add mapping support

src/main/java/com/alibaba/druid/mapping/MappingEngine.java

@@ -2,17 +2,14 @@ package com.alibaba.druid.mapping;
 
 import java.util.LinkedHashMap;
 
-import com.alibaba.druid.sql.SQLUtils;
-import com.alibaba.druid.sql.ast.expr.SQLNumberExpr;
-import com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock;
-import com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock.Limit;
-import com.alibaba.druid.sql.dialect.mysql.parser.MySqlSelectParser;
-import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
+import com.alibaba.druid.sql.visitor.SQLASTOutputVisitor;
 
 public class MappingEngine {
 
     private LinkedHashMap<String, Entity> entities = new LinkedHashMap<String, Entity>();
     private Integer                       maxLimit;
+    private MappingProvider               provider;
 
     public Integer getMaxLimit() {
         return maxLimit;
@@ -30,36 +27,23 @@ public class MappingEngine {
         this.entities.put(entity.getName(), entity);
     }
 
-    public SQLASTVisitor createMySqlMappingVisitor() {
-        return new MySqlMappingVisitor(entities);
+    public MappingVisitor createMappingVisitor() {
+        return provider.createMappingVisitor(this);
     }
 
-    public String explainToMySql(String sql) {
-        MySqlSelectQueryBlock query = explainToMySqlObject(sql);
-
-        query.accept(this.createMySqlMappingVisitor());
-
-        return SQLUtils.toMySqlString(query);
+    public SQLASTOutputVisitor createOutputVisitor(Appendable out) {
+        return provider.createOutputVisitor(this, out);
     }
 
-    public MySqlSelectQueryBlock explainToMySqlObject(String sql) {
-        MySqlSelectParser selectParser = new MySqlSelectParser(sql);
-        MySqlSelectQueryBlock query = (MySqlSelectQueryBlock) selectParser.query();
-        
-        if (this.maxLimit != null) {
-            if (query.getLimit() == null) {
-                Limit limit = new Limit();
-                limit.setRowCount(new SQLNumberExpr(maxLimit));
-                query.setLimit(limit);
-            } else {
-                SQLNumberExpr rowCountExpr = (SQLNumberExpr) query.getLimit().getRowCount();
-                int rowCount = rowCountExpr.getNumber().intValue();
-                if (rowCount > maxLimit.intValue()) {
-                    rowCountExpr.setNumber(maxLimit);
-                }
-            }
-        }
-        
-        return query;
+    public String explainToSQL(String sql) {
+        SQLSelectQueryBlock query = provider.explainToSQLObject(this, sql);
+
+        query.accept(this.createMappingVisitor());
+
+        StringBuilder out = new StringBuilder();
+        SQLASTOutputVisitor outputVisitor = createOutputVisitor(out);
+        query.accept(outputVisitor);
+
+        return out.toString();
     }
 }

src/main/java/com/alibaba/druid/mapping/MappingProvider.java

@@ -0,0 +1,13 @@
+package com.alibaba.druid.mapping;
+
+import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
+import com.alibaba.druid.sql.visitor.SQLASTOutputVisitor;
+
+public interface MappingProvider {
+
+    MappingVisitor createMappingVisitor(MappingEngine engine);
+
+    SQLASTOutputVisitor createOutputVisitor(MappingEngine engine, Appendable out);
+
+    SQLSelectQueryBlock explainToSQLObject(MappingEngine engine, String sql);
+}

src/main/java/com/alibaba/druid/mapping/MappingVisitor.java

@@ -3,13 +3,15 @@ package com.alibaba.druid.mapping;
 import java.util.Map;
 
 import com.alibaba.druid.sql.ast.statement.SQLTableSource;
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
-public interface MappingVisitor {
-	Entity getFirstEntity();
-	
-	Entity getEntity(String name);
-	
-	Map<String, Entity> getEntities();
-	
-	Map<String, SQLTableSource> getTableSources();
+public interface MappingVisitor extends SQLASTVisitor {
+
+    Entity getFirstEntity();
+
+    Entity getEntity(String name);
+
+    Map<String, Entity> getEntities();
+
+    Map<String, SQLTableSource> getTableSources();
 }

src/main/java/com/alibaba/druid/mapping/MySqlMappingProvider.java

@@ -0,0 +1,45 @@
+package com.alibaba.druid.mapping;
+
+import com.alibaba.druid.sql.ast.expr.SQLNumberExpr;
+import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
+import com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock;
+import com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock.Limit;
+import com.alibaba.druid.sql.dialect.mysql.parser.MySqlSelectParser;
+import com.alibaba.druid.sql.dialect.mysql.visitor.MySqlOutputVisitor;
+import com.alibaba.druid.sql.visitor.SQLASTOutputVisitor;
+
+public class MySqlMappingProvider implements MappingProvider {
+
+    @Override
+    public MappingVisitor createMappingVisitor(MappingEngine engine) {
+        return new MySqlMappingVisitor(engine.getEntities());
+    }
+
+    @Override
+    public SQLASTOutputVisitor createOutputVisitor(MappingEngine engine, Appendable out) {
+        return new MySqlOutputVisitor(out);
+    }
+
+    public SQLSelectQueryBlock explainToSQLObject(MappingEngine engine, String sql) {
+        MySqlSelectParser selectParser = new MySqlSelectParser(sql);
+        MySqlSelectQueryBlock query = (MySqlSelectQueryBlock) selectParser.query();
+
+        Integer maxLimit = engine.getMaxLimit();
+
+        if (maxLimit != null) {
+            if (query.getLimit() == null) {
+                Limit limit = new Limit();
+                limit.setRowCount(new SQLNumberExpr(maxLimit));
+                query.setLimit(limit);
+            } else {
+                SQLNumberExpr rowCountExpr = (SQLNumberExpr) query.getLimit().getRowCount();
+                int rowCount = rowCountExpr.getNumber().intValue();
+                if (rowCount > maxLimit.intValue()) {
+                    rowCountExpr.setNumber(maxLimit);
+                }
+            }
+        }
+
+        return query;
+    }
+}

src/main/java/com/alibaba/druid/mapping/OracleMappingProvider.java

@@ -0,0 +1,28 @@
+package com.alibaba.druid.mapping;
+
+import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
+import com.alibaba.druid.sql.dialect.oracle.ast.stmt.OracleSelectQueryBlock;
+import com.alibaba.druid.sql.dialect.oracle.parser.OracleSelectParser;
+import com.alibaba.druid.sql.dialect.oracle.visitor.OracleOutputVisitor;
+import com.alibaba.druid.sql.visitor.SQLASTOutputVisitor;
+
+public class OracleMappingProvider implements MappingProvider {
+
+    @Override
+    public MappingVisitor createMappingVisitor(MappingEngine engine) {
+        return new OracleMappingVisitor(engine.getEntities());
+    }
+
+    @Override
+    public SQLASTOutputVisitor createOutputVisitor(MappingEngine engine, Appendable out) {
+        return new OracleOutputVisitor(out);
+    }
+
+    public SQLSelectQueryBlock explainToSQLObject(MappingEngine engine, String sql) {
+        OracleSelectParser selectParser = new OracleSelectParser(sql);
+        OracleSelectQueryBlock query = (OracleSelectQueryBlock) selectParser.query();
+
+        return query;
+    }
+
+}