Doing more with DAO in Java

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Doing more with DAO
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contact.setFirstName( getAttributeValue(attributes, "givenName")); contact.setMail(getAttributeValue(attributes, "mail")); contact.setUserId( getAttributeValue(attributes, "uid")); return contact; } private String getAttributeValue( Attributes attributes, String attrID ) { Attribute attribute = attributes.get(attrID); try { return (null==attribute "":(String)attribute.get()); } catch (NamingException e) { throw new DaoException(e); } }
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The Attributes interface is part of the JNDI package that comes with Sun s JDK, and is implemented by the BasicAttributes class, which is also part of that package. The Contact class is our bean that we want to map to our LDAP directory. Finally, the getAttributeValue() method is a helper method that simplifies the mapping process by handling null values and turning JNDI-specific exceptions into DaoExceptions. Just as with other DAO implementations, we need to make some decisions about where and how we will get to our database. If you are working with a J2EE container that can provide you with a JNDI context, you might be tempted to use it. If it meets your needs, there is no reason not to. However, there are some tradeoffs when doing this. Although this approach will simplify the code, it will make testing more difficult. Depending on your requirements, this may be an acceptable sacrifice. In this example, we wanted to make things as testable as possible, so we used constructor-based injection to configure the DAO class at runtime. Because the iBATIS DAO does not allow this, we also created a default constructor that uses the two values we wanted as the defaults. In section 11.3, we look at using the Spring framework for our DAO layer, which allows us to do this via configuration files, but for now, let s use the default constructor method. The second constructor takes two parameters for the two settings I hardcoded into the default constructor. One of those was the determination of the LDAP DN attribute for our contact bean. This attribute is analogous to the primary key of a
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Using the DAO pattern with other data sources
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database table, but is unique through the entire directory, not just in a single segment of it like the primary key for a row in a table. The following method in the DAO implementation creates a unique DN for our contact bean:
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private String getDn(String userId){ return MessageFormat.format(this.dnTemplate, userId); }
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The second setting we need is for getting the initial directory context. The default constructor for our DAO will use the hardcoded properties to connect to our LDAP directory, but again, the second constructor will allow us to inject custom properties if needed for other purposes. Those properties are used to get the initial directory context:
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private DirContext getInitialContext() { DirContext ctx = null; try { ctx = new InitialDirContext(env); } catch (NamingException e) { log.error("Exception getting initial context", e); throw new DaoException(e); } return ctx; }
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Now that we have all of the required infrastructure code in place to deal with mapping our bean and connecting to our LDAP directory, we can start to build our DAO implementation. The first method we will look at is the simplest we will look up a contact by userId. Here is the code to implement that method:
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public Contact getById(String id) { DirContext ctx = getInitialContext(); Attributes attributes; try { attributes = ctx.getAttributes(getDn(id)); } catch (NamingException e) { throw new DaoException(e); } return getContact(attributes); }
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Here, we take the directory context, and use it to get the attributes of our contact, based on the DN of the passed-in user s id value. Once we have the attributes, we convert them into a contact bean and return it. If an LDAP-specific NamingException is thrown, it is re-thrown as DaoException instead to make sure that the method signature does not indicate the data source.
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