Shulou(Shulou.com)06/02 Report--

This article focuses on "how to read Java source code", interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to read Java source code.

Initial contact of Java source code

If you have been developing for a year or so, you like to use eclipse's debug function. Well, you now have the technical foundation to read the source code.

I suggest starting with the JDK source code, which is directly integrated with eclipse and does not require any configuration.

You can start with JDK's toolkit, the Java version of "data structures and algorithms" we learned, such as List interface and ArrayList, LinkedList implementation, HashMap and TreeMap, etc. These data structures also involve sorting and other algorithms, killing two birds with one stone.

During the interview, the examiner always asks the difference between ArrayList and Vector. If you spend 10 minutes reading the source code, you will probably never forget it.

Then there are core packages, that is, String, StringBuffer, and so on.

If you have a basic knowledge of Java IO, you might as well read classes such as FileReader. I suggest you take a look at "Java In A Nutshell", which has an architecture diagram of the entire Java IO. Java IO class library, if you do not understand its interfaces and inheritance relationships, then reading is always confused.

The Java IO package, I think, is a case of elegant inheritance and interface application. If you work as an architect in the future, you will certainly deal with it frequently, such as core class development related to deployment and configuration in the project.

When reading these source codes, you only need to understand some core classes, such as 20 or 30 classes similar to ArrayList, and for each class, you don't have to understand every method. Some methods like String have reached the virtual machine layer (native method), such as the hashCode method.

Of course, if you are interested, you can compare the source code of JRockit, the same set of API, two implementations, very interesting.

If you want to drill again, take a look at the code for virtual machines, such as the principle of System ClassLoader, it is not in the JDK package, JDK is based on it. JDK's source code Zip package is only about 10m. It seems to have been downloaded by MJI Sun, but it is very secret. I was excited to find and read it for myself for a while.

Java Web development source code

Before reading Tomcat and other source code, there must be a certain amount of accumulation. From my practical experience, it can be said that the better ladder is:

1. I have written some Servlet and JSP code. Note that it's hard to get to the essence of Servlet without using Struts. Making good use of Struts is only superficial.

2. Read "Servlet and JSP Core programming"

3. Read the Servlet specification of Sun Company.

4. Read the packets of rfc,debug over http of http protocol.

If you have the above foundation, I do not recommend that you start reading the Tomcat source code. I suggest you read the Tomcat source code before reading the Struts source code. Struts source code is much simpler than WebWork source code. This framework is 100% readable, at least I don't understand WebWork at all. I once wrote a Struts framework because I understood the Web source code.

Of course, before reading the Struts framework, * has seen its MailReader and other demo, which is very good.

If you have done some Struts projects, it will be easier to read it.

Before reading Struts, it is recommended to take a look at the source code of mvnforum, which partially implements the function of Struts, although this BBS is not flattering.

If you've read Struts, start thinking about Tomcat source code reading.

However, I don't recommend reading it directly. Read the series "How Tomcat Works" on onJava, which is the simplest version of Tomcat. It tells you how HttpServletRequest is implemented inside the container, how Tomcat accepts external requests through Socket, and how your Servlet code is called by the Tomcat container (callback).

To learn JSP, be sure to read the Servlet source code compiled by the container JSP.

Why do I always call Tomcat a container, not a server? Leave this question to everyone.

If you must read Tomcat, then read Jetty. At least it is embedded, and the breakpoint debug can be set directly in eclispe. Although Tomcat also has an embedded version.

Java Database Source Code Reading

I suggest reading Sun's JDBC specification first.

I think you must have written the JDBC code, so you can start reading the source code at this time.

If you understand the JDBC specification (interface), then its implementation, JDBC Driver must begin to understand, my advice is to read mysql's jdbc driver, because it is open source, elegant design. When reading the JDBC driver source code of mysql, it is recommended to take a look at the inside story of mysql. There happens to be a book, "Mysql Internals", which I read five years ago. For example, you can know how mysql's JDBC driver interacts with the mysql server developed by C++ through socket packets (connect, query).

From the above reading, you can see how your business code, JDBC specification, JDBC driver, and database work together.

If you know these things, you will be comfortable learning persistence frameworks such as Hibernate and iBatis.

After reading the JDBC driver, be sure to read the database next. And there happens to be a powerful database developed in Java, Hsqldb. It is an embedded database, such as used in desktop client software, such as Mail Client.

Java communication and client software

I highly recommend instant messaging software wildfire and Spark. You can think of wildfire as a MSN server and Spark as a MSN client. They communicate through the XMPP protocol.

I once customized Spark in a project, including some server-side changes, of course. So I've read all their source code.

The reason I recommend them. Because:

1. XMPP is lightweight and easy to understand

2. Learn the implementation of Socket communication, especially the architecture design of CPX S

3. Modular design. They are all based on module, and you can understand both the modular architecture and the modular technical support: the application scenario of ClassLoader for the Java virtual machine.

4. Event Driven architecture. Although GUI is Event-driven, the design of Spark is particularly elegant

To put it this way, read their source code, and you will be proud to be a programmer, because both their architectural design and code are so beautiful.

Java enterprise application

Of course, there are frameworks like Hibernate and Spring.

Before reading the Spring source code, be sure to take a look at the "J2EE Design and Development" written by Rod Johnson, which is the design idea of Spring. Note that it is not the Chinese version, the Chinese version is completely spoiled.

Before reading the Hibernate source code, be sure to read the "Hibernate in Action" written by Gavin King. At the same time, you should read the "Enterprise Application Architecture pattern" written by Martin Fowler, which specifically talks about the design ideas of the persistence framework. When you think you've read these two books thoroughly, look at their source code.

Moreover, before reading the source code, you will find that they use a lot of third-party Jar packages, 20 or 30, and you figure out those Jar packages one by one.

When it comes to enterprise applications, workflow is bound to be involved. I read the source code of jBPM at that time, and there are articles about the kernel of jBPM on the Internet (Silver Fox). I feel that its core is only two thousand lines, don't be afraid. I used to read the jBPM source blog.

Of course, read the workflow source code, the premise is that you must have an in-depth understanding of its theoretical model, and have written some demo, or done some projects.

What I introduced above is what I have read by myself, and it is also suitable for ordinary people to read.

I have also read some non-Java source code, which feels good and is also recommended to you:

Dojo source code its architecture is elegantly designed, imitating Java's import and extends. But the practical application is a mess. We developed our own framework based on this, but I'm not the main force.

Flex source Flex at the end of 2008 just after the open source, I used it to do a medium-sized project, it should be said to be a domestic technology forerunner. There were no in-depth books and open source projects on the market at that time. I just read Flex's Help documentation and source code to get the project done. Two or three years have passed, and now I think the design of the system is quite elegant.

At this point, I believe you have a deeper understanding of "how to read Java source code". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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