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Lu, Huayi e6fa411af0 DWS DEV 830.201 version 
Reviewed-by: Pruthi, Vineet <vineet.pruthi@t-systems.com>
Co-authored-by: Lu, Huayi <luhuayi@huawei.com>
Co-committed-by: Lu, Huayi <luhuayi@huawei.com>
2024-05-16 07:24:04 +00:00

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<a name="EN-US_TOPIC_0000001233563135"></a><a name="EN-US_TOPIC_0000001233563135"></a>
<h1 class="topictitle1">Example: Common Operations</h1>
<div id="body8662426"><div class="section" id="EN-US_TOPIC_0000001233563135__section8820452474"><h4 class="sectiontitle">Example 1</h4><p id="EN-US_TOPIC_0000001233563135__p6320181125511">Before completing the following example, you need to create a stored procedure.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233563135__s9dfd0fc5586d464ebdf741ac5a35b8fc"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
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<span class="p">(</span>
<span class="w"> </span><span class="n">psv_in1</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="nb">integer</span><span class="p">,</span>
<span class="w"> </span><span class="n">psv_in2</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="nb">integer</span><span class="p">,</span>
<span class="w"> </span><span class="n">psv_inout</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="k">out</span><span class="w"> </span><span class="nb">integer</span>
<span class="p">)</span>
<span class="k">as</span>
<span class="k">begin</span>
<span class="w"> </span><span class="n">psv_inout</span><span class="w"> </span><span class="p">:</span><span class="o">=</span><span class="w"> </span><span class="n">psv_in1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">psv_in2</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">psv_inout</span><span class="p">;</span>
<span class="k">end</span><span class="p">;</span>
<span class="o">/</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001233563135__a576944990d75455893aebb8e8f175b6f">This example illustrates how to develop applications based on the <span id="EN-US_TOPIC_0000001233563135__text1800809317">GaussDB(DWS)</span> JDBC interface.</p>
<div class="codecoloring" codetype="Java" id="EN-US_TOPIC_0000001233563135__s745314d7b40b42dd99a0c2b182cf2b67"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
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<span class="normal">168</span></pre></div></td><td class="code"><div><pre><span></span><span class="c1">//DBtest.java</span>
<span class="c1">//gsjdbc4.jar is used as an example.</span>
<span class="c1">// This example illustrates the main processes of JDBC-based development, covering database connection creation, table creation, and data insertion.</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">java.sql.Connection</span><span class="p">;</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">java.sql.DriverManager</span><span class="p">;</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">java.sql.PreparedStatement</span><span class="p">;</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">java.sql.SQLException</span><span class="p">;</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">java.sql.Statement</span><span class="p">;</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">java.sql.CallableStatement</span><span class="p">;</span>
<span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">DBTest</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">//Establish a connection to the database.</span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="n">Connection</span><span class="w"> </span><span class="nf">GetConnection</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">username</span><span class="p">,</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">passwd</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">driver</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;org.postgresql.Driver&quot;</span><span class="p">;</span>
<span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">sourceURL</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;jdbc:postgresql://localhost:/gaussdb&quot;</span><span class="p">;</span>
<span class="w"> </span><span class="n">Connection</span><span class="w"> </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">null</span><span class="p">;</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">//Load the database driver.</span>
<span class="w"> </span><span class="n">Class</span><span class="p">.</span><span class="na">forName</span><span class="p">(</span><span class="n">driver</span><span class="p">).</span><span class="na">newInstance</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">Exception</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="kc">null</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">//Establish a connection to the database.</span>
<span class="w"> </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">DriverManager</span><span class="p">.</span><span class="na">getConnection</span><span class="p">(</span><span class="n">sourceURL</span><span class="p">,</span><span class="w"> </span><span class="n">username</span><span class="p">,</span><span class="w"> </span><span class="n">passwd</span><span class="p">);</span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Connection succeed!&quot;</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">Exception</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="kc">null</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">conn</span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="c1">//Run an ordinary SQL statement. Create a customer_t1 table.</span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">CreateTable</span><span class="p">(</span><span class="n">Connection</span><span class="w"> </span><span class="n">conn</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">Statement</span><span class="w"> </span><span class="n">stmt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">null</span><span class="p">;</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">stmt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="na">createStatement</span><span class="p">();</span>
<span class="w"> </span><span class="c1">//Run an ordinary SQL statement.</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">stmt</span>
<span class="w"> </span><span class="p">.</span><span class="na">executeUpdate</span><span class="p">(</span><span class="s">&quot;CREATE TABLE customer_t1(c_customer_sk INTEGER, c_customer_name VARCHAR(32));&quot;</span><span class="p">);</span>
<span class="w"> </span><span class="n">stmt</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">stmt</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">null</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">stmt</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">e1</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">//Run the preprocessing statement to insert data in batches.</span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">BatchInsertData</span><span class="p">(</span><span class="n">Connection</span><span class="w"> </span><span class="n">conn</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">PreparedStatement</span><span class="w"> </span><span class="n">pst</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">null</span><span class="p">;</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">//Generate a prepared statement.</span>
<span class="w"> </span><span class="n">pst</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="na">prepareStatement</span><span class="p">(</span><span class="s">&quot;INSERT INTO customer_t1 VALUES (?,?)&quot;</span><span class="p">);</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">//Add parameters.</span>
<span class="w"> </span><span class="n">pst</span><span class="p">.</span><span class="na">setInt</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="p">);</span>
<span class="w"> </span><span class="n">pst</span><span class="p">.</span><span class="na">setString</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;data &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">i</span><span class="p">);</span>
<span class="w"> </span><span class="n">pst</span><span class="p">.</span><span class="na">addBatch</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">//Run batch processing.</span>
<span class="w"> </span><span class="n">pst</span><span class="p">.</span><span class="na">executeBatch</span><span class="p">();</span>
<span class="w"> </span><span class="n">pst</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">pst</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">null</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pst</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">e1</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">//Run the precompilation statement to update data.</span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">ExecPreparedSQL</span><span class="p">(</span><span class="n">Connection</span><span class="w"> </span><span class="n">conn</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">PreparedStatement</span><span class="w"> </span><span class="n">pstmt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">null</span><span class="p">;</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pstmt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">conn</span>
<span class="w"> </span><span class="p">.</span><span class="na">prepareStatement</span><span class="p">(</span><span class="s">&quot;UPDATE customer_t1 SET c_customer_name = ? WHERE c_customer_sk = 1&quot;</span><span class="p">);</span>
<span class="w"> </span><span class="n">pstmt</span><span class="p">.</span><span class="na">setString</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;new Data&quot;</span><span class="p">);</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rowcount</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">pstmt</span><span class="p">.</span><span class="na">executeUpdate</span><span class="p">();</span>
<span class="w"> </span><span class="n">pstmt</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">pstmt</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">null</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pstmt</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">e1</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="c1">//Run a stored procedure.</span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">ExecCallableSQL</span><span class="p">(</span><span class="n">Connection</span><span class="w"> </span><span class="n">conn</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">CallableStatement</span><span class="w"> </span><span class="n">cstmt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">null</span><span class="p">;</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span>
<span class="w"> </span><span class="n">cstmt</span><span class="o">=</span><span class="n">conn</span><span class="p">.</span><span class="na">prepareCall</span><span class="p">(</span><span class="s">&quot;{? = CALL TESTPROC(?,?,?)}&quot;</span><span class="p">);</span>
<span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">setInt</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">50</span><span class="p">);</span><span class="w"> </span>
<span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">setInt</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">20</span><span class="p">);</span>
<span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">setInt</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">90</span><span class="p">);</span>
<span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">registerOutParameter</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">Types</span><span class="p">.</span><span class="na">INTEGER</span><span class="p">);</span><span class="w"> </span><span class="c1">//Register an OUT parameter as an integer.</span>
<span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">execute</span><span class="p">();</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">getInt</span><span class="p">(</span><span class="mi">4</span><span class="p">);</span><span class="w"> </span><span class="c1">//Obtain the out parameter value.</span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;The CallableStatment TESTPROC returns:&quot;</span><span class="o">+</span><span class="n">out</span><span class="p">);</span>
<span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">cstmt</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">null</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">cstmt</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">e1</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span>
<span class="w"> </span><span class="cm">/**</span>
<span class="cm"> * Main process. Call static methods one by one.</span>
<span class="cm"> * @param args</span>
<span class="cm"> */</span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">//Establish a connection to the database.</span>
<span class="w"> </span><span class="n">Connection</span><span class="w"> </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">GetConnection</span><span class="p">(</span><span class="s">&quot;tester&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;password&quot;</span><span class="p">);</span>
<span class="w"> </span><span class="c1">//Create a table.</span>
<span class="w"> </span><span class="n">CreateTable</span><span class="p">(</span><span class="n">conn</span><span class="p">);</span>
<span class="w"> </span><span class="c1">//Insert data in batches.</span>
<span class="w"> </span><span class="n">BatchInsertData</span><span class="p">(</span><span class="n">conn</span><span class="p">);</span>
<span class="w"> </span><span class="c1">//Run the precompilation statement to update data.</span>
<span class="w"> </span><span class="n">ExecPreparedSQL</span><span class="p">(</span><span class="n">conn</span><span class="p">);</span>
<span class="w"> </span><span class="c1">//Run a stored procedure.</span>
<span class="w"> </span><span class="n">ExecCallableSQL</span><span class="p">(</span><span class="n">conn</span><span class="p">);</span>
<span class="w"> </span><span class="c1">//Close the connection to the database.</span>
<span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">SQLException</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="na">printStackTrace</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">}</span>
</pre></div></td></tr></table></div>
</div>
</div>
<div class="section" id="EN-US_TOPIC_0000001233563135__section112115111092"><h4 class="sectiontitle">Example 2: High Client Memory Usage</h4><p id="EN-US_TOPIC_0000001233563135__p13961185014617">In this example, <strong id="EN-US_TOPIC_0000001233563135__b842352706155628">setFetchSize</strong> adjusts the memory usage of the client by using the database cursor to obtain server data in batches. It may increase network interaction and damage some performance.</p>
<p id="EN-US_TOPIC_0000001233563135__p28831955345">The cursor is valid within a transaction. Therefore, you need to disable the autocommit function.</p>
<div class="codecoloring" codetype="Java" id="EN-US_TOPIC_0000001233563135__screen14336113936"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span></pre></div></td><td class="code"><div><pre><span></span><span class="c1">// Disable the autocommit function.</span>
<span class="n">conn</span><span class="p">.</span><span class="na">setAutoCommit</span><span class="p">(</span><span class="kc">false</span><span class="p">);</span>
<span class="n">Statement</span><span class="w"> </span><span class="n">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="na">createStatement</span><span class="p">();</span>
<span class="c1">// Open the cursor and obtain 50 lines of data each time.</span>
<span class="n">st</span><span class="p">.</span><span class="na">setFetchSize</span><span class="p">(</span><span class="mi">50</span><span class="p">);</span>
<span class="n">ResultSet</span><span class="w"> </span><span class="n">rs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">st</span><span class="p">.</span><span class="na">executeQuery</span><span class="p">(</span><span class="s">&quot;SELECT * FROM mytable&quot;</span><span class="p">);</span>
<span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="n">rs</span><span class="p">.</span><span class="na">next</span><span class="p">()){</span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">print</span><span class="p">(</span><span class="s">&quot;a row was returned.&quot;</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">rs</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="c1">// Disable the server cursor.</span>
<span class="n">st</span><span class="p">.</span><span class="na">setFetchSize</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="n">rs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">st</span><span class="p">.</span><span class="na">executeQuery</span><span class="p">(</span><span class="s">&quot;SELECT * FROM mytable&quot;</span><span class="p">);</span>
<span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="n">rs</span><span class="p">.</span><span class="na">next</span><span class="p">()){</span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">print</span><span class="p">(</span><span class="s">&quot;many rows were returned.&quot;</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">rs</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
<span class="c1">// Close the statement.</span>
<span class="n">st</span><span class="p">.</span><span class="na">close</span><span class="p">();</span>
</pre></div></td></tr></table></div>
</div>
</div>
</div>
<div>
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<div class="parentlink"><strong>Parent topic:</strong> <a href="dws_04_0088.html">JDBC-Based Development</a></div>
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