// annotations/database/TableCreator.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Reflection-based annotation processor
// {java annotations.database.TableCreator
// annotations.database.Member}
package annotations.database;
import java.lang.annotation.*;
import java.lang.reflect.*;
import java.util.*;

public class TableCreator {
 public static void
 main(String[] args) throws Exception {
 if(args.length < 1) {
 System.out.println(
 "arguments: annotated classes");
 System.exit(0);
 }
 for(String className : args) {
 Class<?> cl = Class.forName(className);
 DBTable dbTable = cl.getAnnotation(DBTable.class);
 if(dbTable == null) {
 System.out.println(
 "No DBTable annotations in class " +
 className);
 continue;
 }
 String tableName = dbTable.name();
 // If the name is empty, use the Class name:
 if(tableName.length() < 1)
 tableName = cl.getName().toUpperCase();
 List<String> columnDefs = new ArrayList<>();
 for(Field field : cl.getDeclaredFields()) {
 String columnName = null;
 Annotation[] anns =
 field.getDeclaredAnnotations();
 if(anns.length < 1)
 continue; // Not a db table column
 if(anns[0] instanceof SQLInteger) {
 SQLInteger sInt = (SQLInteger) anns[0];
 // Use field name if name not specified
 if(sInt.name().length() < 1)
 columnName = field.getName().toUpperCase();
 else
 columnName = sInt.name();
 columnDefs.add(columnName + " INT" +
 getConstraints(sInt.constraints()));
 }
 if(anns[0] instanceof SQLString) {
 SQLString sString = (SQLString) anns[0];
 // Use field name if name not specified.
 if(sString.name().length() < 1)
 columnName = field.getName().toUpperCase();
 else
 columnName = sString.name();
 columnDefs.add(columnName + " VARCHAR(" +
 sString.value() + ")" +
 getConstraints(sString.constraints()));
 }
 StringBuilder createCommand = new StringBuilder(
 "CREATE TABLE " + tableName + "(");
 for(String columnDef : columnDefs)
 createCommand.append(
 "\n " + columnDef + ",");
 // Remove trailing comma
 String tableCreate = createCommand.substring(
 0, createCommand.length() - 1) + ");";
 System.out.println("Table Creation SQL for " +
 className + " is:\n" + tableCreate);
 }
 }
 }
 private static
 String getConstraints(Constraints con) {
 String constraints = "";
 if(!con.allowNull())
 constraints += " NOT NULL";
 if(con.primaryKey())
 constraints += " PRIMARY KEY";
 if(con.unique())
 constraints += " UNIQUE";
 return constraints;
 }
}
/* Output:
Table Creation SQL for annotations.database.Member is:
CREATE TABLE MEMBER(
 FIRSTNAME VARCHAR(30));
Table Creation SQL for annotations.database.Member is:
CREATE TABLE MEMBER(
 FIRSTNAME VARCHAR(30),
 LASTNAME VARCHAR(50));
Table Creation SQL for annotations.database.Member is:
CREATE TABLE MEMBER(
 FIRSTNAME VARCHAR(30),
 LASTNAME VARCHAR(50),
 AGE INT);
Table Creation SQL for annotations.database.Member is:
CREATE TABLE MEMBER(
 FIRSTNAME VARCHAR(30),
 LASTNAME VARCHAR(50),
 AGE INT,
 REFERENCE VARCHAR(30) PRIMARY KEY);
*/