JXL Web 应用性能问题 转载

1. JXL核心组件中存在两个致命的性能问题：

1.1. 使用JXL不可避免地会遇到大对象请求的现象。

jxl.write.biff.File和jxl.read.biff.File构造方法中缺省创建的5兆大小原始类型数组，并不是业务场景运行必须，我们应该可以使此原始类型数组缺省大小减小，从而减小对JVM内存管理的压力，提高系统的稳定性。进一步分析jxl.write.biff.File和jxl.read.biff.File源代码：

package jxl.write.biff; … public final class File { File(OutputStream os, WorkbookSettings ws) { initialFileSize = ws.getInitialFileSize(); arrayGrowSize = ws.getArrayGrowSize(); data = new byte[initialFileSize]; pos = 0; outputStream = os; workbookSettings = ws; } … } package jxl.read.biff; … public final class File { File(InputputStream is, WorkbookSettings ws) { workbookSettings = ws; initialFileSize = workbookSettings.getInitialFileSize(); arrayGrowSize = workbookSettings.getArrayGrowSize(); byte d[] = new byte[initialFileSize]; int bytesRead = is.read(d); int pos = bytesRead; } … }  正如我们初期判断，在File构造方法中，创建数组大小为initialFileSize的byte[]数组，而initialFileSize由jxl. WorkbookSettings类对象中定义，如以下代码： package jxl; …… public final class WorkbookSettings { private int initialFileSize; private int arrayGrowSize; private boolean gcDisabled; …… public WorkbookSettings() { initialFileSize = 5242880; arrayGrowSize = 1048576; localeFunctionNames = new HashMap(); …… gcDisabled = Boolean.getBoolean(”jxl.nogc”); …… } public void setArrayGrowSize(int sz) { arrayGrowSize = sz; } public int getArrayGrowSize() { return arrayGrowSize; } public void setInitialFileSize(int sz) { initialFileSize = sz; } public int getInitialFileSize() { return initialFileSize; } public boolean getGCDisabled() { return gcDisabled; } …… }  其中定义的系统缺省initialFileSize大小为5242880，而单个byte大小为一个字节，从此我们可以断定在jxl.write.biff.File和jxl.read.biff.File构造方法中会缺省创建了一个5兆大小的大对象 byte[5242880]

 

1.2. JXL核心代码中过度使用System.gc()方法，增加CPU负荷。在jxl.write.biff.File类对象方法colse和WorkbookParser类对象方法close中，对系统JVM垃圾回收进行了强制垃圾回收，在J2EE应用服务器中，我们是极力反对这种应用调度GC的做法，此种操作会极度影响系统性能和稳定性。 package jxl.write.biff; ….. public final class File { …… void close(boolean cs) throws IOException { …… if(!workbookSettings.getGCDisabled()) System.gc(); } …… } package jxl.read.biff; ….. public final class WorkbookParser { …… public void close() { if (lastSheet != null) lastSheet.clear(); excelFile.clear(); if (!settings.getGCDisabled()) System.gc(); } …… }

 

 

 2. 针对Excel生成组件JXL大对象和System.gc问题的修订在jxl.WorkbookSettings类中进行如下代码修订 package jxl; …… public final class WorkbookSettings { public WorkbookSettings() { initialFileSize = 5242880; initialFileSize = 204800; //初始化Excel创建对象数组为200K arrayGrowSize = 1048576; arrayGrowSize = 204800; //对象数组不够用时，数组大小增长200K localeFunctionNames = new HashMap(); try { boolean suppressWarnings = Boolean.getBoolean(”jxl.nowarnings”); setSuppressWarnings(suppressWarnings); drawingsDisabled = Boolean.getBoolean(”jxl.nodrawings”); namesDisabled = Boolean.getBoolean(”jxl.nonames”); gcDisabled = Boolean.getBoolean(“jxl.nogc”); gcDisabled = true; //设置不允许进行任何应用层调度JVM进行垃圾回收 rationalizationDisabled = Boolean.getBoolean(”jxl.norat”); …… } } …… } 

也可以通过，

WorkbookSettings ws = new WorkbookSettings();

ws.setInitialFileSize(200*1024);

ws.setGCDisabled(true);

ws.setArrayGrowSize(512*1024);

book = Workbook.getWorkbook(file,ws);

来进行设置

原文链接：http://hi.baidu.com/deathoracle/blog/item/4a64d002b2fa807d3812bb13.html