diff --git a/src/main/java/com/alibaba/druid/filter/config/ConfigFilter.java b/src/main/java/com/alibaba/druid/filter/config/ConfigFilter.java
index cf6820566d..7f06391442 100644
--- a/src/main/java/com/alibaba/druid/filter/config/ConfigFilter.java
+++ b/src/main/java/com/alibaba/druid/filter/config/ConfigFilter.java
@@ -73,7 +73,7 @@ public class ConfigFilter extends FilterAdapter {
         return algorithm;
     }
 
-    public void setAlgorithm(String algorithm) {
+    public final void setAlgorithm(String algorithm) {
         this.algorithm = algorithm;
         try {
             this.cipher = Cipher.getInstance(algorithm);
@@ -86,7 +86,7 @@ public class ConfigFilter extends FilterAdapter {
         return encryptedPassword;
     }
 
-    public void setEncryptedPassword(String encryptedPassword) {
+    public final void setEncryptedPassword(String encryptedPassword) {
         this.encryptedPassword = encryptedPassword;
     }
 
@@ -94,7 +94,7 @@ public class ConfigFilter extends FilterAdapter {
         return key;
     }
 
-    public void setKey(String key) {
+    public final void setKey(String key) {
         this.key = key;
 
         byte[] bytes = Base64.base64ToByteArray(key);
diff --git a/src/main/java/com/alibaba/druid/filter/encoding/EncodingConvertFilter.java b/src/main/java/com/alibaba/druid/filter/encoding/EncodingConvertFilter.java
index 75af4b7979..97d8afb07b 100644
--- a/src/main/java/com/alibaba/druid/filter/encoding/EncodingConvertFilter.java
+++ b/src/main/java/com/alibaba/druid/filter/encoding/EncodingConvertFilter.java
@@ -233,7 +233,7 @@ public class EncodingConvertFilter extends FilterAdapter {
 
             return charsetConvert.encode(s);
         } catch (UnsupportedEncodingException e) {
-            throw new SQLException(e.getMessage());
+            throw new SQLException(e.getMessage(), e);
         }
     }
 
@@ -242,7 +242,7 @@ public class EncodingConvertFilter extends FilterAdapter {
             CharsetConvert charsetConvert = (CharsetConvert) connection.getAttributes().get(ATTR_CHARSET_CONVERTER);
             return charsetConvert.decode(s);
         } catch (UnsupportedEncodingException e) {
-            throw new SQLException(e.getMessage());
+            throw new SQLException(e.getMessage(), e);
         }
     }
 
diff --git a/src/main/java/com/alibaba/druid/proxy/DruidDriver.java b/src/main/java/com/alibaba/druid/proxy/DruidDriver.java
index 14e0fca618..2fe34a13cc 100644
--- a/src/main/java/com/alibaba/druid/proxy/DruidDriver.java
+++ b/src/main/java/com/alibaba/druid/proxy/DruidDriver.java
@@ -250,9 +250,9 @@ public class DruidDriver implements Driver, DruidDriverMBean {
         try {
             rawDriver = (Driver) rawDriverClass.newInstance();
         } catch (InstantiationException e) {
-            throw new SQLException("create driver instance error, driver className '" + className + "'");
+            throw new SQLException("create driver instance error, driver className '" + className + "'", e);
         } catch (IllegalAccessException e) {
-            throw new SQLException("create driver instance error, driver className '" + className + "'");
+            throw new SQLException("create driver instance error, driver className '" + className + "'", e);
         }
 
         return rawDriver;
diff --git a/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlExprParser.java b/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlExprParser.java
index ccec633f7f..4eecb8a673 100644
--- a/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlExprParser.java
+++ b/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlExprParser.java
@@ -317,8 +317,8 @@ public class MySqlExprParser extends SQLExprParser {
 
                         if (lexer.token() == Token.FOR) {
                             lexer.nextToken();
-                            SQLExpr _for = expr();
-                            methodInvokeExpr.putAttribute("FOR", _for);
+                            SQLExpr forExpr = expr();
+                            methodInvokeExpr.putAttribute("FOR", forExpr);
                         }
                         break;
                     } else if (lexer.token() == Token.RPAREN) {
diff --git a/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlStatementParser.java b/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlStatementParser.java
index d8593d197e..03fddc5806 100644
--- a/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlStatementParser.java
+++ b/src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlStatementParser.java
@@ -129,7 +129,22 @@ import com.alibaba.druid.sql.parser.Token;
 
 public class MySqlStatementParser extends SQLStatementParser {
 
-    private static final String RESET = "RESET";
+    private static final String COLLATE2     = "COLLATE";
+    private static final String CASCADE      = "CASCADE";
+    private static final String RESTRICT     = "RESTRICT";
+    private static final String CHAIN        = "CHAIN";
+    private static final String ENGINES      = "ENGINES";
+    private static final String ENGINE       = "ENGINE";
+    private static final String BINLOG       = "BINLOG";
+    private static final String EVENTS       = "EVENTS";
+    private static final String CHARACTER    = "CHARACTER";
+    private static final String SESSION      = "SESSION";
+    private static final String GLOBAL       = "GLOBAL";
+    private static final String VARIABLES    = "VARIABLES";
+    private static final String ERRORS       = "ERRORS";
+    private static final String STATUS       = "STATUS";
+    private static final String IGNORE       = "IGNORE";
+    private static final String RESET        = "RESET";
     private static final String DESCRIBE     = "DESCRIBE";
     private static final String DESC         = "DESC";
     private static final String WRITE        = "WRITE";
@@ -144,7 +159,7 @@ public class MySqlStatementParser extends SQLStatementParser {
     private static final String DELAYED      = "DELAYED";
     private static final String LOW_PRIORITY = "LOW_PRIORITY";
 
-    public MySqlStatementParser(String sql) {
+    public MySqlStatementParser(String sql){
         super(new MySqlExprParser(sql));
     }
 
@@ -172,7 +187,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 stmt.setLowPriority(true);
             }
 
-            if (identifierEquals("IGNORE")) {
+            if (identifierEquals(IGNORE)) {
                 lexer.nextToken();
                 stmt.setIgnore(true);
             }
@@ -235,7 +250,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 lexer.nextToken();
             }
 
-            if (identifierEquals("IGNORE")) {
+            if (identifierEquals(IGNORE)) {
                 deleteStatement.setIgnore(true);
                 lexer.nextToken();
             }
@@ -514,7 +529,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             return true;
         }
 
-        if (identifierEquals("BINLOG")) {
+        if (identifierEquals(BINLOG)) {
             SQLStatement stmt = parseBinlog();
             statementList.add(stmt);
             return true;
@@ -649,7 +664,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             accept(Token.STAR);
             accept(Token.RPAREN);
 
-            if (identifierEquals("ERRORS")) {
+            if (identifierEquals(ERRORS)) {
                 lexer.nextToken();
 
                 MySqlShowErrorsStatement stmt = new MySqlShowErrorsStatement();
@@ -666,7 +681,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             }
         }
 
-        if (identifierEquals("ERRORS")) {
+        if (identifierEquals(ERRORS)) {
             lexer.nextToken();
 
             MySqlShowErrorsStatement stmt = new MySqlShowErrorsStatement();
@@ -675,7 +690,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             return stmt;
         }
 
-        if (identifierEquals("STATUS")) {
+        if (identifierEquals(STATUS)) {
             lexer.nextToken();
 
             MySqlShowStatusStatement stmt = parseShowStatus();
@@ -683,7 +698,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             return stmt;
         }
 
-        if (identifierEquals("VARIABLES")) {
+        if (identifierEquals(VARIABLES)) {
             lexer.nextToken();
 
             MySqlShowVariantsStatement stmt = parseShowVariants();
@@ -691,17 +706,17 @@ public class MySqlStatementParser extends SQLStatementParser {
             return stmt;
         }
 
-        if (identifierEquals("GLOBAL")) {
+        if (identifierEquals(GLOBAL)) {
             lexer.nextToken();
 
-            if (identifierEquals("STATUS")) {
+            if (identifierEquals(STATUS)) {
                 lexer.nextToken();
                 MySqlShowStatusStatement stmt = parseShowStatus();
                 stmt.setGlobal(true);
                 return stmt;
             }
 
-            if (identifierEquals("VARIABLES")) {
+            if (identifierEquals(VARIABLES)) {
                 lexer.nextToken();
                 MySqlShowVariantsStatement stmt = parseShowVariants();
                 stmt.setGlobal(true);
@@ -709,17 +724,17 @@ public class MySqlStatementParser extends SQLStatementParser {
             }
         }
 
-        if (identifierEquals("SESSION")) {
+        if (identifierEquals(SESSION)) {
             lexer.nextToken();
 
-            if (identifierEquals("STATUS")) {
+            if (identifierEquals(STATUS)) {
                 lexer.nextToken();
                 MySqlShowStatusStatement stmt = parseShowStatus();
                 stmt.setSession(true);
                 return stmt;
             }
 
-            if (identifierEquals("VARIABLES")) {
+            if (identifierEquals(VARIABLES)) {
                 lexer.nextToken();
                 MySqlShowVariantsStatement stmt = parseShowVariants();
                 stmt.setSession(true);
@@ -749,11 +764,11 @@ public class MySqlStatementParser extends SQLStatementParser {
                 lexer.nextToken();
                 return new MySqlShowMasterLogsStatement();
             }
-            acceptIdentifier("STATUS");
+            acceptIdentifier(STATUS);
             return new MySqlShowMasterStatusStatement();
         }
 
-        if (identifierEquals("CHARACTER")) {
+        if (identifierEquals(CHARACTER)) {
             lexer.nextToken();
             accept(Token.SET);
             MySqlShowCharacterSetStatement stmt = new MySqlShowCharacterSetStatement();
@@ -788,9 +803,9 @@ public class MySqlStatementParser extends SQLStatementParser {
             return stmt;
         }
 
-        if (identifierEquals("BINLOG")) {
+        if (identifierEquals(BINLOG)) {
             lexer.nextToken();
-            acceptIdentifier("EVENTS");
+            acceptIdentifier(EVENTS);
             MySqlShowBinLogEventsStatement stmt = new MySqlShowBinLogEventsStatement();
 
             if (lexer.token() == Token.IN) {
@@ -875,7 +890,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             throw new ParserException("TODO " + lexer.stringVal());
         }
 
-        if (identifierEquals("ENGINE")) {
+        if (identifierEquals(ENGINE)) {
             lexer.nextToken();
             MySqlShowEngineStatement stmt = new MySqlShowEngineStatement();
             stmt.setName(this.exprParser.name());
@@ -886,19 +901,19 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         if (identifierEquals("STORAGE")) {
             lexer.nextToken();
-            acceptIdentifier("ENGINES");
+            acceptIdentifier(ENGINES);
             MySqlShowEnginesStatement stmt = new MySqlShowEnginesStatement();
             stmt.setStorage(true);
             return stmt;
         }
 
-        if (identifierEquals("ENGINES")) {
+        if (identifierEquals(ENGINES)) {
             lexer.nextToken();
             MySqlShowEnginesStatement stmt = new MySqlShowEnginesStatement();
             return stmt;
         }
 
-        if (identifierEquals("EVENTS")) {
+        if (identifierEquals(EVENTS)) {
             lexer.nextToken();
             MySqlShowEventsStatement stmt = new MySqlShowEventsStatement();
 
@@ -929,7 +944,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 return stmt;
             }
 
-            acceptIdentifier("STATUS");
+            acceptIdentifier(STATUS);
             MySqlShowFunctionStatusStatement stmt = new MySqlShowFunctionStatusStatement();
 
             if (lexer.token() == Token.LIKE) {
@@ -946,7 +961,7 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         // MySqlShowFunctionStatusStatement
 
-        if (identifierEquals("ENGINE")) {
+        if (identifierEquals(ENGINE)) {
             lexer.nextToken();
             MySqlShowEngineStatement stmt = new MySqlShowEngineStatement();
             stmt.setName(this.exprParser.name());
@@ -957,13 +972,13 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         if (identifierEquals("STORAGE")) {
             lexer.nextToken();
-            acceptIdentifier("ENGINES");
+            acceptIdentifier(ENGINES);
             MySqlShowEnginesStatement stmt = new MySqlShowEnginesStatement();
             stmt.setStorage(true);
             return stmt;
         }
 
-        if (identifierEquals("ENGINES")) {
+        if (identifierEquals(ENGINES)) {
             lexer.nextToken();
             MySqlShowEnginesStatement stmt = new MySqlShowEnginesStatement();
             return stmt;
@@ -1063,7 +1078,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 return stmt;
             }
 
-            acceptIdentifier("STATUS");
+            acceptIdentifier(STATUS);
             MySqlShowProcedureStatusStatement stmt = new MySqlShowProcedureStatusStatement();
 
             if (lexer.token() == Token.LIKE) {
@@ -1149,7 +1164,7 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         if (identifierEquals("RELAYLOG")) {
             lexer.nextToken();
-            acceptIdentifier("EVENTS");
+            acceptIdentifier(EVENTS);
             MySqlShowRelayLogEventsStatement stmt = new MySqlShowRelayLogEventsStatement();
 
             if (lexer.token() == Token.IN) {
@@ -1169,7 +1184,7 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         if (identifierEquals("RELAYLOG")) {
             lexer.nextToken();
-            acceptIdentifier("EVENTS");
+            acceptIdentifier(EVENTS);
             MySqlShowRelayLogEventsStatement stmt = new MySqlShowRelayLogEventsStatement();
 
             if (lexer.token() == Token.IN) {
@@ -1189,7 +1204,7 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         if (identifierEquals("SLAVE")) {
             lexer.nextToken();
-            if (identifierEquals("STATUS")) {
+            if (identifierEquals(STATUS)) {
                 lexer.nextToken();
                 return new MySqlShowSlaveStatusStatement();
             } else {
@@ -1201,7 +1216,7 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         if (lexer.token() == Token.TABLE) {
             lexer.nextToken();
-            acceptIdentifier("STATUS");
+            acceptIdentifier(STATUS);
             MySqlShowTableStatusStatement stmt = new MySqlShowTableStatusStatement();
             if (lexer.token() == Token.FROM || lexer.token() == Token.IN) {
                 lexer.nextToken();
@@ -1405,10 +1420,10 @@ public class MySqlStatementParser extends SQLStatementParser {
             lexer.nextToken();
             if (lexer.token() == Token.NOT) {
                 lexer.nextToken();
-                acceptIdentifier("CHAIN");
+                acceptIdentifier(CHAIN);
                 stmt.setChain(Boolean.FALSE);
             } else {
-                acceptIdentifier("CHAIN");
+                acceptIdentifier(CHAIN);
                 stmt.setChain(Boolean.TRUE);
             }
         }
@@ -1440,10 +1455,10 @@ public class MySqlStatementParser extends SQLStatementParser {
             lexer.nextToken();
             if (lexer.token() == Token.NOT) {
                 lexer.nextToken();
-                acceptIdentifier("CHAIN");
+                acceptIdentifier(CHAIN);
                 stmt.setChain(Boolean.FALSE);
             } else {
-                acceptIdentifier("CHAIN");
+                acceptIdentifier(CHAIN);
                 stmt.setChain(Boolean.TRUE);
             }
         }
@@ -1581,7 +1596,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             lexer.nextToken();
         }
 
-        if (identifierEquals("IGNORE")) {
+        if (identifierEquals(IGNORE)) {
             stmt.setIgnore(true);
             lexer.nextToken();
         }
@@ -1592,7 +1607,7 @@ public class MySqlStatementParser extends SQLStatementParser {
         SQLName tableName = exprParser.name();
         stmt.setTableName(tableName);
 
-        if (identifierEquals("CHARACTER")) {
+        if (identifierEquals(CHARACTER)) {
             lexer.nextToken();
             accept(Token.SET);
 
@@ -1613,7 +1628,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             stmt.setRowsIdentifiedBy(rowsIdentifiedBy);
         }
 
-        if (identifierEquals("IGNORE")) {
+        if (identifierEquals(IGNORE)) {
             throw new ParserException("TODO");
         }
 
@@ -1654,7 +1669,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             lexer.nextToken();
         }
 
-        if (identifierEquals("IGNORE")) {
+        if (identifierEquals(IGNORE)) {
             stmt.setIgnore(true);
             lexer.nextToken();
         }
@@ -1665,7 +1680,7 @@ public class MySqlStatementParser extends SQLStatementParser {
         SQLName tableName = exprParser.name();
         stmt.setTableName(tableName);
 
-        if (identifierEquals("CHARACTER")) {
+        if (identifierEquals(CHARACTER)) {
             lexer.nextToken();
             accept(Token.SET);
 
@@ -1686,7 +1701,7 @@ public class MySqlStatementParser extends SQLStatementParser {
             throw new ParserException("TODO");
         }
 
-        if (identifierEquals("IGNORE")) {
+        if (identifierEquals(IGNORE)) {
             throw new ParserException("TODO");
         }
 
@@ -1744,7 +1759,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 lexer.nextToken();
             }
 
-            if (identifierEquals("IGNORE")) {
+            if (identifierEquals(IGNORE)) {
                 insertStatement.setIgnore(true);
                 lexer.nextToken();
             }
@@ -1887,11 +1902,11 @@ public class MySqlStatementParser extends SQLStatementParser {
             break;
         }
 
-        if (identifierEquals("RESTRICT")) {
-            stmt.setOption("RESTRICT");
+        if (identifierEquals(RESTRICT)) {
+            stmt.setOption(RESTRICT);
             lexer.nextToken();
-        } else if (identifierEquals("CASCADE")) {
-            stmt.setOption("CASCADE");
+        } else if (identifierEquals(CASCADE)) {
+            stmt.setOption(CASCADE);
             lexer.nextToken();
         }
 
@@ -1923,11 +1938,11 @@ public class MySqlStatementParser extends SQLStatementParser {
             break;
         }
 
-        if (identifierEquals("RESTRICT")) {
-            stmt.setOption("RESTRICT");
+        if (identifierEquals(RESTRICT)) {
+            stmt.setOption(RESTRICT);
             lexer.nextToken();
-        } else if (identifierEquals("CASCADE")) {
-            stmt.setOption("CASCADE");
+        } else if (identifierEquals(CASCADE)) {
+            stmt.setOption(CASCADE);
             lexer.nextToken();
         }
 
@@ -1942,10 +1957,10 @@ public class MySqlStatementParser extends SQLStatementParser {
         accept(Token.SET);
 
         Boolean global = null;
-        if (identifierEquals("GLOBAL")) {
+        if (identifierEquals(GLOBAL)) {
             global = Boolean.TRUE;
             lexer.nextToken();
-        } else if (identifierEquals("SESSION")) {
+        } else if (identifierEquals(SESSION)) {
             global = Boolean.FALSE;
             lexer.nextToken();
         }
@@ -2003,7 +2018,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 String charSet = lexer.stringVal();
                 stmt.setCharSet(charSet);
                 lexer.nextToken();
-                if (identifierEquals("COLLATE")) {
+                if (identifierEquals(COLLATE2)) {
                     lexer.nextToken();
 
                     String collate = lexer.stringVal();
@@ -2012,7 +2027,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 }
             }
             return stmt;
-        } else if (identifierEquals("CHARACTER")) {
+        } else if (identifierEquals(CHARACTER)) {
             lexer.nextToken();
 
             accept(Token.SET);
@@ -2025,7 +2040,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                 String charSet = lexer.stringVal();
                 stmt.setCharSet(charSet);
                 lexer.nextToken();
-                if (identifierEquals("COLLATE")) {
+                if (identifierEquals(COLLATE2)) {
                     lexer.nextToken();
 
                     String collate = lexer.stringVal();
@@ -2057,7 +2072,7 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         boolean ignore = false;
 
-        if (identifierEquals("IGNORE")) {
+        if (identifierEquals(IGNORE)) {
             ignore = true;
             lexer.nextToken();
         }
@@ -2221,15 +2236,15 @@ public class MySqlStatementParser extends SQLStatementParser {
                     throw new ParserException("TODO " + lexer.token() + " " + lexer.stringVal());
                 } else if (identifierEquals("REMOVE")) {
                     throw new ParserException("TODO " + lexer.token() + " " + lexer.stringVal());
-                } else if (identifierEquals("ENGINE")) {
+                } else if (identifierEquals(ENGINE)) {
                     lexer.nextToken();
                     accept(Token.EQ);
-                    stmt.getItems().add(new MySqlAlterTableOption("ENGINE", lexer.stringVal()));
+                    stmt.getItems().add(new MySqlAlterTableOption(ENGINE, lexer.stringVal()));
                     lexer.nextToken();
-                } else if (identifierEquals("COLLATE")) {
+                } else if (identifierEquals(COLLATE2)) {
                     lexer.nextToken();
                     accept(Token.EQ);
-                    stmt.getItems().add(new MySqlAlterTableOption("COLLATE", lexer.stringVal()));
+                    stmt.getItems().add(new MySqlAlterTableOption(COLLATE2, lexer.stringVal()));
                     lexer.nextToken();
                 } else if (identifierEquals("PACK_KEYS")) {
                     lexer.nextToken();
@@ -2242,7 +2257,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                         stmt.getItems().add(new MySqlAlterTableOption("PACK_KEYS", lexer.stringVal()));
                         lexer.nextToken();
                     }
-                } else if (identifierEquals("CHARACTER")) {
+                } else if (identifierEquals(CHARACTER)) {
                     lexer.nextToken();
                     accept(Token.SET);
                     accept(Token.EQ);
@@ -2250,7 +2265,7 @@ public class MySqlStatementParser extends SQLStatementParser {
                     item.setCharacterSet(this.exprParser.primary());
                     if (lexer.token() == Token.COMMA) {
                         lexer.nextToken();
-                        acceptIdentifier("COLLATE");
+                        acceptIdentifier(COLLATE2);
                         accept(Token.EQ);
                         item.setCollate(this.exprParser.primary());
                     }
diff --git a/src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlOutputVisitor.java b/src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlOutputVisitor.java
index 50e65a8080..955bdb1ac6 100644
--- a/src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlOutputVisitor.java
+++ b/src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlOutputVisitor.java
@@ -544,10 +544,10 @@ public class MySqlOutputVisitor extends SQLASTOutputVisitor implements MySqlASTV
                 from.accept(this);
             }
 
-            SQLExpr _for = (SQLExpr) x.getAttribute("FOR");
-            if (_for != null) {
+            SQLExpr forExpr = (SQLExpr) x.getAttribute("FOR");
+            if (forExpr != null) {
                 print(" FOR ");
-                _for.accept(this);
+                forExpr.accept(this);
             }
             print(")");
 
diff --git a/src/main/java/com/alibaba/druid/sql/dialect/oracle/parser/OracleExprParser.java b/src/main/java/com/alibaba/druid/sql/dialect/oracle/parser/OracleExprParser.java
index d082300261..62d93a6e98 100644
--- a/src/main/java/com/alibaba/druid/sql/dialect/oracle/parser/OracleExprParser.java
+++ b/src/main/java/com/alibaba/druid/sql/dialect/oracle/parser/OracleExprParser.java
@@ -402,8 +402,8 @@ public class OracleExprParser extends SQLExprParser {
         }
         
         if (identifierEquals("AT")) {
-            char mark_ch = lexer.current();
-            int mark_bp = lexer.bp();
+            char markChar = lexer.current();
+            int markBp = lexer.bp();
             lexer.nextToken();
             if (lexer.token() == Token.LOCAL) {
                 lexer.nextToken();
@@ -412,7 +412,7 @@ public class OracleExprParser extends SQLExprParser {
                 if (identifierEquals("TIME")) {
                     lexer.nextToken();
                 } else {
-                    lexer.reset(mark_bp, mark_ch, Token.IDENTIFIER);
+                    lexer.reset(markBp, markChar, Token.IDENTIFIER);
                     return expr;
                 }
                 acceptIdentifier("ZONE");
diff --git a/src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java b/src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java
index ef49efdd07..d4317e3e32 100644
--- a/src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java
+++ b/src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java
@@ -499,20 +499,20 @@ public class SQLExprParser extends SQLParser {
         }
 
         if (expr instanceof SQLName || expr instanceof SQLDefaultExpr) {
-            String method_name;
+            String methodName;
 
             SQLMethodInvokeExpr methodInvokeExpr;
             if (expr instanceof SQLPropertyExpr) {
-                method_name = ((SQLPropertyExpr) expr).getName();
-                methodInvokeExpr = new SQLMethodInvokeExpr(method_name);
+                methodName = ((SQLPropertyExpr) expr).getName();
+                methodInvokeExpr = new SQLMethodInvokeExpr(methodName);
                 methodInvokeExpr.setOwner(((SQLPropertyExpr) expr).getOwner());
             } else {
-                method_name = expr.toString();
-                methodInvokeExpr = new SQLMethodInvokeExpr(method_name);
+                methodName = expr.toString();
+                methodInvokeExpr = new SQLMethodInvokeExpr(methodName);
             }
 
-            if (isAggreateFunction(method_name)) {
-                SQLAggregateExpr aggregateExpr = parseAggregateExpr(method_name);
+            if (isAggreateFunction(methodName)) {
+                SQLAggregateExpr aggregateExpr = parseAggregateExpr(methodName);
 
                 return aggregateExpr;
             }
@@ -664,10 +664,10 @@ public class SQLExprParser extends SQLParser {
     }
 
     public boolean isAggreateFunction(String word) {
-        String[] _aggregateFunctions = { "AVG", "COUNT", "MAX", "MIN", "STDDEV", "SUM" };
+        String[] aggregateFunctions = { "AVG", "COUNT", "MAX", "MIN", "STDDEV", "SUM" };
 
-        for (int i = 0; i < _aggregateFunctions.length; ++i) {
-            if (_aggregateFunctions[i].compareToIgnoreCase(word) == 0) {
+        for (int i = 0; i < aggregateFunctions.length; ++i) {
+            if (aggregateFunctions[i].compareToIgnoreCase(word) == 0) {
                 return true;
             }
         }
diff --git a/src/main/java/com/alibaba/druid/sql/parser/SQLStatementParser.java b/src/main/java/com/alibaba/druid/sql/parser/SQLStatementParser.java
index 3538278fb4..62a465e046 100644
--- a/src/main/java/com/alibaba/druid/sql/parser/SQLStatementParser.java
+++ b/src/main/java/com/alibaba/druid/sql/parser/SQLStatementParser.java
@@ -201,11 +201,11 @@ public class SQLStatementParser extends SQLParser {
             }
 
             if (lexer.token() == Token.LPAREN) {
-                char mark_ch = lexer.current();
-                int mark_bp = lexer.bp();
+                char markChar = lexer.current();
+                int markBp = lexer.bp();
                 lexer.nextToken();
                 if (lexer.token() == Token.SELECT) {
-                    lexer.reset(mark_bp, mark_ch, Token.LPAREN);
+                    lexer.reset(markBp, markChar, Token.LPAREN);
                     SQLStatement stmt = parseSelect();
                     statementList.add(stmt);
                     continue;
@@ -471,8 +471,8 @@ public class SQLStatementParser extends SQLParser {
     }
 
     public SQLStatement parseCreate() {
-        char mark_ch = lexer.current();
-        int mark_bp = lexer.bp();
+        char markChar = lexer.current();
+        int markBp = lexer.bp();
 
         accept(Token.CREATE);
 
@@ -489,7 +489,7 @@ public class SQLStatementParser extends SQLParser {
             lexer.nextToken();
             acceptIdentifier("REPLACE");
             if (lexer.token() == Token.PROCEDURE) {
-                lexer.reset(mark_bp, mark_ch, Token.CREATE);
+                lexer.reset(markBp, markChar, Token.CREATE);
                 return parseCreateProcedure();
             }
 
diff --git a/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java b/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java
index b43ae3d959..75c73975d0 100644
--- a/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java
+++ b/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java
@@ -299,7 +299,7 @@ public class SQLEvalVisitorUtils {
         try {
             return new SimpleDateFormat(format).parse(text);
         } catch (ParseException e) {
-            throw new DruidRuntimeException("format : " + format + ", value : " + text);
+            throw new DruidRuntimeException("format : " + format + ", value : " + text, e);
         }
     }
 
diff --git a/src/main/java/com/alibaba/druid/support/http/StatViewServlet.java b/src/main/java/com/alibaba/druid/support/http/StatViewServlet.java
index 61a105951c..2342ccb306 100644
--- a/src/main/java/com/alibaba/druid/support/http/StatViewServlet.java
+++ b/src/main/java/com/alibaba/druid/support/http/StatViewServlet.java
@@ -201,9 +201,9 @@ public class StatViewServlet extends HttpServlet {
         }
 
         if ("/submitLogin".equals(path)) {
-            String _username = request.getParameter(PARAM_NAME_USERNAME);
-            String _password = request.getParameter(PARAM_NAME_PASSWORD);
-            if (username.equals(_username) && password.equals(_password)) {
+            String usernameParam = request.getParameter(PARAM_NAME_USERNAME);
+            String passwordParam = request.getParameter(PARAM_NAME_PASSWORD);
+            if (username.equals(usernameParam) && password.equals(passwordParam)) {
                 request.getSession().setAttribute(SESSION_USER_KEY, username);
                 response.getWriter().print("success");
             } else {
diff --git a/src/main/java/com/alibaba/druid/support/http/stat/WebAppStat.java b/src/main/java/com/alibaba/druid/support/http/stat/WebAppStat.java
index 839e1ebae0..fef5588c3d 100644
--- a/src/main/java/com/alibaba/druid/support/http/stat/WebAppStat.java
+++ b/src/main/java/com/alibaba/druid/support/http/stat/WebAppStat.java
@@ -581,7 +581,7 @@ public class WebAppStat {
         }
 
         boolean isIE = userAgent.startsWith("MSIE", MOZILLA_COMPATIBLE_OFFSET);
-        int ie_prefix_index = 30; // "Mozilla/5.0 (compatible; MSIE ".length();
+        int iePrefixIndex = 30; // "Mozilla/5.0 (compatible; MSIE ".length();
 
         boolean isGoogleToolbar = false;
 
@@ -592,7 +592,7 @@ public class WebAppStat {
                 int tmp = userAgent.indexOf("IE ");
                 if (tmp != -1) {
                     isIE = true;
-                    ie_prefix_index = tmp + 3;
+                    iePrefixIndex = tmp + 3;
                 }
             }
         }
@@ -602,11 +602,11 @@ public class WebAppStat {
             browserIECount.incrementAndGet();
 
             char v1 = ' ', v2 = ' ';
-            if (userAgent.length() > ie_prefix_index + 1) {
-                v1 = userAgent.charAt(ie_prefix_index);
-                v2 = userAgent.charAt(ie_prefix_index + 1);
-            } else if (userAgent.length() > ie_prefix_index) {
-                v1 = userAgent.charAt(ie_prefix_index);
+            if (userAgent.length() > iePrefixIndex + 1) {
+                v1 = userAgent.charAt(iePrefixIndex);
+                v2 = userAgent.charAt(iePrefixIndex + 1);
+            } else if (userAgent.length() > iePrefixIndex) {
+                v1 = userAgent.charAt(iePrefixIndex);
             }
 
             switch (v1) {
diff --git a/src/main/java/com/alibaba/druid/support/http/util/IPAddress.java b/src/main/java/com/alibaba/druid/support/http/util/IPAddress.java
index cc7aee597f..fb406bdec2 100644
--- a/src/main/java/com/alibaba/druid/support/http/util/IPAddress.java
+++ b/src/main/java/com/alibaba/druid/support/http/util/IPAddress.java
@@ -262,9 +262,9 @@ public class IPAddress implements Cloneable {
                 throw new IllegalArgumentException("Invalid IP Address [" + ipAddressStr + "]");
             }
         } catch (NoSuchElementException ex) {
-            throw new IllegalArgumentException("Invalid IP Address [" + ipAddressStr + "]");
+            throw new IllegalArgumentException("Invalid IP Address [" + ipAddressStr + "]", ex);
         } catch (NumberFormatException ex) {
-            throw new IllegalArgumentException("Invalid IP Address [" + ipAddressStr + "]");
+            throw new IllegalArgumentException("Invalid IP Address [" + ipAddressStr + "]", ex);
         }
 
         return result;
diff --git a/src/main/java/com/alibaba/druid/support/http/util/IPRange.java b/src/main/java/com/alibaba/druid/support/http/util/IPRange.java
index 646085b7dd..bfb0ad9889 100644
--- a/src/main/java/com/alibaba/druid/support/http/util/IPRange.java
+++ b/src/main/java/com/alibaba/druid/support/http/util/IPRange.java
@@ -226,7 +226,7 @@ public class IPRange {
             // create the corresponding subnet decimal
             extendedNetworkPrefix = computeNetworkPrefixFromMask(ipSubnetMask);
             if (extendedNetworkPrefix == -1) {
-                throw new IllegalArgumentException("Invalid IP range [" + range + "]");
+                throw new IllegalArgumentException("Invalid IP range [" + range + "]", ex);
             }
         }
     }