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Chapter 1 Introduction
to the course The original intention of making this course, my positioning and vision for this course, what content is included in the course, what can help you, and how to learn this course, in order to better digest and absorb.
Why do this course 1-1 Look
1-2 Why do we need every one of your
1-3 sentiment addition, you can also have plagued this
Chapter 2 Java and null pointer exception - often guilty Index 5 stars
null pointer issues and Various common exceptions (concurrent modification, type conversion) are almost the most troublesome problem for all Java beginners. This chapter will teach you how to avoid these problems, how to use Optional to avoid the null pointer problem, and correctly use try catch to catch exceptions
2-1 How to avoid null pointers from the root cause?
2-2 Null pointers are automatically unboxed when assigning values
2-3 Null pointers appear when strings, arrays, and collections are used?
2-4 What should I pay attention to when using Optional?
2-5 Obviously try catch but the exception is not resolved?
2-6 Common Exceptions: Concurrent Modification, Type Conversion, Enumeration Lookup
2-7 Solutions to Common Exceptions in Coding
2-8 Use Try Finally Resource Leakage Potential
Chapter 3 Java Calculations, Collections, Interfaces-Frequent Offence Index 4 stars
no matter what Business development is inseparable from the use of calculations and collection data structures. Frequent errors caused by frequent use are obviously unacceptable. This chapter will let you see the most common errors and solutions; beginners often confuse interfaces and Abstract classes, especially after Java 8 adds default and static methods, this situation is even more serious. This chapter will teach you how to use and understand them correctly...
3-1 BigDecimal error? It's all precision pot
3-2 Why do you always use bad date calculations?
3-3 Reasons for the thread insecurity of SimpleDateFormat
3-4 I just want to iterate the elements, no index is needed.
3-5 Nested iteration, be careful of the premature exhaustion of the outside!
3-6 If it is not good to judge and wait, the collection storage will be
messed up. 3-7 Using lombok annotations, what should I do if it does not meet expectations?
3-8 How to avoid mistakes in choosing abstract classes and interfaces?
3-9 The default method and static method rewriting of the interface is always not as expected?
3-10 lambda expressions can not be written anywhere
3-11 lambda and Stream are really efficient?
Chapter 4 Generics, Reflection, Compiler Optimization-Frequently Offensive Index 3-star
Generics and reflection are both advanced features of the Java language. Beginners are prone to cause various exceptions and problems. This chapter takes you to analyze, understand and learn to use these advanced features ; Although the compiler will optimize our code, it is not always reasonable. Therefore, we cannot rely on the optimization of the compiler. This chapter will also take you to analyze this problem...
4-1 If the parent class does not implement Serializable, can the subclass not be implemented?
4-2 What should I do if an error is reported after implementing the Serializable interface?
4-3 Generics are not just as simple as specifying the types in the collection.
4-4 Generic features you must know.
4-5 Using primitive types can have catastrophic consequences. See
4-6. Reflection is also flawed.
4- 7 Why can't reflection get Method?
4-8 Not all string concatenations use StringBuilder.
4-9 The answer is to copy in dark and shallow during the interview. Will it be used in practice?
4-10 Does your serialization implement deep copy or shallow copy?
Chapter 5 Java Thread Safety-Frequently guilty index of 3 stars.
About thread safety, multithreading, etc., it can be said that it has stumped a large number of Java beginners. The reason for this is that there is no idea and no way to break this. A kind of knowledge points, this chapter will take you to appreciate the charm of thread safety and multithreading, and let you learn to use them correctly and reasonably.
5-1
Ca n't use Synchronized keywords well 5-2 How to update variable values in multi-threaded mode
5-3 When it comes to blocking queues, do you feel confused
5-4 It is not always suitable to use Copy-On- Write
5-5 uses the thread pool, have you ever encountered an execution rejection exception?
5-6 Thread pool is actually a tool used to manage threads
5-7 How to monitor thread status?
5-8 ThreadLocal is not used to solve concurrency or sharing problems.
5-9 If ThreadLocal is not used well, memory leaks are very likely to occur
. Chapter 6
Pitfalls in Spring For those who are new to Spring, it is not a problem to be able to use Spring well. Easy things, there are endless questions about Bean name, automatic injection, understanding of container and context, scope, circular dependencies, transactions, etc. This chapter will take you to understand Spring's features, understand and use Spring well.
6-1 Spring configuration files should be careful "one step"
6-2 Do you know the default name generation strategy of Spring Bean?
6-3 The @Autowired annotation is used, but a null pointer still appears.
6-4 Can you still get the context without using automatic injection? (Top)
6-5 Will you still get context without using automatic injection? (Next)
6-6 Bean data does not meet expectations, what should I do?
6-7 Do you often report "There are multiple available beans" exception? (Top)
6-8 Do you often report "there are multiple beans available" exception? (Next)
6-9 Spring Bean has circular dependencies, what should I do?
6-10 What can we do before the bean is instantiated?
6-11 Learn to use the life cycle of Beans to get twice the result with half the effort
6-12 Is your @Transactional mark in the right position?
6-13 Can't roll back after @Transactional?
Chapter 7 Pitfalls in SpringMVC I
believe you must have encountered problems with response codes, serialization and deserialization, and you may not be able to distinguish the difference between interceptors and filters, how to use them, and the flow of reading The methods that appear in the process are mutually exclusive. This chapter will guide you to understand these characteristics and avoid common misuses.
7-1 Do you always fail to understand other people's custom anomalies?
7-2 It is obvious that a custom exception should be thrown, how can it report 500?
7-3 The time format cannot be converted normally? Check the POST request.
7-4 Is the time format local processing really good?
7-5 Can't enter the breakpoint during debugging? It may be that multiple Fliters are stuck in the
7-6 log. Should the log be placed in the interceptor, or the filter
7-7 reads the Request input stream, and the request data is gone.
7-8 Can't get the data? It may be a pot of mutually exclusive methods.
Chapter 8. The pit in
SpringBoot SpringBoot depends on configuration, but have you figured out the priority of configuration? Timed tasks and asynchronous tasks are very simple to write, but how to troubleshoot and solve problems that occur? How much do you know about the default Jackson tools? This chapter will take you to use these features and knowledge points correctly
8-1 The configuration is always wrong? Are .properties and .yml used at the same time?
8-2 Is it invalid if the configuration is changed to another location? Find out the order of loading.
8-3 The timing task is irregular. What's wrong?
8-4 Can't see the reason for the lack of thread pool? It may be that the asynchronous task has not been handled properly.
8-5 What should I do if the asynchronous task has timed out?
8-6 The speed is slow, have you ever thought that ObjectMapper may be instantiated too many times?
8-7 What is the difference between Jackson and fastJson?
Chapter 9 Pitfalls in MySQL
Beginners must be able to understand and use data types, indexes, and transactions correctly. These are the most basic characteristics of a database, and then gradually advance to slow query optimization, learning to sub-databases and tables, etc., this chapter Follow me to learn and understand these knowledge points
9-1 Set the table attribute to NULL, you may have to face a lot of trouble
9-2 No longer set the data type randomly, so as not to leave hidden dangers in the future
9-3 Index addition is not good, the effect may be counterproductive (
Part 1) 9-4 Index addition The effect is not good, the effect may be counterproductive (below)
9-5 Why does MySQL disconnect inexplicably
? 9-6 Transaction processing error? It may be that the lock is used incorrectly
9-7 The SQL you write may be very slow, how to optimize it?
9-8 As the amount of data gradually increases, is it feasible to consider sub-databases and tables?
The
caching of pit key-value pair types in Chapter 10 Redis seems very simple, but how to choose the right data structure is not a simple matter; in the process of using, also consider performance, memory optimization, and data persistence It sounds even more difficult to deal with issues such as transformation, cache penetration, and avalanche. However, this chapter will take you to understand and overcome these problems and knowledge points one by one...
10-1 How to choose the data type correctly, so that maintenance is no longer a nightmare
10-2 The transaction function is used, why is it not rolled back?
10-3 Redis performance does not improve, maybe there is a big key
10-4 Why does Redis run out
of memory? 10-5 What should I do if the memory is not enough after the expiration mechanism?
10-6 How to solve the performance bottleneck caused by frequent command round trips?
10-7 Have you configured the persistence mechanism?
10-8 Does your code have cache penetration risks?
10-9 What should I do if there is a cache avalanche? How to avoid it?