Question

I have a web application that executes on tomcat 6.

I have a MysqlDb class that uses a BasicDataSource from a spring JDBC.

so far I’ve used the following bean configuration in web.xml:

<bean id="MysqlDb" class="com.xpogames.gamesisland.mysql.MysqlDb">
    <property name="idDataSource" ref="idDataSource"/>
 </bean>

and I had the following setter function:

  public void setidDataSource(BasicDataSource ds) {
    this._dataSource=(DataSource)ds;
    this._simpleJdbcTemplate = new SimpleJdbcTemplate(_dataSource);
    this._jdbcTemplate = new JdbcTemplate(_dataSource);
 }

I want to convert my class to use static functions, so I created an empty private constructor so the class won’t explicitly instantiated by callers.

besides that I changed the setidDataSource function to a static function, but when I try to do that I get the following error:

Error setting property values; nested exception is org.springframework.beans.NotWritablePropertyException: Invalid property ‘idDataSource’ of bean class [com.xpogames.gamesisland.mysql.MysqlDb]: Bean property ‘idDataSource’ is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?

is there a way to resolve this issue in web.xml or do I need to manually
fetch the ServletContext

ServletContext servletContext = this.getServletContext();
this._context = WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);

and fetch the bean from there and just remove the lines i printed here from web.xml ?

Answer 1

I understand know that I had a bad implementation idea. I still need a constructor, so building a class with static functions and static init is a bad idea, and trying to execute a static setter from a bean is not logical and impossible.

Instead I changed the class to be a singleton class, so I will be able to use it anywhere in my application and it will be constructed only once.

thanks for all the information.

update

I still don’t know if that’s a good method, but at least it works.

in my red-web.xml (consider it as spring applicationContext.xml), I have the following:

 <bean id="MysqlDb" class="com.xpogames.gamesisland.mysql.MysqlDb" init-method="getInstance">
    <property name="idDataSource" ref="idDataSource"/>
 </bean>

Here it creates a MysqlDb bean and configure it to use the getInstance() init method if MysqlDb Class. i made sure to have a setidDataSource() function in mysqlDb class for the datasource to be properly set.

<bean id="web.handler" class="com.xpogames.gamesisland.Application">
    <property name="MysqlDb" ref="MysqlDb"/>
</bean>

Here, I create the main bean of my application and I made sure to have the function setMysqlDb for the MysqlDb class to be set from the bean configuration.

So far mysqlDb acts as a singelton class because it’s constructor is protected and it creates the instance only once:

public static MysqlDb getInstance() {
    if (instance == null) {
        instance = new MysqlDb();
    }
    return instance;
}

The problem that I encountered was that in other parts of my application whenever I used getInstance(), the MysqlDb class would come up and all the variables that where set with setidDataSource where null.

so resolve that issue I created another function called setInstance in mysqlDb:

public static void setInstance(MysqlDb db) {
instance=db;
}

this is my main setMysqlDb function in my main application:

public void setMysqlDb(MysqlDb db) {
    this._mysqlDb=db;
    /* it seems that without forcing a setInstance on the class, whenever other classes
     * would try to getInstance(), variables that are supposed to be configured by the bean
     * would be empty. this resolves that issue
     */
    MysqlDb.setInstance(db);
}

so this configuration works. it’s obviously not the recommended or best solution! but it seems that I need to read and learn further before I come up with a better solution.