Article directory
-
- 1. Steps
- 2. Specific process
-
- 1. Introduce pom dependencies
- 2. Modify the configuration file
- 3. Unit testing
- 4. Test results
- 3. Redis running status
- 4. Practical application in the project
- 5. Locking solves the problem of cache breakdown
-
- Code one (there is a problem)
- Code two (problem solving)
- 6. New questions
- 7. Distributed lock
1. Step
Prerequisite: Redis has been installed
- 1. Introduce dependencies into pom
- 2. Configure in the configuration file
- 3. Used in the project
2. Specific process
1. Introduce pom dependencies
Versions are managed by the parent project
<!--Introduce redis-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
2. Modify the configuration file
spring:
redis:
host: 192.168.202.211
port: 6379
3. Unit testing
Please refer to the usage of stringRedisTemplate here
@Autowired
StringRedisTemplate stringRedisTemplate;
@Test
public void testRedis(){<!-- -->
ValueOperations<String, String> ops = stringRedisTemplate.opsForValue();
//save
ops.set("hello", UUID.randomUUID().toString());
//Inquire
String hello = ops. get("hello");
System.out.println("The data saved before is:" + hello);
}
4. Test results
3. Redis operation status
Here I use docker to install redis and check the running status of the container
4. Practical application in the project
code logic
test
access interface data
redis visualization tool view
5. Adding locks to solve the cache breakdown problem
Code one (there is a problem)
@Override
@Cacheable(value = {<!-- -->"category"}, key = "#root.methodName", sync = true)
public Map<String, List<Catalog2Vo>> getCatalogJsonDbWithSpringCache() {<!-- -->
//1. Put the json string in the cache, take out the json string, and need to reverse it to a usable object type [serialization and deserialization]
String catalogJSON = stringRedisTemplate.opsForValue().get("catalogJSON");
if(StringUtils.isEmpty(catalogJSON)){<!-- -->
//2, not in the cache, query the database
Map<String, List<Catalog2Vo>> calogJsonFromDb = getCategoriesDb();
//3. Put the found data into the cache, convert the object into json and put it in the cache
String s = JSON.toJSONString(calogJsonFromDb);
stringRedisTemplate.opsForValue().set("catalogJSON",s,1, TimeUnit.DAYS);
}
System.out.println("Cache data taken directly");
// convert to specified object
Map<String, List<Catalog2Vo>> result = JSON.parseObject(catalogJSON,new TypeReference<Map<String, List<Catalog2Vo>>>(){<!-- -->});
return result;
}
/ / Check out the three-level classification from the database
private Map<String, List<Catalog2Vo>> getCategoriesDb() {<!-- -->
synchronized (this){<!-- -->
// After getting the lock, you should go to the cache to confirm it again, if there is no need to continue querying in the cache
String catalogJSON = stringRedisTemplate.opsForValue().get("catalogJSON");
if(!StringUtils.isEmpty(catalogJSON)){<!-- -->
//There is data in the cache, return directly
Map<String, List<Catalog2Vo>> result = JSON.parseObject(catalogJSON,new TypeReference<Map<String, List<Catalog2Vo>>>(){<!-- -->});
return result;
}
System.out.println("There is no data in the cache, the database has been queried");
//Optimize business logic, only query the database once
List<CategoryEntity> categoryEntities = this. list();
// Find all first-level categories
List<CategoryEntity> level1Categories = getCategoryByParentCid(categoryEntities, 0L);
Map<String, List<Catalog2Vo>> listMap = level1Categories.stream().collect(Collectors.toMap(k->k.getCatId().toString(), v -> {<!-- -->
//Traverse to find out the secondary classification
List<CategoryEntity> level2Categories = getCategoryByParentCid(categoryEntities, v.getCatId());
List<Catalog2Vo> catalog2Vos=null;
if (level2Categories!=null){<!-- -->
//Encapsulate the second-level classification into vo and find out the third-level classification
catalog2Vos = level2Categories. stream(). map(cat -> {<!-- -->
// Traversing to find out the three-level classification and encapsulation
List<CategoryEntity> level3Catagories = getCategoryByParentCid(categoryEntities, cat.getCatId());
List<Catalog2Vo.Catalog3Vo> catalog3Vos = null;
if (level3Catagories != null) {<!-- -->
catalog3Vos = level3Catagories. stream()
.map(level3 -> new Catalog2Vo.Catalog3Vo(level3.getParentCid().toString(), level3.getCatId().toString(), level3.getName()))
.collect(Collectors.toList());
}
Catalog2Vo catalog2Vo = new Catalog2Vo(v.getCatId().toString(), cat.getCatId().toString(), cat.getName(), catalog3Vos);
return catalog2Vo;
}).collect(Collectors.toList());
}
return catalog2Vos;
}));
return listMap;
}
}
Use jmeter to measure its pressure
Looking at the console, the ideal situation is that the database is only queried once. In fact, it has been queried many times. The reason for this problem is that a user releases the lock after querying the data. When the data has not been written into the cache, the second user gets the lock again. At this time, the data has not been cached in the cache, causing the database to be queried again. Need to optimize code logic
Code 2 (problem solving)
Optimize the code logic, and the pressure test process is the same as above.
6. New question
Local locks cannot be locked in distributed situations
7. Distributed lock
to be edited