Java程序调优---去掉 java 项目中 多余的jar包 方法

开发工具Eclipse 3.x


插件一：ClassPath Helper
插件地址：http://classpathhelper.sourceforge.net/

Downloading ClassPath Helper

For starters, you need to download the Classpath Helper eclipse plugins. The files are packaged seperately as binaries and source code plugins. The source code plugins are not required for execution.

The latest version of Classpath Helper can be downloaded from source forge http://classpathhelper.sourceforge.net/downloads.html

Once you download the eclipse distribution zip file, you need to unzip it in your eclipse directory (it will automatically unpack itself in the appropriate subdirectory (i.e. plugins). From there (re)start eclipse. You can verify if the classpath helper plugins are properly installed by selecting Help->About Eclipse SDK, select the "Plug-in Details" button.

Configuring Eclipse

Eclipse by default starts its VM with a very small heap and stack. This leads to some mysterous stack overflows from within Eclipse when plugins are performing long running jobs. This is a well documented bug within Eclipse that affects other plugins. The work around is to increase the stack size upon eclipse startup.

  eclipse.exe -Xms64m 

Opening Classpath Helper Views

The Classpath Helper Views can be opened in any perspective with the following steps.

First, from the Menu select Window->Show View->Other...

Second, under the Classpath Helper category, select the Classpath Helper View, Location By Location View, or Packages View

The Classpath Helper View

The basic layout of this view should be a straight forward translation of the classpath. The classpath is based upon the currently selected model (which initially is taken from the currently selected Java Project from you Package Explorer view).

Familar icons are used for Jar files and class folders. The order is represented top to bottom. The various decorations on these elements will be explained later.

This can be expanded to show the classes and interfaces within each jar or folder.

Unresolved Classes

The highlighted region shows a jar and class file decorated with a . This indicates that a reference to a class cannot be resolved (found) on the current classpath. In this example, a class called anunresolvedjar.ClassMissingFromJar cannot be found. At runtime this would lead to either a java.lang.ClassNotFoundException or a java.lang.NoClassDefFoundError. In either case, the class anunresolvedjar.ClassWithMissingDependency cannot be loaded.

Blocked (Obscured) Classes

The first highlighted region (next to the ) shows jar and class file decorated with a . This indicates a class is 'blocked' or 'obscured' on the classpath. This means that the class/interface located at this location will never be loaded. Instead it is loaded from another location. In this instance, we can see that the class ajar.DependsOnFilesFromFolder will actually be loaded from C:\Development\Sample\demoarea\ajar.jar.

In the second highlighted region (next to the ) we can see the class ajar.DependsOnFilesFromFolder. Although not a critical problem with the classpath, it could be confusing if the jar C:\Development\Sample\demoarea\ablockedjar.jar is updated with a new instance of ajar.DependsOnFilesFromFolder as the newer class will never get loaded into the JVM.

Blocked (Obscured) Classes with different versions

The first highlighted region (next to the  shows a folder and class file with a . This indicates a class is 'blocked' or 'obscured' on the classpath. This is essentially the same as a yellow rectangle with one addition. The red color is also an indication that the version of the class at this location (C:\Development\Sample\demoarea in this example) is different from the version that will actually be loaded (from C:\Development\Sample\build in this example). As with a yellow rectangle, the folder shown below the blocked class is the location where the class will actually get loaded from.

As with the previous example, the second highlight  is showing the folder where the actual class will get loaded from. Of course blocking locations will always be above (appear earlier) in the classpath.

Unreferenced Classes

Classes decorated with the  image indicates a class that is not referenced by any other class. In the above image afolder.AClassWithDependencies is not referenced by any other class. Keep in mind that this information is based solely on references maintained within the classfile itself. There are several notable cases where class files are referenced but this will not be indicated including:

• In cases where Class.forName() is used to load a classes, which is common in many frameworks including struts, WAR web.xml files, EJB descriptors, etc.
• Interface constants (static final constants) are compiled inline. This means that although there's a compile time dependency on the constants at runtime there is no reference to the declaring interface/class.

 

What a Class or Interface Depends On

In addition to showing issues or problems with the classpath, Classpath Helper also can be used to show what classes/interfaces a particular class depends on. The highlighted region shows that the class ajar.DependsOnFilesFromFolder depends on

• afolder.AClassWithNoDependencies loaded from C:\Development\Sample\demoarea
• blocked.BlocksALaterClass loaded from C:\Development\Sample\build

 

Referenced By

In addition to showing locations and classes a class depends on, it is also possible to see which classes refer to a given class. In the above image you can see the class SomeInterface is referenced by blocked.BlocksALaterClass (which is located in the C:\Development\Sample\build folder).

Filtering

 
 
 
 

It is possible to apply filtering to the Classpath Helper view. Filtering will only show jars/folders/classes/packages that relate to selected filtering criteria.

The Location by Location View

The layout of this view initially appears identical to the ClasspathHelper view, however it is intended to show relationships between jars. The decorative icons are the same and essentially have the same meaning. But the Location by Location view can be used to view inter jar information.

This can be expanded in a similar fashion.

Depends On

The Depends on branch shows which jars/folders that this particular jar depends on. In this case ajar.jar depends on both the build and demoarea folders. Within each folder we can see the specific classes that are depended on.

Also notice the unreferenced icon . As with the classpath helper view, this indicates that the object is unreferenced. However in this view the icon indicates a jar that is not referenced at runtime by any other jar. This can be useful in locating obsolete jars.

Referenced By

The Referenced by Branch is the reverse of the depends on view. It shows which jars a particular jar supports or is referred to by. In this case, demoarea is referenced by itself and ajar.jar. The references are afolder.AClassWithDependencies and ajar.DependsOnFilesFromFolders. The specific class referenced isafolder.AClassWithNoDependencies which is refered to by both.

Unresolved

The unresolved branch is similar to unresolved branch from the ClassPath view. The only difference is that it is showing a summary of unresolved classes for the entire jar. In this case anunresolvedjar.ClassMissingFromJar cannot be found.

The Package View

This view takes a package centric view of the classpath, allowing you to look for classes without knowing or caring about the location of the class. The decorative icons are the same and have the same meaning as the other views.

Packages can be expanded to reveal the contents of a package.

Unresolved Classes

The highlighted region shows a package and class file decorated with a . This indicates that a reference to a class cannot be resolved (found) on the current classpath. In this example, a class called anunresolvedjar.ClassMissingFromJar cannot be found. At runtime this would lead to either a java.lang.ClassNotFoundException or a java.lang.NoClassDefFoundError. In either case, the class anunresolvedjar.ClassWithMissingDependency cannot be loaded.

Blocked (Obscured) Classes

The first highlighted region (next to the ) shows the class file DependsOnFilesFromFolder decorated with a . This indicates the class is 'blocked' or 'obscured' on the classpath. This means that the class/interface is available at multiple locations on the classpath. The list shows areas where this class is blocked.

The second highlighted region (next to the ) shows where the class would actually be loaded from.

Blocked (Obscured) Classes with different versions

The first highlighted region (next to the  shows the class BlocksALaterClass file with a . This indicates it is is 'blocked' or 'obscured' on the classpath. This is essentially the same as a yellow rectangle with one addition. The red color is also an indication that the version of the class at this location (C:\Development\Sample\demoarea in this example) is different from the version that will actually be loaded (from C:\Development\Sample\build in this example). As with a yellow rectangle, the folder shown below the blocked class is the location where the class will actually get loaded from.

As with the previous example, the second highlight  is showing the folder where the actual class will get loaded from. Of course blocking locations will always be above (appear earlier) in the classpath.

What a Class or Interface Depends On

In addition to showing issues or problems with the classpath, Classpath Helper also can be used to show what classes/interfaces a particular class depends on. The highlighted region shows that the class ajar.DependsOnFilesFromFolder depends on

• afolder.AClassWithNoDependencies loaded from C:\Development\Sample\demoarea
• blocked.BlocksALaterClass loaded from C:\Development\Sample\build

 

Referenced By

In addition to showing locations and classes a class depends on, it is also possible to see which classes refer to a given class. In the above image you can see the class SomeInterface is referenced by blocked.BlocksALaterClass (which is located in the C:\Development\Sample\build folder).

Filtering

 
 
 
 

It is possible to apply filtering to the Classpath Helper view. Filtering will only show jars/folders/classes/packages that relate to selected filtering criteria.

Not on Classpath View

This view scans for jars that are not on the classpath (but are under the current project). It provides basic browsing of packages and classes that are available but not on the classpath. This can be helpful when trying to build up a classpath, as you can quickly browse for the missing classes to see which jars contain them.

Available locations

The only information this view shows is which jars a class or interface can be loaded from. Only jars from the current Eclipse project that are not already on the classpath are scanned (this image was created by removing previously demoed jars from the classpath).

插件二：Classpath Checker
插件地址：http://classpathchecker.free.fr/


Classpath Checker @ Eclipse Plugin Central

 

Classpath Checker Eclipse Plugin v1.4.3

Description

1. The Classpath Checker eclipse plugin detects classpath inconsistencies in Java projects.
   
   That means it is able to:
2. Detect if a jar file is missing in your classpath. In case a class in your classpath depends on other classes that are not present in the classpath, the plugin warns you and gives you the missing class names.
3. Detect if you have some duplicated classes in all your jar files. In case of duplicated classes, this plugin warns you. If there are version conflicts in the duplicated classes, it helps you to determine which is the wrong Jar to remove from your classpath.

Why do I need this plugin?

As you know, current java projects depend of more and more external libraries, and 3rd party products. Obviously, each 3rd party product embeds its own libraries, consequently it becomes very difficult to be sure there are no classpath problems in the application. One terrible behavior is when the libraries order becomes important in the classpath! That's why Classpath Checker can help you.

Installation

1. This plugin has been tested on Eclipse 3.3.0 (Europa) only.
   
   To install the Classpath Checker plugin:
   Click here if you have the version (v1.1.0)
   
2. In Eclipse, click on Help -> Software Update -> Find and Install...
3. Choose the Search for new features to install option, and click Next.
4. Click New Remote Site.
5. Enter the following:
   • Name: Classpath Checker
   • URL: http://classpathchecker.free.fr/update-site
   and click OK.
6. "Classpath Checker" should appear under Sites to include in search. 
   Click the checkbox next to it to select it, and click Finish.
7. You should see Classpath Checker under Select features to install. 
   (You may have to click on one or two triangles to make it visible in the tree.) 
   Select the checkbox next to it and click next.
8. Select the I accept option to accept the license and click Next.
9. Make sure the location is correct where you're installing it. The default (your workspace) should be fine. Click Finish.
10. The plugin is not digitally signed. Go ahead and install it anyway.
11. Click Yes to make Eclipse restart itself.

How to use it?

After installing the plugin, you have to right click on your java project, then select "Properties".
The following dialog is displayed, select the "Classpath Checker" section, and then check the "Activate classpath checker".

评论

1 楼 大大灰狼 2014-10-22  

第一个不知道是不是我的Eclipse版本太高了，没法使用；
第二个不是清理jar包的吧...