1、代码

2、编译代码

3、调试

3.1 jdb

3.2 stop

3.3 list

3.4 run

3.5 list

3.6 step

3.7 print dump eval

3.8 set

3.9 locals

3.10 next

3.11 cont

3.12 n 命令

3.13 help

3.14 !!

3.15 version

4、spring boot调试

4.1 代码

4.2 启动脚本

4.3 连接debug端口

4.3.1 连接

4.3.2 打断点

4.3.3 访问接口

4.3.4 调试

1、代码

/**
 * @ClassName Num
 * @Description:
 * @Author ybwei
 * @Date 2020/10/30
 * @Version V1.0
 **/
public class Num {
    public static int add(int a,int b){
        return a+b;
    }
    public static void main(String[] args) {
        int a=3;
        int b=5;
        int c=a+b;
        System.out.println(c);
    }
}

2、编译代码

>javac -g Num.java

-g

生成所有的调试信息，包括局部变量。缺省情况下，只生成行号和源文件信息。

通过这个参数，可以在生成的class文件中，添加具体的 line,source,vars 信息，具体的作用体现在：

因为调试的时候需要符号信息，所以一定需要这个参数
在抛出Exception的时候，可以知道具体的错误位置，而非Unknown Source。

添加了这个参数后，不可避免的class文件会变大一点，但是为了以后的维护，还是非常值得的。

3、调试

3.1 jdb

Num.class添加到JDB进行调试。

[root@iZ2ze8o82mhgjvdsmrwz8bZ test]# jdb Num
Initializing jdb ...

3.2 stop

加载成功后，我们通常会在 main函数的位置加上断点

> stop in Num.main
Deferring breakpoint Num.main.
It will be set after the class is loaded.

3.3 list

查看被成功加入的断点

> clear
Breakpoints set:
    breakpoint Num.main

3.4 run

运行程序，程序暂停到main函数的第一行

> run
run Num
Set uncaught java.lang.Throwable
Set deferred uncaught java.lang.Throwable
> 
VM Started: Set deferred breakpoint Num.main
Breakpoint hit: "thread=main", Num.main(), line=15 bci=0
15            int a=3;
main[1]

3.5 list

查看源代码，=>当前正在执行的行

main[1] list
11            return a+b;
12        }
13    
14        public static void main(String[] args) {
15 =>         int a=3;
16            int b=5;
17            int c=a+b;
18            System.out.println(c);
19        }
20    }

3.6 step

下一步

main[1] step
Step completed: "thread=main", Num.main(), line=16 bci=2
16            int b=5;

3.7 print dump eval

main[1] main[1] print a
 a = 3
main[1] dump a
 a = 3
main[1] eval a
 a = 3

3.8 set

修改变量

main[1] set a=1
 a=1 = 1
main[1] print a
 a = 1

3.9 locals

显示当前堆栈帧中的所有本地变量

main[1] locals
Method arguments:
args = instance of java.lang.String[0] (id=385)
Local variables:
a = 1

3.10 next

下一步

main[1] next
> 
Step completed: "thread=main", Num.main(), line=17 bci=4
17            int c=a+b;

next和step的区别

在执行有方法调用的语句时，next会把方法执行完，step会进入方法体。所以在调试时，单步执行我们要优先使用next，这样效率比较高。

3.11 cont

从当前位置直接执行到程序结束（或者下一个断点或信号）

main[1] cont
6
> 
The application exited
[root@iZ2ze8o82mhgjvdsmrwz8bZ test]#

3.12 n 命令

将某个命令重复执行n次

[root@iZ2ze8o82mhgjvdsmrwz8bZ test]# jdb Num
Initializing jdb ...
> stop in Num.main
Deferring breakpoint Num.main.
It will be set after the class is loaded.
> run
run Num
Set uncaught java.lang.Throwable
Set deferred uncaught java.lang.Throwable
> 
VM Started: Set deferred breakpoint Num.main
Breakpoint hit: "thread=main", Num.main(), line=15 bci=0
15            int a=3;
main[1] 2 step
Step completed: "thread=main", Num.main(), line=16 bci=2
16            int b=5;
main[1] main[1] 
Step completed: "thread=main", Num.main(), line=17 bci=4
17            int c=a+b;

3.13 help

main[1] main[1] help 
** command list **
connectors                -- list available connectors and transports in this VM
run [class [args]]        -- start execution of application's main class
threads [threadgroup]     -- list threads
thread <thread id>        -- set default thread
suspend [thread id(s)]    -- suspend threads (default: all)
resume [thread id(s)]     -- resume threads (default: all)
where [<thread id> | all] -- dump a thread's stack
wherei [<thread id> | all]-- dump a thread's stack, with pc info
up [n frames]             -- move up a thread's stack
down [n frames]           -- move down a thread's stack
kill <thread id> <expr>   -- kill a thread with the given exception object
interrupt <thread id>     -- interrupt a thread
print <expr>              -- print value of expression
dump <expr>               -- print all object information
eval <expr>               -- evaluate expression (same as print)
set <lvalue> = <expr>     -- assign new value to field/variable/array element
locals                    -- print all local variables in current stack frame
classes                   -- list currently known classes
class <class id>          -- show details of named class
methods <class id>        -- list a class's methods
fields <class id>         -- list a class's fields
threadgroups              -- list threadgroups
threadgroup <name>        -- set current threadgroup
stop in <class id>.<method>[(argument_type,...)]
                          -- set a breakpoint in a method
stop at <class id>:<line> -- set a breakpoint at a line
clear <class id>.<method>[(argument_type,...)]
                          -- clear a breakpoint in a method
clear <class id>:<line>   -- clear a breakpoint at a line
clear                     -- list breakpoints
catch [uncaught|caught|all] <class id>|<class pattern>
                          -- break when specified exception occurs
ignore [uncaught|caught|all] <class id>|<class pattern>
                          -- cancel 'catch' for the specified exception
watch [access|all] <class id>.<field name>
                          -- watch access/modifications to a field
unwatch [access|all] <class id>.<field name>
                          -- discontinue watching access/modifications to a field
trace [go] methods [thread]
                          -- trace method entries and exits.
                          -- All threads are suspended unless 'go' is specified
trace [go] method exit | exits [thread]
                          -- trace the current method's exit, or all methods' exits
                          -- All threads are suspended unless 'go' is specified
untrace [methods]         -- stop tracing method entrys and/or exits
step                      -- execute current line
step up                   -- execute until the current method returns to its caller
stepi                     -- execute current instruction
next                      -- step one line (step OVER calls)
cont                      -- continue execution from breakpoint
list [line number|method] -- print source code
use (or sourcepath) [source file path]
                          -- display or change the source path
exclude [<class pattern>, ... | "none"]
                          -- do not report step or method events for specified classes
classpath                 -- print classpath info from target VM
monitor <command>         -- execute command each time the program stops
monitor                   -- list monitors
unmonitor <monitor#>      -- delete a monitor
read <filename>           -- read and execute a command file
lock <expr>               -- print lock info for an object
threadlocks [thread id]   -- print lock info for a thread
pop                       -- pop the stack through and including the current frame
reenter                   -- same as pop, but current frame is reentered
redefine <class id> <class file name>
                          -- redefine the code for a class
disablegc <expr>          -- prevent garbage collection of an object
enablegc <expr>           -- permit garbage collection of an object
!!                        -- repeat last command
<n> <command>             -- repeat command n times
# <command>               -- discard (no-op)
help (or ?)               -- list commands
version                   -- print version information
exit (or quit)            -- exit debugger
<class id>: a full class name with package qualifiers
<class pattern>: a class name with a leading or trailing wildcard ('*')
<thread id>: thread number as reported in the 'threads' command
<expr>: a Java(TM) Programming Language expression.
Most common syntax is supported.
Startup commands can be placed in either "jdb.ini" or ".jdbrc"
in user.home or user.dir

3.14 !!

重复执行上一命令，如下重新执行step

main[1] step
> 
Step completed: "thread=main", Num.main(), line=18 bci=8
18            System.out.println(c);
main[1] !!
step
8
> 
Step completed: "thread=main", Num.main(), line=19 bci=15
19        }

3.15 version

jdb版本号