I don't know how lucky the boy who randomly typed logs is. There must be a lot of overtime

Preface

There's a problem online , What was your first reaction ？

If I were you , The first thought should be to check the log ：

1. if…else Which branch did you enter ？
2. Are the key parameters missing ？
3. Is there a problem with participation , I didn't check it well and put it in ？

A good log can help us quickly locate the problem , The thing that pits you is often the most invisible , A good log is to make these things invisible ！

The level of logging

Java Application , Logs are generally divided into the following 5 A level ：

• ERROR error message
• WARN Warning message
• INFO General information
• DEBUG Debugging information
• TRACE Tracking information

1）ERROR

ERROR Level logs are generally catch Inside the block , Used to record errors that affect the normal operation of the current thread , appear Exception Where you can consider printing ERROR journal , But it does not include business exceptions .

It should be noted that , If you throw an exception , Don't record ERROR Log , It should be dealt with in the final place , This is wrong ：

try {
    int i = 1 / 0;
} catch (Exception e) {
    log.error(" Something went wrong , I don't know what's wrong , Ah ha ha ha ！", e);
    throw new CloudBaseException();
}
 Copy code 

2）WARN

Not supposed to show up , However, if it will not affect the execution of the current thread, you can consider printing WARN Level of logging , There are many such situations , such as ：

• All kinds of pools （ Thread pool 、 Connection pool 、 Buffer pool ） The use of exceeds the threshold , Reach the alarm line
• Record business exceptions
• There was a mistake , But the fault-tolerant mechanism is designed , So the program can run normally , But it needs to be recorded

3）INFO

The most used log level , It's widely used , It is used to record the operation information of the system , such as ：

• The logical steps in important modules are presented
• Client request parameter record
• Parameters and return structure when calling the third party

4）DEBUG

Debug Logs are used to record all the information you want to know , It is often the details of the operation of a function module , The data has changed in the middle , And performance information .

Debug Information is generally off in the production environment , Switch management is required （ such as SpringBoot Admin It can be done ）, Opening it all the time will produce a lot of Debug, and Debug Logs are useless most of the time when the program is running normally .

if (log.isDebugEnabled()) {
    log.debug(" Start execution , Starting time :[{}], Parameters :[{}]", startTime, params);
    log.debug(" By calculation , Get parameters 1:[{}], Parameters 2:[{}]", param1, param2);
    log.debug(" Finally, the result is processed :[{}]", result);
}
 Copy code 

5)TRACE

Special detailed system operation completion information , Generally, it is not used in business code , Unless it has special significance , Otherwise, it is generally used DEBUG Instead of , in fact , I've been coding until now , I have never used this level of log .

Use the correct format

If you print the log like this ：

log.info(" According to the condition id：{}" + id + " Query user information ");
 Copy code 

Don't do this , A large number of string objects will be generated , Taking up space will also affect performance .

The correct way is to use parameterized information ：

log.info(" According to the condition id：[{}], Query user information ", id);
 Copy code 

In addition to avoiding creating a large number of strings , It can also clearly isolate parameters , When you need to copy the parameters , Just double click the mouse , Instead of slowly aiming at it with the mouse and then drawing it .

The log printed like this , High readability , It is also very helpful for troubleshooting problems ！

Tips

1） Multithreading

How to log when multiple threads execute together ？

Some systems , Involves concurrent execution , Scheduling, etc , There will be multiple execution logs mixed together , It's not easy to find out if something goes wrong , We can print the thread name , Or add an identifier to indicate which execution this log belongs to ：

if (log.isDebugEnabled()) {
    log.debug(" perform ID=[{}], Processed ID=[{}] The news of , Processing results ：[{}]", execId, id, result);
}
 Copy code 

2） Use SpringBoot Admin Flexible switch log level

At the end

At the beginning of writing code , There is no consciousness of standardizing logs , No matter where , All of them INFO, I haven't thought about what I printed , Does it make sense , In fact, I stepped on many pits , Many extra classes , Look back , I want to say something to me during my study ：” Things that can make you work overtime , All hidden in various details ！ Before writing the code , First, learn how to log ！“