decrease memory used

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterString.java

@@ -0,0 +1,34 @@
+package com.alibaba.druid.proxy.jdbc;
+
+import java.sql.Types;
+import java.util.Calendar;
+
+public class JdbcParameterString implements JdbcParameter {
+
+    private final String value;
+
+    public JdbcParameterString(String value){
+        this.value = value;
+    }
+
+    @Override
+    public Object getValue() {
+        return value;
+    }
+
+    @Override
+    public long getLength() {
+        return 0;
+    }
+
+    @Override
+    public Calendar getCalendar() {
+        return null;
+    }
+
+    @Override
+    public int getSqlType() {
+        return Types.VARCHAR;
+    }
+
+}