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Java Problems Summary

Solving Maven Remote Repository Jar Download Failures​

Go to Maven Repository to find the corresponding dependency and download it.

Go to the download directory and execute the following command, replacing -DgroupId, -DartifactId, -Dversion, -Dfile

mvn install:install-file -DgroupId=io.confluent -DartifactId=kafka-schema-registry-client -Dversion=4.1.0 -Dpackaging=jar  -Dfile=kafka-schema-registry-client-4.1.0.jar

mvnw clean occurs Some Enforcer rules have failed​

Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:1.4.1:enforce
(enforce-versions) on project SIMI: Some Enforcer rules have failed. Look above for
specific messages explaining why the rule failed. -> [Help 1]

not solved! stackoverflow website

To skip enforcer (not always working)

mvn clean install -Denforcer.skip=true

To continue the build if error

mvn clean install -Denforcer.fail=false
./mvnw clean install -DskipDistribution=true  -Denforcer.skip=true

UncategorizedSQLException when SQL query null value is mapped to int type​

Change BO property from int to Integer type

org.springframework.jdbc.UncategorizedSQLException: SqlMapClient operation; 
uncategorized SQLException for SQL []; SQL state [null]; error code [0];

Mysql tinyint is toxic​

mysql do not use field type tinyint, possibly your update of 1 will become 49

See blog

MybatisPlus Invalid bound statement (not found) exception​

See article

idea terminal Chinese garbled characters​

Reference article

# solve idea terminal Chinese garbled
export LANG="zh_CN.UTF-8"
export LC_ALL="zh_CN.UTF-8"

Other Problems​

Dynamic Data Source Problems​

If the operation used has a transaction, you need to set the data source before the Dao layer. In Dao or Mybatis-plus, service with dao will switch data source invalidly.

jackson serialization problems​

LocalDateTime not supported by default​

Java 8 date/time type java.time.LocalDateTime not supported by default:
add Module "com.fasterxml.jackson.datatype:jackson-datatype-jsr310" to enable
handling (through reference chain: java.util.ArrayList[0]->xxx.xxx.xxx.xxx.XxxxPo["updatetime"])

First troubleshoot where it is reported

  1. If Spring Boot can be extended: directly extend ObjectMapper
@Configuration
public class JacksonConfig implements WebMvcConfigurer {
    @Override
    public void extendMessageConverters(final List<HttpMessageConverter<?>> converters) {
        MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);
        objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        objectMapper.registerModule(new JavaTimeModule());
        messageConverter.setObjectMapper(objectMapper);
        converters.add(0, messageConverter);
    }
}
  1. If cannot extend, consider skipping Bean serialization step, such as using method to convert Bean to Map
  2. If really no way, use Fastjson or Gjson instead

Second field uppercase problem​

  1. Use @JsonProperty

@JsonProperty is used to explicitly tell Jackson:

"This field (or method, constructor parameter) is to be used as a JSON property, and the property name is XXX."

  1. Use @JsonAutoDetect
@JsonAutoDetect(
fieldVisibility = JsonAutoDetect.Visibility.ANY,
getterVisibility = JsonAutoDetect.Visibility.NONE,
setterVisibility = JsonAutoDetect.Visibility.NONE)

Members used in serialization and deserialization

Usage LocationInfluence DirectionCommon Usage
FieldSerialization + DeserializationForce include private fields
getterSerializationChange output field name
setterDeserializationChange input field name
Constructor ParameterDeserializationMap JSON parameter name to constructor parameter
record ParameterSerialization + DeserializationControl JSON property name

Database Connection Pool Configuration Problems​

When using Druid connection pool, config parameter validationInterval must be less than timeBetweenEvictionRunMillis, ensuring database connection is always available.

API Interface Standards​

  • Query data volume
  • Input parameter check
  • Response message large integer, floating point fields use string type
  • Input parameter type not primitive type
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