Cleanest way to build an SQL string in Java

Question

I want to build an SQL string to do database manipulation (updates, deletes, inserts, selects, that sort of thing) - instead of the awful string concat method using millions of "+"'s and quotes which is unreadable at best - there must be a better way.

I did think of using MessageFormat - but its supposed to be used for user messages, although I think it would do a reasonable job - but I guess there should be something more aligned to SQL type operations in the java sql libraries.

Would Groovy be any good?

Any help much appreciated.

Answer 1

I tend to use Spring's Named JDBC Parameters so I can write a standard string like "select * from blah where colX=':someValue'"; I think that's pretty readable.

An alternative would be to supply the string in a separate .sql file and read the contents in using a utility method.

Oh, also worth having a look at Squill: https://squill.dev.java.net/docs/tutorial.html

Answer 2

If you put the SQL strings in a properties file and then read that in you can keep the SQL strings in a plain text file.

That doesn't solve the SQL type issues, but at least it makes copying&pasting from TOAD or sqlplus much easier.

Answer 3

Why do you want to generate all the sql by hand? Have you looked at an ORM like Hibernate Depending on your project it will probably do at least 95% of what you need, do it in a cleaner way then raw SQL, and if you need to get the last bit of performance you can create the SQL queries that need to be hand tuned.

Answer 4

First of all consider using query parameters in prepared statements:

PreparedStatement stm = c.prepareStatement("UPDATE user_table SET name=? WHERE id=?");
stm.setString(1, "the name");
stm.setInt(2, 345);
stm.executeUpdate();

The other thing that can be done is to keep all queries in properties file. For example in a queries.properties file can place the above query:

update_query=UPDATE user_table SET name=? WHERE id=?

Then with the help of a simple utility class:

public class Queries {

    private static final String propFileName = "queries.properties";
    private static Properties props;

    public static Properties getQueries() throws SQLException {
     InputStream is = 
      Queries.class.getResourceAsStream("/" + propFileName);
     if (is == null){
      throw new SQLException("Unable to load property file: " + propFileName);
     }
     //singleton
     if(props == null){
      props = new Properties();
      try {
       props.load(is);
      } catch (IOException e) {
       throw new SQLException("Unable to load property file: " + propFileName + "\n" + e.getMessage());
      }   
     }
     return props;
    }

    public static String getQuery(String query) throws SQLException{
     return getQueries().getProperty(query);
    }

}

you might use your queries as follows:

PreparedStatement stm = c.prepareStatement(Queries.getQuery("update_query"));

This is a rather simple solution, but works well.

Answer 5

I am wondering if you are after something like Squiggle. Also something very useful is jDBI. It won't help you with the queries though.

Answer 6

I would have a look at Spring JDBC. I use it whenever I need to execute SQLs programatically. Example:

int countOfActorsNamedJoe
    = jdbcTemplate.queryForInt("select count(0) from t_actors where first_name = ?", new Object[]{"Joe"});

It's really great for any kind of sql execution, especially querying; it will help you map resultsets to objects, without adding the complexity of a complete ORM.

Answer 7

One technology you should consider is SQLJ - a way to embed SQL statements directly in Java. As a simple example, you might have the following in a file called TestQueries.sqlj:

public class TestQueries
{
    public String getUsername(int id)
    {
        String username;
        #sql
        {
            select username into :username
            from users
            where pkey = :id
        };
        return username;
    }
}

There is an additional precompile step which takes your .sqlj files and translates them into pure Java - in short, it looks for the special blocks delimited with

#sql
{
    ...
}

and turns them into JDBC calls. There are several key benefits to using SQLJ:

• completely abstracts away the JDBC layer - programmers only need to think about Java and SQL
• the translator can be made to check your queries for syntax etc. against the database at compile time
• ability to directly bind Java variables in queries using the ":" prefix

There are implementations of the translator around for most of the major database vendors, so you should be able to find everything you need easily.

Answer 8

How do you get string concatenation, aside from long SQL strings in PreparedStatements (that you could easily provide in a text file and load as a resource anyway) that you break over several lines?

You aren't creating SQL strings directly are you? That's the biggest no-no in programming. Please use PreparedStatements, and supply the data as parameters. It reduces the chance of SQL Injection vastly.

Answer 9

I second the recommendations for using an ORM like Hibernate. However, there are certainly situations where that doesn't work, so I'll take this opportunity to tout some stuff that i've helped to write: SqlBuilder is a java library for dynamically building sql statements using the "builder" style. it's fairly powerful and fairly flexible.

Answer 10

I have been working on a Java servlet application that needs to construct very dynamic SQL statements for adhoc reporting purposes. The basic function of the app is to feed a bunch of named HTTP request parameters into a pre-coded query, and generate a nicely formatted table of output. I used Spring MVC and the dependency injection framework to store all of my SQL queries in XML files and load them into the reporting application, along with the table formatting information. Eventually, the reporting requirements became more complicated than the capabilities of the existing parameter mapping frameworks and I had to write my own. It was an interesting exercise in development and produced a framework for parameter mapping much more robust than anything else I could find.

The new parameter mappings looked as such:

select app.name as "App", 
       ${optional(" app.owner as "Owner", "):showOwner}
       sv.name as "Server", sum(act.trans_ct) as "Trans"
  from activity_records act, servers sv, applications app
 where act.server_id = sv.id
   and act.app_id = app.id
   and sv.id = ${integer(0,50):serverId}
   and app.id in ${integerList(50):appId}
 group by app.name, ${optional(" app.owner, "):showOwner} sv.name
 order by app.name, sv.name

The beauty of the resulting framework was that it could process HTTP request parameters directly into the query with proper type checking and limit checking. No extra mappings required for input validation. In the example query above, the parameter named serverId would be checked to make sure it could cast to an integer and was in the range of 0-50. The parameter appId would be processed as an array of integers, with a length limit of 50. If the field showOwner is present and set to "true", the bits of SQL in the quotes will be added to the generated query for the optional field mappings. field Several more parameter type mappings are available including optional segments of SQL with further parameter mappings. It allows for as complex of a query mapping as the developer can come up with. It even has controls in the report configuration to determine whether a given query will have the final mappings via a PreparedStatement or simply ran as a pre-built query.

For the sample Http request values:

showOwner: true
serverId: 20
appId: 1,2,3,5,7,11,13

It would produce the following SQL:

select app.name as "App", 
       app.owner as "Owner", 
       sv.name as "Server", sum(act.trans_ct) as "Trans"
  from activity_records act, servers sv, applications app
 where act.server_id = sv.id
   and act.app_id = app.id
   and sv.id = 20
   and app.id in (1,2,3,5,7,11,13)
 group by app.name,  app.owner,  sv.name
 order by app.name, sv.name

I really think that Spring or Hibernate or one of those frameworks should offer a more robust mapping mechanism that verifies types, allows for complex data types like arrays and other such features. I wrote my engine for only my purposes, it isn't quite read for general release. It only works with Oracle queries at the moment and all of the code belongs to a big corporation. Someday I may take my ideas and build a new open source framework, but I'm hoping one of the existing big players will take up the challenge.