Suppose you are working on a project and want to include a library jar file which has specific java class. But at the same time you don't have much idea about which jar file to include and you are given with a lot of jar files to choose from. How would you figure out which jar file is the most suitable one.
Well here comes Jarscan to rescue. Jarscan is an executable jar file which scans the jar/zip file and lists jar files which contains the desired class.
Well here comes Jarscan to rescue. Jarscan is an executable jar file which scans the jar/zip file and lists jar files which contains the desired class.
- Java 1.4 or higher version should be installed in your system. If your system doesn't have it then you can download it from here.
- Jarscan which can be downloaded from here.
java -jar jarscan.jar -help #This provides help, how to use jarscan. java -jar jarscan.jar #This works as the command above. #The following command looks for Activity class root from current directory. java -jar jarscan.jar -dir . -class ActivityYou can even search classes through database of libraries online here. If you want more information about Jarscan you can find it here.
You can try the online services here.
- www.findjar.com
- www.jarfinder.com
- www.jarhoo.com
- www.docjar.com
- javacio.us
- merobase.com
- jar-explorer
Java class file decompilation
What if you are interested to know more about the class methods, variable, etc. and the only thing that you have is the class file. Don't worry, there is a way to know about these methods, variables etc. even without source file. Javap can help you parsing the class file and providing the information about the desired class. Javap executable comes with java package. Most of the people either aren't aware of it or don't use it because they rely more on IDE(e.g Eclpse)/build system. Here we are going to use the javap command option for the following class.
package com.rakesh.simplewidget;
import android.appwidget.AppWidgetManager;
import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.util.Log;
import android.widget.RemoteViews;
import android.widget.Toast;
public class ConnectivityReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
NetworkInfo info = (NetworkInfo)intent.getExtras().get(ConnectivityManager.EXTRA_NETWORK_INFO);
if(info.getType() == ConnectivityManager.TYPE_MOBILE){
RemoteViews remoteViews = new RemoteViews(context.getPackageName(),
R.layout.widget_layout);
if(info.isConnectedOrConnecting()){
Toast.makeText(context, "Data packet enabled", Toast.LENGTH_SHORT).show();
Log.d("RK","Mobile data is enabled");
remoteViews.setTextColor(R.id.BtEnableDisable, Color.GREEN);
remoteViews.setTextViewText(R.id.BtEnableDisable, "Enabled");
}else{
Toast.makeText(context, "Data packet disabled", Toast.LENGTH_SHORT).show();
Log.e("RK","Mobile data is disconnected");
remoteViews.setTextColor(R.id.BtEnableDisable, Color.BLACK);
remoteViews.setTextViewText(R.id.BtEnableDisable,"Disabled");
}
ComponentName thiswidget = new ComponentName(context, SimpleWidgetAppWidgetProvider.class);
AppWidgetManager manager = AppWidgetManager.getInstance(context);
manager.updateAppWidget(thiswidget, remoteViews);
}
}
}
Compile the java file and then run the commands below.
# Sanity check. If you don't get below message after executing javap command
# then include the java installation folder path in system path.
$javap
No classes were specified on the command line. Try -help.
$javap -help #This command lists all the options available with javap
Usage: javap <options> <classes>...
where options include:
-c Disassemble the code
-classpath <pathlist> Specify where to find user class files
-extdirs <dirs> Override location of installed extensions
-help Print this usage message
-J<flag> Pass <flag> directly to the runtime system
-l Print line number and local variable tables
-public Show only public classes and members
-protected Show protected/public classes and members
-package Show package/protected/public classes
and members (default)
-private Show all classes and members
-s Print internal type signatures
-bootclasspath <pathlist> Override location of class files loaded
by the bootstrap class loader
-verbose Print stack size, number of locals and args for methods
If verifying, print reasons for failure
#This command decompile the ConnectivityReceiver class file
$javap -c ConnectivityReceiver
Compiled from "ConnectivityReceiver.java"
public class com.rakesh.simplewidget.ConnectivityReceiver extends android.content.BroadcastReceiver{
public com.rakesh.simplewidget.ConnectivityReceiver();
Code:
0: aload_0
1: invokespecial #8; //Method android/content/BroadcastReceiver."<init>":()V
4: return
public void onReceive(android.content.Context, android.content.Intent);
Code:
0: aload_2
1: invokevirtual #16; //Method android/content/Intent.getExtras:()Landroid/os/Bundle;
4: ldc #22; //String networkInfo
6: invokevirtual #24; //Method android/os/Bundle.get:(Ljava/lang/String;)Ljava/lang/Object;
9: checkcast #30; //class android/net/NetworkInfo
12: astore_3
13: aload_3
14: invokevirtual #32; //Method android/net/NetworkInfo.getType:()I
17: ifne 144
20: new #36; //class android/widget/RemoteViews
23: dup
24: aload_1
25: invokevirtual #38; //Method android/content/Context.getPackageName:()Ljava/lang/String;
28: ldc #44; //int 2130903041
30: invokespecial #45; //Method android/widget/RemoteViews."<init>":(Ljava/lang/String;I)V
33: astore 4
35: aload_3
36: invokevirtual #48; //Method android/net/NetworkInfo.isConnectedOrConnecting:()Z
39: ifeq 81
42: aload_1
43: ldc #52; //String Data packet enabled
45: iconst_0
46: invokestatic #54; //Method android/widget/Toast.makeText:(Landroid/content/Context;Ljava/lang/CharSequence;I)Landroid/widget/Toast;
49: invokevirtual #60; //Method android/widget/Toast.show:()V
52: ldc #63; //String RK
54: ldc #65; //String Mobile data is enabled
56: invokestatic #67; //Method android/util/Log.d:(Ljava/lang/String;Ljava/lang/String;)I
59: pop
60: aload 4
62: ldc #73; //int 2131099649
64: ldc #74; //int -16711936
66: invokevirtual #75; //Method android/widget/RemoteViews.setTextColor:(II)V
69: aload 4
71: ldc #73; //int 2131099649
73: ldc #79; //String Enabled
75: invokevirtual #81; //Method android/widget/RemoteViews.setTextViewText:(ILjava/lang/CharSequence;)V
78: goto 117
81: aload_1
82: ldc #85; //String Data packet disabled
84: iconst_0
85: invokestatic #54; //Method android/widget/Toast.makeText:(Landroid/content/Context;Ljava/lang/CharSequence;I)Landroid/widget/Toast;
88: invokevirtual #60; //Method android/widget/Toast.show:()V
91: ldc #63; //String RK
93: ldc #87; //String Mobile data is disconnected
95: invokestatic #89; //Method android/util/Log.e:(Ljava/lang/String;Ljava/lang/String;)I
98: pop
99: aload 4
101: ldc #73; //int 2131099649
103: ldc #92; //int -16777216
105: invokevirtual #75; //Method android/widget/RemoteViews.setTextColor:(II)V
108: aload 4
110: ldc #73; //int 2131099649
112: ldc #93; //String Disabled
114: invokevirtual #81; //Method android/widget/RemoteViews.setTextViewText:(ILjava/lang/CharSequence;)V
117: new #95; //class android/content/ComponentName
120: dup
121: aload_1
122: ldc #97; //class com/rakesh/simplewidget/SimpleWidgetAppWidgetProvider
124: invokespecial #99; //Method android/content/ComponentName."<init>":(Landroid/content/Context;Ljava/lang/Class;)V
127: astore 5
129: aload_1
130: invokestatic #102; //Method android/appwidget/AppWidgetManager.getInstance:(Landroid/content/Context;)Landroid/appwidget/AppWidgetManager;
133: astore 6
135: aload 6
137: aload 5
139: aload 4
141: invokevirtual #108; //Method android/appwidget/AppWidgetManager.updateAppWidget:(Landroid/content/ComponentName;Landroid/widget/RemoteViews;)V
144: return
}
#This command lists the line number and local variables
$ javap -l ConnectivityReceiver
Compiled from "ConnectivityReceiver.java"
public class com.rakesh.simplewidget.ConnectivityReceiver extends android.content.BroadcastReceiver{
public com.rakesh.simplewidget.ConnectivityReceiver();
LineNumberTable:
line 15: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/rakesh/simplewidget/ConnectivityReceiver;
public void onReceive(android.content.Context, android.content.Intent);
LineNumberTable:
line 19: 0
line 21: 13
line 23: 20
line 24: 28
line 23: 30
line 26: 35
line 27: 42
line 28: 52
line 29: 60
line 30: 69
line 32: 81
line 33: 91
line 34: 99
line 35: 108
line 38: 117
line 39: 129
line 40: 135
line 43: 144
LocalVariableTable:
Start Length Slot Name Signature
0 145 0 this Lcom/rakesh/simplewidget/ConnectivityReceiver;
0 145 1 context Landroid/content/Context;
0 145 2 intent Landroid/content/Intent;
13 132 3 info Landroid/net/NetworkInfo;
35 109 4 remoteViews Landroid/widget/RemoteViews;
129 15 5 thiswidget Landroid/content/ComponentName;
135 9 6 manager Landroid/appwidget/AppWidgetManager;
}
#This command prints internal type signatures
$ javap -s ConnectivityReceiver
Compiled from "ConnectivityReceiver.java"
public class com.rakesh.simplewidget.ConnectivityReceiver extends android.content.BroadcastReceiver{
public com.rakesh.simplewidget.ConnectivityReceiver();
Signature: ()V
public void onReceive(android.content.Context, android.content.Intent);
Signature: (Landroid/content/Context;Landroid/content/Intent;)V
}
#This command shows package/protected/public classes and members (default)
$ javap -package ConnectivityReceiver
Compiled from "ConnectivityReceiver.java"
public class com.rakesh.simplewidget.ConnectivityReceiver extends android.content.BroadcastReceiver{
public com.rakesh.simplewidget.ConnectivityReceiver();
public void onReceive(android.content.Context, android.content.Intent);
}
#Similar way you can also use -public, -protected -private etc. options
Related topic:
Android/java source code browsing
Your valuable comments are always welcomed. It will help to improve my post and understanding.
"By three methods we may learn wisdom: First, by reflection, which is noblest; Second, by imitation, which is easiest; and third by experience, which is the bitterest."
By : Confucius
