Category Archives: JAVA

Android Studio Cannot resolve symbol [How to Solve]

Problem:
Previously the project is normal, one day suddenly appeared red exception, the code is prompted in many places “Cannot resolve symbol xxxx” Log

Analysis:
The problem is caused by the failure of the three-party library dependency, the guide package can not be found

Solution (you can follow the following process to try):
1, Build->Clean Project and then Build->Rebuild Project to see if it is OK, not continue
2,File->Sync Project With Gradle Files to see if it’s OK, if not, continue
3,File->Invalidate Caches/Restart (check Clear Cache or Files) to see if it’s OK, or not.
4, close AS, manually enter the project to delete the .gradle and .idea files, reopen AS build to see if it is OK, not continue
5, downgrade the AS version, keep the settings and uninstall the current version, download and install the old version without problems before

The above five steps will basically solve the problem, which step is OK, just follow the order.
My problem is to the fifth step, from AS Bumblebee directly downgrade to AS4.2.1 before the problem is solved, the middle of the Arctic fox also have problems, specifically ignore.

Translated with www.DeepL.com/Translator (free version)

How to Solve the Primary Key of mybatisPlus Inserted Data is too Large Issue

Solve the problem that the primary key of mybatisplus inserted data is suddenly large

1. Enter the corresponding database in the administrator window, and then enter the following instructions:

alter table sys_user AUTO_INCREMENT=30;

​sys_user is the name of the data table to be modified, and 30 is to modify the self increment starting value to 30

In this way, the primary key value of the data table will return to normal

2. In the entity class of the project, add a @Tableid annotation to the primary key of the class

package baocms.entity;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName(value = "sys_user")
public class User {
    @TableId(value = "id",type = IdType.AUTO)
    private Integer id;
    private String username;
    private String password;
    private String nickname;
    private String email;
    private String phone;
    private String address;
}

How to Solve c3p0 error (Cause & Solution)

Error Cause & Solution:
1. Configuration is wrong: driver=com.mysql.jdbc.Driver.
2. Wrong database connection address: url=jdbc:mysql://localhost:3306/test (test is user-defined creation, variable).
3. Wrong password or account: username=root (default is root).
4. Wrong account: password=root (password is set by the user).
5. The database is not started or not authorized to access.
6. The corresponding driver jar package mysql-connector-java-5.1.6-bin.jar has not been introduced, or the mysql-connector-java dependency has not been injected in the Maven project.

IDEA Import Servlet Package Error [How to Solve]

When we use idea to import packages related to servlets, we sometimes encounter errors, which leads to the problem that servlets cannot recognize. In fact, the reason for the problem is very simple, that is, we can’t find packages related to servlets in JDK

Solution:
1. Find the installation directory of Tomcat, here is C:\Program Files\Apache Software Foundation\Tomcat 8.5\lib (Note: not everyone’s directory is this, need to be based on the actual situation of your computer’s installation directory), find the Servlet-api.jar This file, copy it

2. then go to the JDK installation directory: C:\Program Files\Java\jdk1.8.0_241\jre\lib\ext, find the ext folder, and then copy the Servlet-api.jar file just copied to this folder

3. Back to the idea, the problem is solved, if the idea is still reporting errors, restart the idea refresh

[Solved] IDEA2020 Error: Cannot resolve symbol ‘Servlet‘

Reason: no servlet-api.jar package

I tried all the methods on the Internet and found that it was the problem with my servlet-api.jar package

It was not placed under the Lib package of tomcat9. Another one was downloaded online and placed on disk D

Solution:

Right-click item — Open Module Settings

Libraries – + — Java – — find servlet-api.jar package, add it to the project, and click apply

How to Download File via Response (Example Code)

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Here is an example code for you to use Response to download files.

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // 1.Get the file path
    String realPath = "D:\\project\\\servlet-main\\\\response\\\src\\\main\\\resources\\\\avatar.jpg";
    // 2. Get the file name
    String fileName = realPath.substring(realPath.lastIndexOf("\\\") + 1);
    // 3. Set the request header (Content-Disposition of the header to support file download)
    resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
    // 4. Get the input stream of the downloaded file: FileInputStream
    FileInputStream inputStream = new FileInputStream(realPath);
    // 5. Create buffer
    int length = 0;
    byte[] buffer = new byte[1024];
    // 6. Get the input stream object: OutputStream
    ServletOutputStream outputStream = resp.getOutputStream();
    // 7. Write the stream to the buffer and use the OutputStream to output the data in the buffer to the client
    while ((length = inputStream.read(buffer)) > 0) {
        outputStream.write(buffer, 0, length);
    }
    inputStream.close();
    outputStream.close();
}

[Solved] Error running ‘ServiceStarter’: Command line is too long. Shorten command line for ServiceStarter or also for Application default configuration

1. Question

IntelliJ idea command line is too long solution
error content:
error running 'servicestarter': command line is too long Shorten command line for ServiceStarter or also for Application default configuration.

2. Solution

Modify item .idea\workspace.xml, find the tag and add a line to the tag

<property name="dynamic.classpath" value="true" />

How to Check the appPackage or appActivity of an APK

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Here is a simple guide on how to check the appPackage and appActivity in apk.

 

How to Check the appPackage or appActivity of an APK

Option 1:

  1. aapt dump badging xxxx.apk
  2. Lookup “package: name” and “launchable-activity: name” in terminal’s output

Option 2:

  1. java -jar apktool_2.3.3.jar d xxxx.apk
  2. Lookup appPackage and appActivity in AndroidManifest.xml

[Solved] org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘org

error

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2022-02-26 14:30:30.017 ERROR 13724 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.cloud.netflix.archaius.ArchaiusAutoConfiguration': Unsatisfied dependency expressed through field 'externalConfigurations'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'configurableEnvironmentConfiguration' defined in class path resource [org/springframework/cloud/netflix/archaius/ArchaiusAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.cloud.netflix.archaius.ConfigurableEnvironmentConfiguration]: Factory method 'configurableEnvironmentConfiguration' threw exception; nested exception is java.lang.NoClassDefFoundError: com/netflix/config/DeploymentContext$ContextKey
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:659) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:639) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:119) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:399) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1431) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:619) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:953) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.16.jar:5.3.16]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.16.jar:5.3.16]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.4.jar:2.6.4]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740) ~[spring-boot-2.6.4.jar:2.6.4]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415) ~[spring-boot-2.6.4.jar:2.6.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) ~[spring-boot-2.6.4.jar:2.6.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312) ~[spring-boot-2.6.4.jar:2.6.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) ~[spring-boot-2.6.4.jar:2.6.4]
	at com.atguigu.gulimall.product.GulimallProductApplication.main(GulimallProductApplication.java:25) ~[classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'configurableEnvironmentConfiguration' defined in class path resource [org/springframework/cloud/netflix/archaius/ArchaiusAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.cloud.netflix.archaius.ConfigurableEnvironmentConfiguration]: Factory method 'configurableEnvironmentConfiguration' threw exception; nested exception is java.lang.NoClassDefFoundError: com/netflix/config/DeploymentContext$ContextKey
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:658) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:638) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1352) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1195) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.addCandidateEntry(DefaultListableBeanFactory.java:1607) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1571) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveMultipleBeans(DefaultListableBeanFactory.java:1460) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1347) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1309) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:656) ~[spring-beans-5.3.16.jar:5.3.16]
	... 20 common frames omitted
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.cloud.netflix.archaius.ConfigurableEnvironmentConfiguration]: Factory method 'configurableEnvironmentConfiguration' threw exception; nested exception is java.lang.NoClassDefFoundError: com/netflix/config/DeploymentContext$ContextKey
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.3.16.jar:5.3.16]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:653) ~[spring-beans-5.3.16.jar:5.3.16]
	... 36 common frames omitted
Caused by: java.lang.NoClassDefFoundError: com/netflix/config/DeploymentContext$ContextKey
	at org.springframework.cloud.netflix.archaius.ArchaiusAutoConfiguration.configureArchaius(ArchaiusAutoConfiguration.java:122) ~[spring-cloud-netflix-archaius-2.1.2.RELEASE.jar:2.1.2.RELEASE]
	at org.springframework.cloud.netflix.archaius.ArchaiusAutoConfiguration.configurableEnvironmentConfiguration(ArchaiusAutoConfiguration.java:109) ~[spring-cloud-netflix-archaius-2.1.2.RELEASE.jar:2.1.2.RELEASE]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
	at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.3.16.jar:5.3.16]
	... 37 common frames omitted

 

Solution:

Compared with other similar services
it is found that

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
<!--            <version>2.2.7.RELEASE</version>-->
        </dependency>

The version of openfeign is redundant and can be run after being commented out

[Solved] ERROR SparkContext: Error initializing SparkContext. java.lang.IllegalArgumentException: System memo

During the actual operation of the recommendation system, the following errors occur when executing the featureengineering (Scala) file:
ERROR SparkContext: Error initializing SparkContext. java.lang.IllegalArgumentException: System memory 259522560 must be at least 471859200

Solution:
1. Click Edit configurations

2 If your setting interface has the following red box, paste the following text directly

-Xms128m -Xms512m -XX:MaxPermSize=300m -ea


3. If not, click Modify options first, then add VM options, as shown in the figure below, and then complete the second step

this problem should be solved.

[Solved] Feign Call Port Error: HttpMessageNotReadableException：JSON parse error：Illegal character ((CTRL-CHAR, code 31)

Background

In a timed task, the remote interface is called every hour for data synchronization. At first, the implementation method was to call the remote interface in a loop and pass in a single record each time, because each time we need to complete the operation of establishing a connection, data transfer, and disconnection, which is more expensive network and connection resources; later, after testing no problem, we changed to pass in a list for bulk operation after the loop is completed, and then the problem appeared.

10: 12:28.881 [http-nio-8200-exec-3] error c.y.c.s.h. globalexceptionhandler – [handleruntimeexception, 82] – Request Address’/doit ‘, unknown exception occurred org. springframework. http. converter. HttpMessageNotReadableException: JSON parse error: Illegal character ((CTRL-CHAR, code 31)): only regular white space (\r, \n, \t) is allowed between tokens; nested exception is com. fasterxml. jackson. core. JsonParseException: Illegal character ((CTRL-CHAR, code 31)): only regular white space (\r, \n, \t) is allowed between tokens

Environmental information

Version information of openfeign :

Problem analysis

feign is configured as follows:

# feign
feign:
  sentinel:
    enabled: true
  okhttp:
    enabled: true
  httpclient:
    enabled: false
  client:
    config:
      default:
        connectTimeout: 10000
        readTimeout: 10000
  compression:
    request:
      enabled: true
    response:
      enabled: true

From the configuration, we can understand that the current configuration enables the request and response compression function. We know that when the compression is actually related to the size of the request body, if the requested data body itself is small, it can be transmitted directly without compression, which can save CPU resources for compression; there is a possible reason: compression is a threshold value, more than a certain threshold will be compressed. This can explain the previous question: why is it OK to transfer one piece of data at a time, but there is an error when transferring the list?

 

Solution:

Just turn compression off.

Note: Due to the change to bulk transfer, the business processing takes longer and errors like “Timed out…” may appear at the request initiation side. The configuration here changes the timeout of HTTP connection from 10s to 60s; when the data synchronization is finished, change it back.