bug fixed for DruidPooledStatement trace ResultSet, fix #4254

src/main/java/com/alibaba/druid/pool/DruidPooledStatement.java

@@ -55,7 +55,19 @@ public class DruidPooledStatement extends PoolableWrapper implements Statement {
     protected void addResultSetTrace(ResultSet resultSet) {
         if (resultSetTrace == null) {
             resultSetTrace = new ArrayList<ResultSet>(1);
+        } else if (resultSetTrace.size() > 0) {
+            int lastIndex = resultSetTrace.size() - 1;
+            ResultSet lastResultSet = resultSetTrace.get(lastIndex);
+            try {
+                if (lastResultSet.isClosed()) {
+                    resultSetTrace.set(lastIndex, resultSet);
+                    return;
+                }
+            } catch (SQLException ex) {
+                // skip
+            }
         }
+
         resultSetTrace.add(resultSet);
     }
 

src/test/java/com/alibaba/druid/bvt/pool/basic/PoolableCallableStatementTest.java

@@ -17,16 +17,7 @@ package com.alibaba.druid.bvt.pool.basic;
 
 import java.io.InputStream;
 import java.io.Reader;
-import java.sql.Blob;
-import java.sql.Clob;
-import java.sql.Date;
-import java.sql.NClob;
-import java.sql.RowId;
-import java.sql.SQLException;
-import java.sql.SQLXML;
-import java.sql.Time;
-import java.sql.Timestamp;
-import java.sql.Types;
+import java.sql.*;
 
 import org.junit.Assert;
 import junit.framework.TestCase;
@@ -73,6 +64,13 @@ public class PoolableCallableStatementTest extends TestCase {
         Assert.assertEquals(2, raw.getOutParameters().size());
     }
 
+    public void test_executeQuery_large() throws Exception {
+        for (int i = 0; i < 1000 * 1000; ++i) {
+            ResultSet rs = stmt.executeQuery();
+            rs.close();
+        }
+    }
+
     public void test_basic() throws Exception {
         Assert.assertEquals(raw, stmt.getCallableStatementRaw());
     }