@Caching With Multiple Keys

Question

I have a service that takes in a DTO and returns some result:

@Override
public int foo(Bar bar) {
    ....
}

Bar is as follows (simplified):

public class Bar {
    public int id;
    public String name;
    public String baz;

    @Override
    public int hashCode() {
        //this is already being defined for something else
        ...
    }

    @Override
    public boolean equals(Object o) {
        //this is already being defined for something else
        ...
    }
}

I want to use @Cacheable on the foo method; however, I want to hash on the id and name properties, but not baz. Is there a way to do this?

Does this answer your question? [@Cacheable key on multiple method arguments](https://stackoverflow.com/questions/14072380/cacheable-key-on-multiple-method-arguments) — Balázs Németh, Jan 21 '21 at 11:08

score 53 · Answer 1 · edited May 23 '17 at 12:34

53

You can use this approach also

@Override
@Cacheable(key="{#bar.name, #bar.id}")
public int foo(Bar bar) {
    ....
}

It is suggested not to use hashcode as keys @Cacheable key on multiple method arguments

edited May 23 '17 at 12:34

Community

1
1

answered Jun 12 '14 at 20:19

vsingh

6,365
3
53
57

2

But when I use this approach it's throwing `java.lang.ClassCastException: Invalid key type, expected : org.springframework.cache.interceptor.SimpleKey but was : java.util.ArrayList`. How can I get over this? – Sanjay May 06 '21 at 08:09

score 20 · Accepted Answer · answered Nov 14 '12 at 15:51

20

Yes, you can specify using a Spring-EL expression along these lines:

@Override
@Cacheable(key="#bar.name.concat('-').concat(#bar.id)")
public int foo(Bar bar) {
    ....
}

or define a modified hashCode on bar and call that:

@Override
@Cacheable(key="#bar.hashCodeWithIdName")
public int foo(Bar bar) {
    ....
}

answered Nov 14 '12 at 15:51

Biju Kunjummen

49,138
14
112
125

If '-' is public static final String data. How should I do? – study_20160808 May 12 '21 at 07:48
Be careful on the NullPointerException in case name or id are null – Antonio May 16 '23 at 09:12

score 2 · Answer 3 · answered Aug 23 '17 at 14:33

Both answers by @Biju and @vsingh are correct; but I would like to add one more alternative if the Bar object you are trying to cache is complex or the foo method contains a large amount of parameters using SpEL might not be the most ideal solution for generating the key.

Alternatively you may want to consider keyGenerator.

Example:

@Override
@Cacheable(value="barCahceKey", keyGenerator="barKeyGenerator")
public int foo(Bar bar) {
  ....
}

@Component
public class BarKeyGenerator implements KeyGenerator {
@Override
public Object generate(Object o, Method method, Object... objects) {
      // TODO logic to generate unique key
      return "Bar_Key_Generator_With_Params_etc";
    }
}

With this approach you have the fully flexibility of how the key is constructed.

KeyGenerator API

Custom keyGenerator allow to create only 1 key. What about having multipe keys from KeyGenerator? This KeyGenerator only return Object not array of object. So, I guess custom KeyGenerator cannot be used for multiple key generation. — Akanksha gore, Jan 28 '22 at 06:22

score 2 · Answer 4 · answered Nov 20 '19 at 10:19

2

You can use Spring SimpleKey class

@Cacheable(value = "barCache", key = "new org.springframework.cache.interceptor.SimpleKey(#bar.id, #bar.name)")

answered Nov 20 '19 at 10:19

Abdelrahman Elattar

460
5
5

This works for but why does [@vsingh](https://stackoverflow.com/a/24193252/9079093) solution gives me `java.lang.ClassCastException: Invalid key type, expected : org.springframework.cache.interceptor.SimpleKey but was : java.util.ArrayList` exception? – Sanjay May 06 '21 at 14:35
But why does it require `key = "new org.springframework.cache.interceptor.SimpleKey(#bar.id, #bar.name)"` instead of `key = "{#bar.id, #bar.name}"` – Sanjay May 06 '21 at 14:59

Adam111p · Answer 5 · 2022-06-09T09:59:59.250

  @Cacheable(value = "myCacheByNameUserCity", key = "T(java.util.Objects).hash(#name, #user, #city)")
  public User getUser(String name, String user,String city)

I propose this method with Object.hash, because "new org.springframework.cache.interceptor.SimpleKey (# bar.id, # bar.name)" returns toString () So it returns:

getClass().getSimpleName() + " [" + StringUtils.arrayToCommaDelimitedString(this.params) + "]";

So finally it returns "SimpleKey [bla,blaa, blalala]" not a unique code

score 0 · Answer 6 · answered May 14 '23 at 10:04

Example for a KeyGenerator-implementation with multiple keys

public class MyKeyGenerator implements KeyGenerator {

  public Object generate(Object target, Method method, Object... params) {
    if (params.length > 2) {
        // only the first two, please! this was useful in my case.
        // omit or use like this, if (not) needed
        params = Arrays.copyOf(params, 2);
    }
    var key = String.format("mykey_%s", StringUtils.arrayToDelimitedString(params, "_")); 
    return key;
  }
}

In your CacheConfig you inject the bean like:

@Bean("myKeyGenerator") KeyGenerator myKeyGenerator() {
    return new MyCacheKeyGenerator();
}

And in your repository-class like:

// assuming you also defined a "myCache" in your cache-config!

@Cacheable(value = "myCache", keyGenerator = "myKeyGenerator", unless="#result == null")
public byte[] getMyData(int objectId, int objectType, boolean furtherParams, int willBeIgnored) {
}

@CacheEvict(value = "myCache", keyGenerator = "myKeyGenerator")
public void storeMyData(int id, int type, byte[] myData, int changingUserId) {
   // store here and do the same annotation for the delete-method
}

score -1 · Answer 7 · answered Feb 28 '19 at 05:32

-1

The keys from the same Object, you can use object.hashCode(), so you don't need to specific keys one by one

@Override
@Cacheable(key="#bar.hashCode()")
public int foo(Bar bar) {
    ....
}

OR if you have an object and another key

@Override
@Cacheable(key="{#bar.hashCode(), #anotherKey}")
public int foo(Bar bar) {
    ....
}

I think this is a better solution.

answered Feb 28 '19 at 05:32

Rady Archuleta

29
4

Hash codes are dangerous as they aren't guaranteed to be unique. – NBJack Apr 16 '21 at 20:19

@Caching With Multiple Keys

7 Answers7

Example for a KeyGenerator-implementation with multiple keys