Java - Storing SQL statements in an external file [closed]

Answer 1

dynamic-query is a good open source framework for those want something between JDBC and ORM.

1 plain SQL. - It saves plain sql to external files. no redundant tags, supports comments.

/* It also supports comment.
This code is in an external file 'sample.sql', Not inisde java code.*/
listUsers : select * from user_table
where user_id= $$;  /* $$ will automatically catch a parameter userId */

2 expandable SQL. -It supports parameters, including other files and sub query.

listUsers:
select
    id, amount, created
    @checkEmail{ ,email } 
from user_table
where amount > $amt and balance < $amt
    @checkDate { and created = $$ }
    @checkEmail{ and email in (
        select email from vip_list ) } ;        
/* Above query can be four queries like below.
1. listUsers
2. listUsers.checkDate 
3. listUsers.checkEmail
4. listUsers.checkDate.checkEmail 
*/



-- It can include other files like below
& ../hr/additional hr.sql ; 
& ../fi/additional fi.sql ;

Java example code using above. setting values to db.

QueryUtil qu = qm.createQueryUtil("selectAll");
try {
    qu.setConnection(conn);

    // with native jdbc
    qu.setString("alpha");
    qu.setDouble(10.1);
    qu.executeQuery();

    // or with bean
    qu.executeQuery(new User("alpha", 10.1));

    // or with map
    Map<String, Object> map=new HashMap<String, Object>();
    map.put("userName", "alpha");
    map.put("amt", 10.1);
    qu.executeQuery(map);

    // or with array
    qu.executeQueryParameters("alpha", 10.1);

Java example code using above. getting values from db.

    while (qu.next()) // == qu.rs.next()
    {
        // native jdbc
        String usreName = qu.getString("user_name"); 
        double amt = qu.getDouble("amt");

        // or bean
        User user = new User();
        qu.updateBean(user);

        // or array
        Object[] values = qu.populateArray();
    }
} catch (Exception e) {
    e.printStackTrace();
} finally {
    qu.closeJust();
}

Answer 2

It's simple and reliable to do using classes from Spring. Take your SQL files and save them in some location on your classpath. This can be in a JAR file that only contains SQL if you want. Then use Spring's ClassPathResource to load the file into a stream and use Apache IOUtils to convert it into a String. You can then execute the SQL using SimpleJdbcTemplate, or DB code of your choice.

I suggest you create a utility class that takes a simple Java class with public String fields that correspond to the SQL file names following a convention of your choosing. Then use reflection in conjunction with the ClassPathResource class to go find the SQL files conforming to your naming convention and assign them to the String fields. After that just refer to the class fields when you need the SQL. It's simple, works great, and achieves the goal you want. It also uses well worn classes and techniques. Nothing fancy. I did it couple years back. Works great. Too lazy to go get the code. You'll have no time figuring it out yourself.

Answer 3

You can use Spring and have your sql statements stored in your beans file that are injected when you get the class from your bean factory. That class can also to use an instance of SimpleJDBCTemplate that can be configured via the bean file to help simplify your code.

Answer 4

A simple solution we have implemented when faced with this was to externalize the SQL/DML into a file (mySql.properties), then use MessageFormat.format(String[] args) to inject dynamic properties into the SQL.

For example: mySql.properties:

select    *
    from      scott.emp
              join scott.dept on (emp.deptno = dept.deptno)
    where     emp.ename = {0}

Utility methods:

public static String format(String template, Object[] args) {
    String cleanedTemplate = replaceSingleQuotes(template);
    MessageFormat mf = new MessageFormat(cleanedTemplate);
    String output = mf.format(args);
    return output;
}
private static String replaceSingleQuotes(String template) {
    String cleaned = template.replace("'", "''");
    return cleaned;
}

Then use it like so:

String sqlString = youStringReaderImpl("/path/to/file");
String parsedSql = format(sqlString, new String[] {"bob"});

Answer 5

You can also use the QueryLoader class in Apache Commons DbUtils, which will read the sql from a properties file. However, you will have to use DbUtils which sort of serves the same purpose as the JDBCTemplate.

Answer 6

You can use velocity to have "scriptable" sql templates that you can use to work with the files in a flexible way. You have primitive statements like conditionals and loops to build your sql commands.

But I strongly suggest to use prepared statements and/or stored procedures. Building your SQL the way you're planning will make you vulnerable to SQL injection, the DB server will not be able to cache the sql queries (which will lead to bad performance).

BTW: You can store the definition of the prepared statements in files too. This is not the best solution but pretty close to it and you get the benefit of SQL-injection protection and performance.

When your SQL schema is not build to work with prepared statements or stored procedures you might want to rethink your schema. Maybe it needs to be refactored.