Spring Security Java Config Preview: Readability
In this post, I will discuss how to make your Spring Security Java configuration more readable. The post is intended to elaborate on a point from Spring Security Java Config Preview: Web Security where I stated:
By formatting our Java configuration code it is much easier to read. It can be read similar to the XML namespace equivalent where “and()” represents optionally closing an XML element.
Indentation
The indentation of Spring Security’s Java configuration really impacts its readability. In general, indentation like a bullet list should be preferred.
For a more concrete example, take a look at the following code:
http
// #1
.formLogin()
// #2
.loginPage("/login")
.failureUrl("/login?error")
// #3
.and()
// #4
.authorizeRequests()
// #5
.antMatchers("/signup","/about").permitAll()
.antMatchers("/admin/**").hasRole("ADMIN")
.anyRequest().authenticated();
- #1
formLogin
updates thehttp
object itself. The indentation offormLogin
is incremented from that ofhttp
(much like they way the<form-login>
is indented from<http>
) - #2
loginPage
andfailureUrl
update theformLogin
configuration. For example,loginPage
determines where Spring Security will redirect if log in is required. For this reason, each is a child offormLogin
. - #3
and
means we are done configuring the parent (in this caseformLogin
). This also implies that the next line will decrease indentation by one. When looking at the configuration you can read it ashttp
is configured withformLogin
andauthorizeRequests
. If we had nothing else to configure, theand
is not necessary. - #4 We decrease the indentation with
authorizeRequests
since it is not related to form based log in. Instead, its intent is to restrict access to various URLs. - #5 each
antMatchers
andanyRequest
modifies the authorization requirements forauthorizeRequests
. This is why each is a child ofauthorizeRequests
IDE Formatters
The indentation may cause problems with code formatters. Many IDE’s will allow you to disable formatting for select blocks of code with comments. For example, in STS/Eclipse you can use the comments of @formatter:off and @formatter:on to turn off and on code formatting. An example is shown below:
// @formatter:off
http
.formLogin()
.loginPage("/login")
.failureUrl("/login?error")
.and()
.authorizeRequests()
.antMatchers("/signup","/about").permitAll()
.antMatchers("/admin/**").hasRole("ADMIN")
.anyRequest().authenticated();
// @formatter:on
For this feature to work, make sure you have it enabled:
- Navigate to Preferences -> Java -> Code Style -> Formatter
- Click the Edit button
- Select the Off/On Tags tab
- Ensure Enable Off/On tags is selected
- You can optionally change the strings used for disabling and enabling formatting here too.
- Click OK
Comparison to XML Namespace
Our indentation also helps us relate the Java Configuration to the XML namespace configuration. This is not always true, but it does help. Let’s compare our configuration to the relevant XML configuration below.
http
.formLogin()
.loginPage("/login")
.failureUrl("/login?error")
.and()
.authorizeRequests()
.antMatchers("/signup","/about").permitAll()
.antMatchers("/admin/**").hasRole("ADMIN")
.anyRequest().authenticated();
The relevant, but not equivalent, XML configuration can be seen below. Note that the differences between how Spring Security will behave between these configurations is due to the different default values between Java Configuration and XML configuration.
<http use-expressions="true">
<form-login
login-page="/login"
authentication-failure-url="/login?error"
/> <!-- similar to and() -->
<intercept-url pattern="/signup" access="permitAll"/>
<intercept-url pattern="/about" access="permitAll"/>
<intercept-url pattern="/**" access="hasRole('ROLE_USER')"/>
</http>
- The first thing to notice is that the
http
and<http>
are quite similar. One difference is that Java Configuration usesauthorizeRequests
to specifyuse-expressions="true"
formLogin
and<form-login>
are quite similar. Each child offormLogin
is an XML attribute of<form-login>
. Based upon our explanation of indentation, the similarities are logical since XML attributes modify XML elements.- The
and()
underformLogin
is very similar to ending an XML element. - Each child of
authorizeRequests
is similar to each<intercept-urls>
, except that Java Configuration specifies requires-channel differently which helps reduce configuration in many circumstances.
Summary
You should now know how to consistently indent your Spring Security Java Configuration. By doing so your code will be more readable and be easier to translate to and from the XML configuration equivalents.