ch07.html

java2高级编程

Button</EM>
, use <EM CLASS="CODE">
stop in java.awt.Button.&lt;init&gt;(java.lang.String)</EM>
. </P>
<P CLASS="Body">
<A NAME="pgfId-1087680"></A>Later releases of <EM CLASS="CODE">
jdb</EM>
 let you choose the desired method as a numbered option.</P>
<P CLASS="Body">
<A NAME="pgfId-1087682"></A><EM CLASS="Bold">
The </EM>
<EM CLASS="C-Code">
cont</EM>
<EM CLASS="Bold">
 Command. </EM>
<A NAME="marker-1087681"></A>To continue the <EM CLASS="CODE">
jdb</EM>
 session, use the <EM CLASS="CODE">
cont</EM>
 command. The next time the program creates a <EM CLASS="CODE">
Button</EM>
 with a <EM CLASS="CODE">
String</EM>
 as the constructor, <EM CLASS="CODE">
jdb</EM>
 stops so that you can examine the output. </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087683"></A>main[1] cont </PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087684"></A>main[1] </PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087685"></A>Breakpoint hit: java.awt.Button.&lt;init&gt; (Button:130)</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087686"></A>If the <EM CLASS="CODE">
Button</EM>
 class had not been recompiled with debug information as described earlier, you would not see the internal fields from the <EM CLASS="CODE">
print</EM>
 command. </P>
<P CLASS="Body">
<A NAME="pgfId-1087689"></A><EM CLASS="Bold">
Clearing Breakpoints. </EM>
<A NAME="marker-1087687"></A><A NAME="marker-1087688"></A>To clear this breakpoint and not stop every time a <EM CLASS="CODE">
Button</EM>
 is created, use the <EM CLASS="CODE">
clear</EM>
 command. This example uses the <EM CLASS="CODE">
clear</EM>
 command with no arguments to display the list of current breakpoints and the <EM CLASS="CODE">
clear</EM>
 command with the <EM CLASS="CODE">
java.awt.Button:130</EM>
 argument to clear the <EM CLASS="CODE">
java.awt.Button:130</EM>
 breakpoint. </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087690"></A>main[1] clear
Current breakpoints set:
SimpleJdbTest:10
java.awt.Button:130
main[1] clear java.awt.Button:130
Breakpoint cleared at java.awt.Button: 130</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087692"></A><EM CLASS="Bold">
Displaying Object Details. </EM>
<A NAME="marker-1087691"></A>To display details about an object, use the <EM CLASS="CODE">
print</EM>
 command to call the object's <EM CLASS="CODE">
toString</EM>
 method, or use the <EM CLASS="CODE">
dump</EM>
 command to display the object's fields and values. </P>
<P CLASS="Body">
<A NAME="pgfId-1087693"></A>This example puts a breakpoint at line 17 and uses the <EM CLASS="CODE">
print</EM>
 and <EM CLASS="CODE">
dump</EM>
 commands to print and dump the first <EM CLASS="CODE">
Button</EM>
 object in the array of <EM CLASS="CODE">
Button</EM>
 objects. The <EM CLASS="CODE">
dump</EM>
 command output has been abbreviated. </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087694"></A>main[1] stop at SimpleJdbTest:17
Breakpoint set at SimpleJdbTest:17
main[1] cont
main[1]
Breakpoint hit: SimpleJdbTest.setup (SimpleJdbTest:17)

main[1] print b[0]
b[0] = java.awt.Button[button1,0,0,0x0,invalid,label=press]
main[1] dump b[0]
b[0] = (java.awt.Button)0x163 {
private int componentSerializedDataVersion = 2
boolean isPacked = false
private java.beans.PropertyChangeSupport changeSupport = null
long eventMask = 4096
transient java.awt.event.InputMethodListener 
			inputMethodListener = null
....
java.lang.String actionCommand = null
java.lang.String label = press
}</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087696"></A><EM CLASS="Bold">
Ending the Session. </EM>
<A NAME="marker-1087695"></A>That finishes the simple <EM CLASS="CODE">
jdb</EM>
 examples. To terminate the <EM CLASS="CODE">
jdb</EM>
 session, use the <EM CLASS="CODE">
quit</EM>
 command: </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087697"></A>0xee2f9820:class(SimpleJdbTest)
&gt; quit</PRE>
</DIV>
</DIV>
<DIV>
<H5 CLASS="B">
<A NAME="pgfId-1087699"></A><A NAME="58498"></A>Remote Debugging</H5>
<P CLASS="Body">
<A NAME="pgfId-1087702"></A><A NAME="marker-1087700"></A><A NAME="marker-1087701"></A>The <EM CLASS="CODE">
jdb</EM>
 tool is an external process debugger, which means it debugs the program by sending messages to and from a helper inside the Java virtual machine. This makes it easy to debug a running program and helps you debug a program that interacts with the end user. A remote debug session from the command line does not interfere with the normal operation of the application. </P>
<P CLASS="Body">
<A NAME="pgfId-1087703"></A><EM CLASS="Bold">
Starting the Session. </EM>
Before the Java 2 release, the only thing required to enable remote debugging was to start the program with the <EM CLASS="CODE">
-debug</EM>
 flag as the first argument, and if the application uses native libraries, make the library name end in <EM CLASS="CODE">
_g</EM>
. For example, you would need to copy <EM CLASS="CODE">
nativelib.dll</EM>
 to <EM CLASS="CODE">
nativelib_g.dll</EM>
 to debug with that library. </P>
<P CLASS="Body">
<A NAME="pgfId-1087704"></A>In Java 2, choices are a little more complicated. You need to tell the Java virtual machine where the <EM CLASS="CODE">
tools.jar</EM>
 file is with the <EM CLASS="CODE">
CLASSPATH</EM>
 variable. The <EM CLASS="CODE">
tools.jar</EM>
 file contains noncore class files to support tools and utilities in the SDK. It is normally found in the <EM CLASS="CODE">
lib</EM>
 directory of the Java platform installation. </P>
<P CLASS="Body">
<A NAME="pgfId-1087706"></A>You also need to disable the <A NAME="marker-1087705"></A>Just In Time (JIT) compiler if one exists. The JIT compiler is disabled by setting the <EM CLASS="CODE">
java.compiler</EM>
 property to <EM CLASS="CODE">
NONE</EM>
 or to an empty string. Finally, as the <EM CLASS="CODE">
-classpath</EM>
 option overrides any previously set user classpath, you also need to add the <EM CLASS="CODE">
CLASSPATH</EM>
 needed by your application. </P>
<P CLASS="Body">
<A NAME="pgfId-1087707"></A>Putting all of this together, here is the command line needed to start a program in remote debug mode. Put this all on one line and include all the classes you need on the command line. </P>
<DIV>
<H6 CLASS="D">
<A NAME="pgfId-1087708"></A><EM CLASS="Bold">
Windows:</EM>
</H6>
<PRE CLASS="CODE"><A NAME="pgfId-1087709"></A>$ java -debug -classpath C:&#92;java&#92;lib&#92;tools.jar;. 
-Djava.compiler=NONE SimpleJdbTest Agent password=4gk5hm</PRE>
</DIV>
<DIV>
<H6 CLASS="D">
<A NAME="pgfId-1087710"></A><EM CLASS="Bold">
Unix:</EM>
</H6>
<PRE CLASS="CODE"><A NAME="pgfId-1087711"></A>$ java -debug -classpath /usr/java/lib/tools.jar:. 
-Djava.compiler=NONE SimpleJdbTest Agent password=5ufhic</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087714"></A>The output is the <A NAME="marker-1087712"></A><A NAME="marker-1087713"></A>agent password (in this case, <EM CLASS="CODE">
4gk5hm</EM>
) if the program was successfully started. The agent password is supplied when starting <EM CLASS="CODE">
jdb</EM>
 so <EM CLASS="CODE">
jdb</EM>
 can find the corresponding application started in debug mode on that machine. </P>
<P CLASS="Body">
<A NAME="pgfId-1087716"></A><A NAME="marker-1087715"></A>To start <EM CLASS="CODE">
jdb</EM>
 in remote debug mode, supply a host name, which can be either the machine where the remote program was started or <EM CLASS="CODE">
localhost</EM>
 if you are debugging on the same machine as the remote program, and the agent password. </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087717"></A>jdb -host localhost -password 4gk5hm</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087719"></A><EM CLASS="Bold">
Listing Threads. </EM>
<A NAME="marker-1087718"></A>Once inside the <EM CLASS="CODE">
jdb</EM>
 session, you can list the currently active threads with the <EM CLASS="CODE">
threads</EM>
 command and use the <EM CLASS="CODE">
thread &lt;threadnumber&gt;</EM>
 command (for example, <EM CLASS="CODE">
thread 7)</EM>
 to select the thread to analyze. Once the thread is selected, use the <EM CLASS="CODE">
where</EM>
 command to see which methods have been called for this thread. </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087720"></A>$ jdb -host arsenal -password 5ufhic</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087721"></A>Initializing jdb...</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087722"></A>&gt; threads</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087723"></A>Group system:</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087724"></A>1. (java.lang.Thread)0x9        Signal dispatcher 
                               cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087725"></A>2. (java.lang.ref.Reference     0xb Reference Handler</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087726"></A>      $ReferenceHandler)        cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087727"></A>3. (java.lang.ref.              Finalizer</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087728"></A>      Finalizer                cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087729"></A>      $FinalizerThread)0xd</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087730"></A>       </PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087731"></A>4. (java.lang.Thread)0xe       Debugger agent</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087732"></A>                               running</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087733"></A>5. (sun.tools.agent.           Breakpoint handler</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087734"></A>      Handler)0x10             cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087735"></A>6. (sun.tools.agent.           Step handler</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087736"></A>      StepHandler)0x12         cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087737"></A>Group main:</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087738"></A>7. (java.awt.                  AWT-EventQueue-0</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087739"></A>       EventDispatchThread)    cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087740"></A>       0x19</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087741"></A>8. (sun.awt.                    PostEventQueue-0</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087742"></A>      PostEventQueue)0x1b       cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087743"></A>9. (java.lang.Thread)0x1c       AWT-Motif</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087744"></A>                                running</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087745"></A>10. (java.lang.Thread)0x1d      TimerQueue</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087746"></A>                                cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087747"></A>11. (sun.awt.                   Screen Updater</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087748"></A>       ScreenUpdater)0x1f       cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087749"></A>12. (java.lang.Thread)0x20      Thread-0</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087750"></A>                                cond. waiting</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087751"></A>&gt; thread 7</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087752"></A>AWT-EventQueue-0[1] where</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087753"></A>  [1] java.lang.Object.wait (native method)</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087754"></A>  [2] java.lang.Object.wait (Object:424)</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087755"></A>  [3] java.awt.EventQueue.getNextEvent (EventQueue:179)</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087756"></A>  [4] java.awt.EventDispatchThread.run (EventDispatchThread:67)</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087758"></A><EM CLASS="Bold">
Listing Source. </EM>
<A NAME="marker-1087757"></A>To list the source, the thread needs to be suspended using the <EM CLASS="CODE">
suspend</EM>
 command. To let this thread continue, use the <EM CLASS="CODE">
resume</EM>
 command. The example uses <EM CLASS="CODE">
resume 7.</EM>
 </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087759"></A>AWT-EventQueue-0[1] suspend 7</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087760"></A>AWT-EventQueue-0[1] list </PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087761"></A>Current method is native </PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087762"></A>AWT-EventQueue-0[1] where</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087763"></A>   [1] java.lang.Object.wait (native method)</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087764"></A>   [2] java.lang.Object.wait (Object:424)</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087765"></A>   [3] java.awt.EventQueue.getNextEvent   (EventQueue:179)</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087766"></A>   [4] java.awt.EventDispatchThread.run (EventDispatchThread:67)</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087767"></A>AWT-EventQueue-0[1] resume 7</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087769"></A><EM CLASS="Bold">
Ending the Session. </EM>
<A NAME="marker-1087768"></A>When you finish debugging this program remotely, clear any remaining breakpoints before quitting the debug session. To get a list of remaining breakpoints use the <EM CLASS="CODE">
clear</EM>
 command, and to remove them, enter <EM CLASS="CODE">
clear class:linenumber</EM>
 as follows: </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087770"></A>main[1] clear
Current breakpoints set:
SimpleJdbTest:10

main[1] clear SimpleJdbTest:10
main[1] quit</PRE>
</DIV>
</DIV>
<DIV>
<H5 CLASS="B">