1jdb(1) Basic Tools jdb(1)
2
6 jdb - Finds and fixes bugs in Java platform programs.
7
9 jdb [options] [classname] [arguments]
10 options
13 Command-line options. See Options.
14 classname
16 Name of the main class to debug.
17 arguments
19 Arguments passed to the main() method of the class.
20
22 The Java Debugger (JDB) is a simple command-line debugger for Java
23 classes. The jdb command and its options call the JDB. The jdb command
24 demonstrates the Java Platform Debugger Architecture (JDBA) and
25 provides inspection and debugging of a local or remote Java Virtual
26 Machine (JVM). See Java Platform Debugger Architecture (JDBA) at
27 http://docs.oracle.com/javase/8/docs/technotes/guides/jpda/index.html
28 START A JDB SESSION
30 There are many ways to start a JDB session. The most frequently used
31 way is to have JDB launch a new JVM with the main class of the
32 application to be debugged. Do this by substituting the jdb command for
33 the java command in the command line. For example, if your
34 application's main class is MyClass, then use the following command to
35 debug it under JDB:
36 jdb MyClass
38 When started this way, the jdb command calls a second JVM with the
40 specified parameters, loads the specified class, and stops the JVM
41 before executing that class's first instruction.
42 Another way to use the jdb command is by attaching it to a JVM that is
44 already running. Syntax for starting a JVM to which the jdb command
45 attaches when the JVM is running is as follows. This loads in-process
46 debugging libraries and specifies the kind of connection to be made.
47 java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n MyClass
49 You can then attach the jdb command to the JVM with the following
51 command:
52 jdb -attach 8000
54 The MyClass argument is not specified in the jdb command line in this
56 case because the jdb command is connecting to an existing JVM instead
57 of launching a new JVM.
58 There are many other ways to connect the debugger to a JVM, and all of
60 them are supported by the jdb command. The Java Platform Debugger
61 Architecture has additional documentation on these connection options.
62 BASIC JDB COMMANDS
64 The following is a list of the basic jdb commands. The JDB supports
65 other commands that you can list with the -help option.
66 help or ?
68 The help or ? commands display the list of recognized commands
69 with a brief description.
70 run After you start JDB and set breakpoints, you can use the run
72 command to execute the debugged application. The run command is
73 available only when the jdb command starts the debugged
74 application as opposed to attaching to an existing JVM.
75 cont Continues execution of the debugged application after a
77 breakpoint, exception, or step.
78 print Displays Java objects and primitive values. For variables or
80 fields of primitive types, the actual value is printed. For
81 objects, a short description is printed. See the dump command to
82 find out how to get more information about an object.
83 Note: To display local variables, the containing class must have
85 been compiled with the javac -g option.
86 The print command supports many simple Java expressions
88 including those with method invocations, for example:
89 print MyClass.myStaticField
91 print myObj.myInstanceField
92 print i + j + k (i, j, k are primities and either fields or local variables)
93 print myObj.myMethod() (if myMethod returns a non-null)
94 print new java.lang.String("Hello").length()
95 dump For primitive values, the dump command is identical to the print
99 command. For objects, the dump command prints the current value
100 of each field defined in the object. Static and instance fields
101 are included. The dump command supports the same set of
102 expressions as the print command.
103 threads
105 List the threads that are currently running. For each thread,
106 its name and current status are printed and an index that can be
107 used in other commands. In this example, the thread index is 4,
108 the thread is an instance of java.lang.Thread, the thread name
109 is main, and it is currently running.
110 4. (java.lang.Thread)0x1 main running
112 thread Select a thread to be the current thread. Many jdb commands are
116 based on the setting of the current thread. The thread is
117 specified with the thread index described in the threads
118 command.
119 where The where command with no arguments dumps the stack of the
121 current thread. The whereall command dumps the stack of all
122 threads in the current thread group. The wherethreadindex
123 command dumps the stack of the specified thread.
124 If the current thread is suspended either through an event such
126 as a breakpoint or through the suspend command, then local
127 variables and fields can be displayed with the print and dump
128 commands. The up and down commands select which stack frame is
129 the current stack frame.
130 BREAKPOINTS
132 Breakpoints can be set in JDB at line numbers or at the first
133 instruction of a method, for example:
134 · The command stop at MyClass:22 sets a breakpoint at the first
136 instruction for line 22 of the source file containing MyClass.
137 · The command stop in java.lang.String.length sets a breakpoint at the
139 beginning of the method java.lang.String.length.
140 · The command stop in MyClass.<clinit> uses <clinit> to identify the
142 static initialization code for MyClass.
143 When a method is overloaded, you must also specify its argument types
145 so that the proper method can be selected for a breakpoint. For
146 example, MyClass.myMethod(int,java.lang.String) or MyClass.myMethod().
147 The clear command removes breakpoints using the following syntax: clear
149 MyClass:45. Using the clear or stop command with no argument displays a
150 list of all breakpoints currently set. The cont command continues
151 execution.
152 STEPPING
154 The step command advances execution to the next line whether it is in
155 the current stack frame or a called method. The next command advances
156 execution to the next line in the current stack frame.
157 EXCEPTIONS
159 When an exception occurs for which there is not a catch statement
160 anywhere in the throwing thread's call stack, the JVM typically prints
161 an exception trace and exits. When running under JDB, however, control
162 returns to JDB at the offending throw. You can then use the jdb command
163 to diagnose the cause of the exception.
164 Use the catch command to cause the debugged application to stop at
166 other thrown exceptions, for example: catch
167 java.io.FileNotFoundException or catchmypackage.BigTroubleException.
168 Any exception that is an instance of the specified class or subclass
169 stops the application at the point where it is thrown.
170 The ignore command negates the effect of an earlier catch command. The
172 ignore command does not cause the debugged JVM to ignore specific
173 exceptions, but only to ignore the debugger.
174
176 When you use the jdb command instead of the java command on the command
177 line, the jdb command accepts many of the same options as the java
178 command, including -D, -classpath, and -X options. The following list
179 contains additional options that are accepted by the jdb command.
180 Other options are supported to provide alternate mechanisms for
182 connecting the debugger to the JVM it is to debug. For additional
183 documentation about these connection alternatives, see Java Platform
184 Debugger Architecture (JPDA) at
185 http://docs.oracle.com/javase/8/docs/technotes/guides/jpda/index.html
186 -help
188 Displays a help message.
189 -sourcepath dir1:dir2: . . .
191 Uses the specified path to search for source files in the
192 specified path. If this option is not specified, then use the
193 default path of dot (.).
194 -attach address
196 Attaches the debugger to a running JVM with the default
197 connection mechanism.
198 -listen address
200 Waits for a running JVM to connect to the specified address with
201 a standard connector.
202 -launch
204 Starts the debugged application immediately upon startup of JDB.
205 The -launch option removes the need for the run command. The
206 debugged application is launched and then stopped just before
207 the initial application class is loaded. At that point, you can
208 set any necessary breakpoints and use the cont command to
209 continue execution.
210 -listconnectors
212 List the connectors available in this JVM.
213 -connect connector-name:name1=value1
215 Connects to the target JVM with the named connector and listed
216 argument values.
217 -dbgtrace [flags]
219 Prints information for debugging the jdb command.
220 -tclient
222 Runs the application in the Java HotSpot VM client.
223 -tserver
225 Runs the application in the Java HotSpot VM server.
226 -Joption
228 Passes option to the JVM, where option is one of the options
229 described on the reference page for the Java application
230 launcher. For example, -J-Xms48m sets the startup memory to 48
231 MB. See java(1).
232
234 -v -verbose[:class|gc|jni]
235 Turns on verbose mode.
236 -Dname=value
238 Sets a system property.
239 -classpath dir
241 Lists directories separated by colons in which to look for
242 classes.
243 -Xoption
245 Nonstandard target JVM option.
246
248 · javac(1)
249 · java(1)
251 · javap(1)
253JDK 8 21 November 2013 jdb(1)