{"id":6373,"date":"2024-08-21T12:52:46","date_gmt":"2024-08-21T12:52:46","guid":{"rendered":"https:\/\/www.solutionstreet.com\/blog\/?p=6373"},"modified":"2024-08-21T12:57:28","modified_gmt":"2024-08-21T12:57:28","slug":"spring-declarative-caching","status":"publish","type":"post","link":"https:\/\/www.solutionstreet.com\/blog\/2024\/08\/21\/spring-declarative-caching\/","title":{"rendered":"Spring Declarative Caching"},"content":{"rendered":"
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\"\"<\/figure>\n<\/div>\n\n\n

Introduction<\/h2>\n\n\n\n

I had occasion at work recently to consider using Spring\u2019s @Cacheable<\/code> annotation. I searched the web for some hints on how to use it, but wasn\u2019t satisfied with any of the results. Even my favorite source1<\/a><\/sup> of bite-size Java code samples had examples that I felt were too<\/a> simple<\/a>. Using \u201clookup\u201d methods as examples of places where you may want to put @CacheEvict<\/code> and @CachePut<\/code> annotations seemed misleading to me.<\/p>\n\n\n\n

So, at the very least, I wanted to provide more substantial examples. In particular, I wanted to show why Spring\u2019s default cache implementation requires careful thought in a distributed application environment.<\/p>\n\n\n\n

In the process, I ended up going off the rails a bit. I spent way more time setting up an environment in which I could run my examples than I did writing actual Java code. But, in a way, that\u2019s great! If you came here to read Java code, the good new is: there\u2019s not a lot of it.<\/p>\n\n\n\n

Code<\/h2>\n\n\n\n

For this blog post, I bootstrapped a Spring project using the spring initializr<\/a> and then put it on GitHub<\/a>.<\/p>\n\n\n\n

To run the examples with the least amount of fuss, you\u2019ll need Docker<\/code>, Docker Compose<\/code>, and (gnu) make<\/code>, curl<\/code>, and jq<\/code>. If you have those tools, things should<\/em> go smoothly. However, it is<\/em> software\u2026 so, you know\u2026 good luck. If it breaks, you\u2019ve got the source code!<\/p>\n\n\n\n

For examples that show a command typed at a prompt, this character is my prompt: \u2717<\/code><\/p>\n\n\n\n

Big Picture<\/h2>\n\n\n\n

Broadly speaking, you\u2019d like to cache return values of methods that are expensive to compute. You can measure \u201cexpensive\u201d in different ways (e.g., CPU or memory used); but often, when we say \u201cexpensive,\u201d we mean \u201cit takes too much time.\u201d<\/p>\n\n\n\n

If we assume that all methods in question are \u201cfunctions\u201d in the mathematical sense \u2013 i.e., given the same inputs (to include the instance the method is operating on), they always give the same output \u2013 then caching is pretty simple. Any return value of such a method can be cached indefinitely, and the only decisions you need to make with respect to your cache are:<\/p>\n\n\n\n

    \n
  1. How big can it get?<\/li>\n\n\n\n
  2. Which eviction policy do you choose to ensure the size constraint is maintained?<\/li>\n<\/ol>\n\n\n\n

    If we do not<\/em><\/strong> assume that the method in question are functions, then we can consider much more interesting examples.<\/p>\n\n\n\n

    For instance, consider a service that, given an identifier, retrieves a record from a relational database. Assume that this database has multiple clients, each of which can update records. Should you expect that, given the same identifier, the service should return the same record now that it did six hours ago? Of course not; the record could have been updated in the intervening time.<\/p>\n\n\n\n

    Sample Application<\/h2>\n\n\n\n

    The sample application includes a very simple service for managing a database of books. It uses Spring declarative caching to minimize database lookups. It lets you:<\/p>\n\n\n\n

      \n
    1. Retrieve books<\/li>\n\n\n\n
    2. Change books\u2019 titles<\/li>\n<\/ol>\n\n\n\n

      Following is a stripped down version of the RestController class that implements the API endpoints for our service (see the source code for the complete class).<\/p>\n\n\n\n

      <\/code><\/pre>\n\n\n\n
      @RequestMapping(\"\/books\")\npublic<\/strong> class<\/strong> BookRestController {\n  private<\/strong> final<\/strong> BookRepository bookRepository;\n\n  @GetMapping(\"\/clear\")\n  @CacheEvict(cacheNames = \"books\", allEntries = true<\/strong>)\n  public<\/strong> void<\/strong> clearCache() {\n  }\n\n  @GetMapping\n  public<\/strong> Collection<Book> books() {\n    return<\/strong> bookRepository.findAll();\n  }\n\n  @GetMapping(\"\/{isbn}\")\n  @Cacheable(cacheNames = \"books\")\n  public<\/strong> Book bookByIsbn(@PathVariable(\"isbn\") String isbn) {\n    return<\/strong> bookRepository.findByIsbn(isbn);\n  }\n\n  @GetMapping(\"\/{isbn}\/badUpdateTitle\/{title}\")\n  public<\/strong> Book badUpdateTitle(@PathVariable(\"isbn\") String isbn,\n                             @PathVariable(\"title\") String title) {\n    return<\/strong> bookRepository.save(bookRepository.findByIsbn(isbn).withTitle(title));\n  }\n\n  @GetMapping(\"\/{isbn}\/betterUpdateTitle\/{title}\")\n  @CacheEvict(cacheNames = \"books\", key = \"#isbn\")\n  public<\/strong> Book betterUpdateTitle(@PathVariable(\"isbn\") String isbn,\n                                @PathVariable(\"title\") String title) {\n    return<\/strong> bookRepository.save(bookRepository.findByIsbn(isbn).withTitle(title));\n  }\n\n  @GetMapping(\"\/{isbn}\/bestUpdateTitle\/{title}\")\n  @CachePut(cacheNames = \"books\", key = \"#isbn\")\n  public<\/strong> Book bestUpdateTitle(@PathVariable(\"isbn\") String isbn,\n                              @PathVariable(\"title\") String title) {\n    return<\/strong> bookRepository.save(bookRepository.findByIsbn(isbn).withTitle(title));\n  }\n}<\/code><\/pre>\n\n\n\n
      Some notes on the methods and their use of Spring\u2019s declarative caching.<\/p>\n\n\n\n