Reduced unnecessary calls to Connection#setTransactionIsolation(level) in LocalTransaction (#1121)

* Reduced unnecessary calls to Connection#setTransactionIsolation(level) in LocalTransaction.

* Represent the absence of an isolation level to preserve with null

* Remove redundant suppression

Author: nakamura-to

doma-core/src/main/java/org/seasar/doma/jdbc/tx/LocalTransaction.java

@@ -133,21 +133,25 @@ protected void beginInternal(
         () -> {
           Connection connection = JdbcUtil.getConnection(dataSource);
 
-          int transactionIsolation;
-          try {
-            transactionIsolation = connection.getTransactionIsolation();
-          } catch (SQLException e) {
-            closeConnection(connection);
-            throw new JdbcException(Message.DOMA2056, e, e);
-          }
+          @SuppressWarnings("ReassignedVariable")
+          Integer currentTransactionIsolation = null;
           if (transactionIsolationLevel != null
               && transactionIsolationLevel != TransactionIsolationLevel.DEFAULT) {
-            int level = transactionIsolationLevel.getLevel();
             try {
-              connection.setTransactionIsolation(level);
+              currentTransactionIsolation = connection.getTransactionIsolation();
             } catch (SQLException e) {
               closeConnection(connection);
-              throw new JdbcException(Message.DOMA2055, e, transactionIsolationLevel.name(), e);
+              throw new JdbcException(Message.DOMA2056, e, e);
+            }
+            int level = transactionIsolationLevel.getLevel();
+            if (currentTransactionIsolation != level) {
+              try {
+                //noinspection MagicConstant
+                connection.setTransactionIsolation(level);
+              } catch (SQLException e) {
+                closeConnection(connection);
+                throw new JdbcException(Message.DOMA2055, e, transactionIsolationLevel.name(), e);
+              }
             }
           }
 
@@ -167,7 +171,8 @@ protected void beginInternal(
             }
           }
 
-          return new LocalTransactionConnection(connection, transactionIsolation, isAutoCommit);
+          return new LocalTransactionConnection(
+              connection, currentTransactionIsolation, isAutoCommit);
         });
     jdbcLogger.logTransactionBegun(className, callerMethodName, context.getId());
   }
@@ -422,9 +427,10 @@ protected void release(LocalTransactionContext context, String callerMethodName)
     LocalTransactionConnection localTransactionConnection = context.getConnection();
     Connection connection = localTransactionConnection.getWrappedConnection();
 
-    int isolationLevel = localTransactionConnection.getPreservedTransactionIsolation();
-    if (isolationLevel != Connection.TRANSACTION_NONE) {
+    Integer isolationLevel = localTransactionConnection.getPreservedTransactionIsolation();
+    if (isolationLevel != null && isolationLevel != Connection.TRANSACTION_NONE) {
       try {
+        //noinspection MagicConstant
         connection.setTransactionIsolation(isolationLevel);
       } catch (SQLException e) {
         jdbcLogger.logTransactionIsolationSettingFailure(

doma-core/src/main/java/org/seasar/doma/jdbc/tx/LocalTransactionConnection.java

@@ -19,7 +19,7 @@ class LocalTransactionConnection implements Connection {
 
   private final Connection connection;
 
-  private final int preservedTransactionIsolation;
+  private final Integer preservedTransactionIsolation;
 
   private final boolean preservedAutoCommitState;
 
@@ -31,15 +31,17 @@ class LocalTransactionConnection implements Connection {
    * @param preservedAutoCommitState the auto commit state to be preserved
    */
   public LocalTransactionConnection(
-      Connection connection, int preservedTransactionIsolation, boolean preservedAutoCommitState) {
+      Connection connection,
+      Integer preservedTransactionIsolation,
+      boolean preservedAutoCommitState) {
     assertNotNull(connection);
     assertTrue(!(connection instanceof LocalTransactionConnection));
     this.connection = connection;
     this.preservedTransactionIsolation = preservedTransactionIsolation;
     this.preservedAutoCommitState = preservedAutoCommitState;
   }
 
-  protected int getPreservedTransactionIsolation() {
+  protected Integer getPreservedTransactionIsolation() {
     return this.preservedTransactionIsolation;
   }
 
@@ -150,7 +152,6 @@ public DatabaseMetaData getMetaData() throws SQLException {
 
   @Override
   public int getTransactionIsolation() throws SQLException {
-    //noinspection MagicConstant
     return connection.getTransactionIsolation();
   }
 

doma-core/src/test/java/org/seasar/doma/jdbc/tx/KeepAliveLocalTransactionTest.java

@@ -106,7 +106,7 @@ public void setTransactionIsolation(int level) throws SQLException {
         new LocalTransactionDataSource(new MockDataSource(connection));
     LocalTransaction transaction = dataSource.getKeepAliveLocalTransaction(jdbcLogger);
     try {
-      transaction.begin(TransactionIsolationLevel.READ_COMMITTED);
+      transaction.begin(TransactionIsolationLevel.SERIALIZABLE);
       dataSource.getConnection();
       fail();
     } catch (JdbcException expected) {

doma-core/src/test/java/org/seasar/doma/jdbc/tx/LocalTransactionTest.java

@@ -105,7 +105,7 @@ public void setTransactionIsolation(int level) throws SQLException {
     LocalTransaction transaction = dataSource.getLocalTransaction(jdbcLogger);
 
     try {
-      transaction.begin(TransactionIsolationLevel.READ_COMMITTED);
+      transaction.begin(TransactionIsolationLevel.SERIALIZABLE);
       dataSource.getConnection();
       fail();
     } catch (JdbcException expected) {