OnJava8-Examples/annotations/database/TableCreator.java

// annotations/database/TableCreator.java
// (c)2020 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);
*/