wtpe) {</div><div class="line"> System.err.println(<span class="stringliteral">"WiredTigerPackingException: "</span> + wtpe);</div><div class="line"> } <span class="keywordflow">catch</span> (WiredTigerException wte) {</div><div class="line"> System.err.println(<span class="stringliteral">"WiredTigerException: "</span> + wte);</div><div class="line"> }</div></div><!-- fragment --><p> Note that the key and value parts of the records are returned as C strings because the table was created that way (even if it was created by a previous run of the example). No data extraction or conversion is required in the application.</p>
<p>Because the cursor was positioned in the table after the Cursor.insert call, we had to re-position it using the Cursor.reset call; if we weren't using the cursor for the call to Cursor.insert above, this loop would simplify to:</p>
<div class="fragment"><div class="line"><span class="keywordflow">while</span> ((ret = cursor-><a class="code" href="struct_w_t___c_u_r_s_o_r.html#a0503f16bd8f3d05aa3552f229b3a8e1b">next</a>(cursor)) == 0) {</div><div class="line"> ...</div><div class="line">}</div></div><!-- fragment --><h1><a class="anchor" id="basic_close_lang_java"></a>
Closing handles</h1>
<p>Lastly, we close the connection, which implicitly closes the cursor and session handles:</p>
<div class="fragment"><div class="line"> <span class="keywordflow">try</span> {</div><div class="line"> conn.close(null);</div><div class="line"> } <span class="keywordflow">catch</span> (WiredTigerException wte) {</div><div class="line"> System.err.println(<span class="stringliteral">"WiredTigerException: "</span> + wte);</div><div class="line"> }</div></div><!-- fragment --></div></div><!-- contents -->
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