Java笔记(2020)

1. 复杂JSON字符串转模型

1 import com.fasterxml.jackson.core.type.TypeReference;
2 import com.fasterxml.jackson.databind.ObjectMapper;

1 ObjectMapper mapper = new ObjectMapper();
2 List<CustomModel> list =  mapper.readValue(json, new TypeReference<List<CustomModel>>() { });

2. 在非Bean对象调用Spring Bean管理的对象

 1 package com.wunaozai.demo
 2 
 3 import org.springframework.beans.BeansException;
 4 import org.springframework.context.ApplicationContext;
 5 import org.springframework.context.ApplicationContextAware;
 6 import org.springframework.stereotype.Component;
 7 
 8 /**
 9  * 为不是spring所管理的对象,需要引用spring管理对象的时候所用的工具类
10  * @author wunaozai
11  *
12  */
13 @Component
14 public class SpringApplicationContext implements ApplicationContextAware {
15 
16     protected static ApplicationContext context;
17     
18     @Override
19     public void setApplicationContext(ApplicationContext ctx) throws BeansException {
20         context = (ApplicationContext) ctx;
21     }
22 
23     public static ApplicationContext getContext(){
24         return context;
25     }
26     
27 }

调用

1 CustomerService influxdbconnectService = SpringApplicationContext.getContext().getBean(CustomerService.class);

3. Spring Boot 项目出现 pom.xml 第一行莫名的错误，在pom.xml 的 properties段下增加

1 <maven-jar-plugin.version>3.0.0</maven-jar-plugin.version>

4. eclipse maven 更换阿里源，需要配置 settings.xml 文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <settings>
 3     <mirrors>
 4         <mirror>
 5             <id>alimaven</id>
 6             <name>aliyun maven</name>
 7             <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
 8             <mirrorOf>central</mirrorOf>
 9         </mirror>
10     </mirrors>
11   <profiles>
12     <profile>
13        <id>nexus</id>
14         <repositories>
15             <repository>
16                 <id>nexus</id>
17                 <name>local private nexus</name>
18                 <url>http://maven.oschina.net/content/groups/public/</url>
19                 <releases>
20                     <enabled>true</enabled>
21                 </releases>
22                 <snapshots>
23                     <enabled>false</enabled>
24                 </snapshots>
25             </repository>
26         </repositories>
27          
28         <pluginRepositories>
29             <pluginRepository>
30             <id>nexus</id>
31             <name>local private nexus</name>
32             <url>http://maven.oschina.net/content/groups/public/</url>
33             <releases>
34                 <enabled>true</enabled>
35             </releases>
36             <snapshots>
37                 <enabled>false</enabled>
38             </snapshots>
39             </pluginRepository>
40         </pluginRepositories>
41     </profile></profiles>
42 </settings>

5. spring boot 项目，用maven编译打包时，使用wrapper时遇到下载apache-maven失败，可以到 .m2/wrapper/dists/apache-maven-** 目录下，将离线包放到该目录下。或者修改wrapper目录下的maven-wrapper.properties文件里面的distributionUrl 为本地离线地址，都是可以的。

6. mybatis-plus 打印SQL详细日志，在application配置文件中增加

1 #mybatis-plus
2 mybatis-plus.mapper-locations=classpath:com/wunaozai/demo/mapper/*.xml
3 mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

7. springboot中默认使用jackson做json序列化和反序列化，后台接收数据时将上述日期字符串转成LocalDateTime时，会报如下错误

JSON parse error: Cannot deserialize value of type java.time.LocalDateTime from String “2018-09-20 08:01:00”: Failed to deserialize java.time.LocalDateTime: (java.time.format.DateTimeParseException) Text ‘2018-09-20 08:01:00’ could not be parsed at index 10; nested exception is com.fasterxml.jackson.databind.exc.InvalidFormatException: Cannot deserialize value of type java.time.LocalDateTime from String “2018-09-20 08:01:00”: Failed to deserialize java.time.LocalDateTime: (java.time.format.DateTimeParseException) Text ‘2018-09-20 08:01:00’ could not be parsed at index 10

解决办法：

导入jackson-datatype

1         <dependency>
2             <groupId>com.fasterxml.jackson.datatype</groupId>
3             <artifactId>jackson-datatype-jsr310</artifactId>
4         </dependency>

配置bean

 1     @Bean
 2     public ObjectMapper serializingObjectMapper() {
 3         JavaTimeModule module = new JavaTimeModule();
 4         LocalDateTimeDeserializer deserializer =
 5                 new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
 6         module.addDeserializer(LocalDateTime.class, deserializer);
 7         ObjectMapper object = Jackson2ObjectMapperBuilder.json()
 8                 .modules(module)
 9                 .featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
10                 .build();
11         return object;
12     }

持续更新...