java.lang.NoClassDefFoundError: java/util/Base64

Problem

In the following code, Base64 is used to encode AES encrypted data bytes to plain text for transfering via URL query parameter.

 

But when running this code on my coworker’s machine, following exception is thrown

 

It’s because that my execution environment is Java 8, but my coworker is using Java 7, and java.util.Base64 is introduced in Java 8.

 

Solution

To fix this issue, we can use Base64 class from Apache Commons Codec.

First add commons codec dependency to maven pom.xml file.

Next import Base64 class from commons-codec

 

Finally replace  Base64.getUrlEncoder().encodeToString to Base64.encodeBase64URLSafeString .

So the code will become like following

 

 

Method.invoke throws java.lang.IllegalArgumentException: wrong number of arguments

Background

There is a private downloadFile method of ZhangyoobaoLeshuaMerchantRegister class, the method signature is like following

A unit test case for this method need be created, in this test case we need pass a null value as parameter to test whether this method can handle null parameter. But a private method cannot be accessed from the instance level. The solution is to use reflection to get the method, and set its accessiblity to public temporarily (by using the Method.setAccessible method).

 

First let’s see some code

Above Java code is the unit test case, it uses reflection to get the private method downloadFile of class ZhangyoobaoLeshuaMerchantRegister, and set the access level of this method to public, then call it with parameters. (Note that if setAccessible is not called to set method access level, Method.invoke will throw IllegalAccessException.)

But running this line  result = method.invoke(register, null);  will got following error

It’s because the second argument of Method.invoke() is Object...  (An Object[] array), its elements are arguments passed in to the method. Calling Method.invoke() with null as second argument is actually trying to call the method with no arguments, but downloadFile method requires one parameter, so it definitely raises IllegalArgumentException.

 

Solution

To fix this issue, change following line

to

This will pass null as first argument for downloadFile method. new Object[]{null}  is correspondding to the Object...  argument of Method.invoke(), it’s expanded like calling downloadFile(null) .

 

Hibernate Query unexpected token: INTERVAL

I’m trying to fetch inventories which is opened at last month, for traditional SQL DATE_SUB function should be used here for date calculation. So the HQL is like following

 

But following error appeared when running it in Hibernate QL Query Consonle in Intellij IDEA

 

Unfortunatelly the INTERVAL keyword is not supported in HQL.

 

Solution

An alternative is to calculate the date in Java and pass the result dates to HQL as parameters. The code is like following

 

Implementation code for DateUtil.getLastMonthFirstDay and DateUtil.getLastMonthLastDay

 

 

 

GitLab took too much memory

The gitlab execution on our company internal server eats lots of memory, the server has 32G memory, and gitlab took more than half of it.

 

I found there are lots of unicorn processes running, and each unicorn process is taking 1.5% memory
In top  command output it’s displaying as ruby process and took nearly 500MB resident memory (by default top is sorting by cpu usage, pressing < or > key to change sorting column)
Running above command outputs 34, that means at most 34 unicorn processes are running (some other processes’ name also contain unicorn)..
Assume there are 30 real unicorn process running, each takes 500MB memory, then they will take 30*500MB=15GB memory
To decrease unicorn processes count, edit /etc/gitlab/gitlab.rb, and uncomment following line

 

Next restart GitLab

Now the memory usage is decreased.

 

(Note that running gitlab-ctl reconfigure  will not kill already running unicorn processes)

CentOS 6 Install netcat

Netcat is one utility in NMap toolset, it maybe named as nc, ncat or netcat on different Linux distributions. (It’s ncat on CentOS 6).

On CentOS 6 netcat is not installed by default, to install it we can run following command

 

Then run following command to check netcat is installed correctly

 

Cannot install Docker on CentOS 6

Installing docker-ce on CentOS 6.9 got following error

 

To install docker on CentOS 6, run the following command

 

Then run

Its output is

Docker version 1.7.1, build 786b29d/1.7.1

 

We can see docker is installed successfully.

Spring Cloud Zuul Ribbon custom rule not working

I need a custom Rule which can route requests to different service according to weight option (actually I want to deploy an A/B test service and only small percent of user will hit it), the code is like following

 

And following is application.yml configuration file

 

Adding breakpoints at constructor of ZoneAwareLoadBalancer and DynamicServerListLoadBalancer, then access the Zuul service via browser and I found ZoneAwareLoadBalancer constructor breakpoint is reached first.

Inspect the value clientConfig->properties->NFLoadBalancerClassName, its value is still “com.netflix.loadbalancer.ZoneAwareLoadBalancer”, and the passed in rule is not my configured rule as well.

This means my configuration didn’t work.

 

Even I changed the class name to an invalid value, there is no error

 

In Spring Cloud documentation, under Customizing the Ribbon Client using properties section, it’s saying

Starting with version 1.2.0, Spring Cloud Netflix now supports customizing Ribbon clients using properties to be compatible with the Ribbon documentation.

Checking maven pom file I found it’s using 1.1.0

 

Changing them to 1.2.0 and run again, following exception is thrown

 

It’s because NFLoadBalancerRuleClassName is aaa, changing it to a valid name and try it again, it works now

 

 

Docker SSH set password not working

First run passwd  command to change the password, after inputting new password, following output is shown.

passwd: password updated successfully

I bind docker port 22 to host port 33333, then running following command to connect to it using ssh with the new password we set earlier

After inputing password, following error is appeared

Permission denied, please try again.

SSH logs from /var/log/auth.log

Solution

To fix this issue, change /etc/ssh/sshd_config

to

Restart sshd and connect to it again, it should work now.

Specified key was too long; max key length is 3072 bytes

 

When running above statement to add unique index, following error happened.

[2018-03-28 11:38:24] [42000][1071] Specified key was too long; max key length is 3072 bytes

 

Table structure

So the above index key length is value(255*3), productId(4), productName(255*3), productSerialNumber(255*3), userPhone(255*3), userName(255*3), userId(8), type(255*3), statStartTime(8), statEndTime(8)

Total length is 255*6*3 + 4 + 8*3=4618 is greater than 3072 bytes.

 

Note that the charset used is UTF8, so every character will occupy 3 bytes.

 

Solution

Then change to following statement, and the error is fixed.

 

Another solution is to increase this 3072 bytes limit.

Intellij IDEA plugin development get selected text

To get selected text in a Intellij Platform Plugin project, we can use following code

 

The first line is used to get current editor object

 

Then call getSelectionModel and getSelectedText method to get selected text

 

The last two lines is to to some operation for selected text, it’s unrelated to our goal.