How to read the source code [debug and observe the source code]

author : Yilele
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* Compiler knowledge required for reading source code ( Compiler is eclipse As an example ）

• Commissioning preparations （ step ：Window -> Show View -》...）：

  □ Open debug breakpoint Breakpoint：

  □ Turn on variable monitoring

• It depends on the internal details of a method , Press f5, Get into

• Jump to a certain position quickly 【 Make a breakpoint at the target location 】, Then press f8

• Details of the observation method （ Execute the process ）, Step by step , Press f6

• Remove all breakpoints （ The compiler is eclipse）

  □ Pay attention to whether the execution position of the start tag is correct

• f5 Enter by debugging 【 If the entry is irrelevant , Press f7 return , Press again f5 Enter once 】 give an example ：

User user = mapper.get(1L); // Make a breakpoint here to enter , Will enter first Long class , Because the order of execution is （1L） Execute first , So after entering it first , Re execution get Method 

• Press ctr and As debugged f5 The difference between ： □ ctr： Is to enter “ The selected code ( class 、 Interface 、 Method )” The location of the definition of 【 The emphasis is Definition of code 】 □ f5： It is to execute the current code in the order of execution , Get into 、 Execute its internal 【 The emphasis is Execution of code 】

• Press ctr With the mouse , You can know the next step of the code （ Press ctr Details to pay attention to ：ctr The default entry is the definition of the selected code , Not an implementation process , After entering, I found that I didn't see any helpful code , return Return press and hold ctr, Selective implementation （ If there are multiple implementations , I don't know which one to choose , It can be debugged f5 Get into ）, Press the mouse again to enter .

• Restart debugging details ： （1） Close the last debugging （2） Click on Before commissioning , Keep the... In front of the breakpoint at the start position √, Before other breakpoints √ Remove first （ Start debugging before √ Come back ）

• After entering a method, learn the details of the method , Want to go back and then proceed , Press f7 return 【 Back to press f7】 Generally, after in-depth understanding of a module , You can press return , return ... Then move on to the next module

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* The idea of reading source code

1、 Focus on understanding the execution logic （ The execution process can be carried out as control Enter a method or class , Understand the next step after , The cursor returns to the current position 【 Shortcut keys are alt+←】）

2、 Look at the source code process to clarify ideas , Abnormally related (error、exception、throw), The details that make the code more robust can be ignored ; Stack related stack, The bottom layer can be ignored

3、 In the code , See the selection Branch , You can observe the value of the variable ( Judge the condition ) Know which branch to enter

4、 In the code , See incomprehensible code , You can go down first , Then understand by observing the value of the variable 【 It can also be understood in combination with the official website 】

5、 Read stream 、 load resources 、 Binding namespace 、 Parameter conversion is not the point

6、 Constructing constructors is not the point , The point is to see The construction process of the constructor

7、 Constructing parsers is not the point , The point is to see The parsing process of the parser

8、 When you create a subclass, you should pay attention to ： What kind of subclasses ？ When a subclass has an encapsulated parent or sibling , Note what type of parent or sibling class is encapsulated ？

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* How to focus on reading source code （ With mybatis The source code of ）

■ 1、 The process of reading the source code , Which one should I read , Which is the key point of reading ？

• Read the source code to build the source code of the session factory object , I learned that ： Created a SqlSessoinFactory The session factory object is through the default SqlSessoinFactory Created , When creating, you need to pass in a configuration object 【 That is, when creating the session factory object, a configuration object is also created 】, thus , Study the creation process of configuration objects .

• Read the source code to build the source code of the session factory object , I learned that ： Create a sqlSession The session object is through the default sqlSession, You need to pass in three parameters when creating , The key is to observe which ？

□ configuration Configuration object （ I learned about it when I read the source code of session factory object construction , Is not the point ） □ executor actuator （ a key , Because in return The session object was previously built executor actuator ） □ autoCommit （ Submit or not , Boolean value , Is not the point ）

• Combine to understand logic , also return The hint of , Know that the key point of reading is list The process of

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* Words to master when reading the source code

• map mapping       mapper mapper
• factory factory
• build structure
• config To configure
• parse analysis     parser Parser      parsed Has been resolved      parseConfiguration Parsing configuration
• interceptor Interceptor
• plugin “ install [ enhance ]”、 plug-in unit
• proxy agent
• prepared precompiled callable Stored
• statment Statement object      preparedStatement Precompiled statement object     callableStatement Stored statement object
• cursor cursor
• instantiate Instantiation      instantiateStatement Instantiate the statement object
• handler processor      typeHandler Type processor
• row That's ok

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