improved sql parser export parameter sharding support.

src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlOutputVisitor.java

@@ -158,10 +158,9 @@ public class MySqlOutputVisitor extends SQLASTOutputVisitor implements MySqlASTV
 
     {
         this.dbType = JdbcConstants.MYSQL;
+        this.shardingSupport = true;
     }
 
-    private boolean shardingSupport = true;
-
     public MySqlOutputVisitor(Appendable appender){
         super(appender);
     }

src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java

@@ -57,6 +57,8 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter implements Paramet
     protected boolean parameterized = false;
     protected boolean parameterizedMergeInList = false;
 
+    protected boolean shardingSupport = false;
+
     public SQLASTOutputVisitor(Appendable appender){
         this.appender = appender;
     }
@@ -88,7 +90,7 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter implements Paramet
     }
 
     public void addTableMapping(String srcTable, String destTable) {
-        if (tableMapping != null) {
+        if (tableMapping == null) {
             tableMapping = new HashMap<String, String>();
         }
         tableMapping.put(srcTable, destTable);

src/test/java/com/alibaba/druid/bvt/sql/ExportParameterShardingTest.java

@@ -0,0 +1,63 @@
+package com.alibaba.druid.bvt.sql;
+
+import com.alibaba.druid.sql.SQLUtils;
+import com.alibaba.druid.sql.ast.SQLStatement;
+import com.alibaba.druid.sql.visitor.SQLASTOutputVisitor;
+import com.alibaba.druid.util.JdbcConstants;
+import com.alibaba.fastjson.JSON;
+import junit.framework.TestCase;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Created by wenshao on 23/11/2016.
+ */
+public class ExportParameterShardingTest extends TestCase {
+    String dbType = JdbcConstants.MYSQL;
+
+    public void test_exportParameter() throws Exception {
+        String sql = "select * from t_user_0000 where oid = 1001";
+
+        List<SQLStatement> stmtList = SQLUtils.parseStatements(sql, dbType);
+
+        assertEquals(1, stmtList.size());
+
+        SQLStatement stmt = stmtList.get(0);
+
+        StringBuilder out = new StringBuilder();
+        List<Object> parameters = new ArrayList<Object>();
+        SQLASTOutputVisitor visitor = SQLUtils.createOutputVisitor(out, dbType);
+        visitor.setParameterized(true);
+        visitor.setParameterizedMergeInList(true);
+        visitor.setParameters(parameters);
+
+        stmt.accept(visitor);
+
+        System.out.println(out);
+        System.out.println(JSON.toJSONString(parameters));
+
+        String restoredSql = restore(out.toString(), parameters);
+        assertEquals("SELECT *\n" +
+                "FROM t_user_0000\n" +
+                "WHERE oid = 1001", restoredSql);
+    }
+
+    public String restore(String sql, List<Object> parameters) {
+        List<SQLStatement> stmtList = SQLUtils.parseStatements(sql, dbType);
+
+        assertEquals(1, stmtList.size());
+
+        SQLStatement stmt = stmtList.get(0);
+
+        StringBuilder out = new StringBuilder();
+        SQLASTOutputVisitor visitor = SQLUtils.createOutputVisitor(out, dbType);
+        visitor.setParameters(parameters);
+
+        visitor.addTableMapping("t_user", "t_user_0000");
+
+        stmt.accept(visitor);
+
+        return out.toString();
+    }
+}