JSP - TransformerFactory.newInstance().newTransformer(xsl) 返回 null？

发布于 2024-09-30 18:06:18 字数 3537 浏览 5 评论 0原文

java API 保证它永远不会返回 null - 但对我来说，它是！

http ://download.oracle.com/javase/6/docs/api/javax/xml/transform/TransformerFactory.html#newTransformer(javax.xml.transform.Source)

相关代码：

xml = new StreamSource(new URL(mondialURL).openStream());
xsl = new StreamSource(new File("/REMOVED/countriesnofilter.xsl"));
result = new StreamResult(new PrintWriter(out));

transformer = TransformerFactory.newInstance().newTransformer(xsl);
transformer.transform(xml, result);

由于xml、xsl和结果使用 new 制作的东西，它们必须包含非 null，所以它一定是转换器变成了 null。为什么会发生这种情况，我该如何解决它

：

org.apache.jasper.JasperException：JSP 中的异常：/ dca/ass2/a.jsp:46

43:  result = new StreamResult(new PrintWriter(out));
44:  
45:  transformer = TransformerFactory.newInstance().newTransformer(xsl);
46:  transformer.transform(xml, result);
47: 
48: %>
49:  <INPUT TYPE="SUBMIT" VALUE="Get one country">


Stacktrace:
 org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:451)
 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
 sun.reflect.GeneratedMethodAccessor50.invoke(Unknown Source)
 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 java.lang.reflect.Method.invoke(Method.java:597)
 org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244)
 java.security.AccessController.doPrivileged(Native Method)
 javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
 org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276)
 org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162)
root cause

java.lang.NullPointerException
 org.apache.jsp.dca.ass2.a_jsp._jspService(a_jsp.java:104)
 org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
 sun.reflect.GeneratedMethodAccessor50.invoke(Unknown Source)
 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 java.lang.reflect.Method.invoke(Method.java:597)
 org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244)
 java.security.AccessController.doPrivileged(Native Method)
 javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
 org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276)
 org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162)

编辑：变压器在某种程度上肯定为空。观看：

org.apache.jasper.JasperException：JSP 中的异常：/dca/ass2/a.jsp:49

46:     
47:     xml.getInputStream();
48:     xsl.getInputStream();
49:     transformer.reset();
50:     
51:     //transformer.transform(xml, result);
52:

这是一个再次出现空指针异常。如果是因为 xml 为空，那么它会在 47 处抛出 NPE

。 EDIT2：如果我将 newTransformer(xsl) 更改为 newTransformer() 它会起作用，所以这是 newTransformer(xsl) 中的问题。

原文

The java API guarantees that it will never return a null - but for me, it is!

http://download.oracle.com/javase/6/docs/api/javax/xml/transform/TransformerFactory.html#newTransformer(javax.xml.transform.Source)

Relevant code:

xml = new StreamSource(new URL(mondialURL).openStream());
xsl = new StreamSource(new File("/REMOVED/countriesnofilter.xsl"));
result = new StreamResult(new PrintWriter(out));

transformer = TransformerFactory.newInstance().newTransformer(xsl);
transformer.transform(xml, result);

Since xml, xsl and result were made something using new, they -must- contain not null, so it must be transformer that's becoming null. Why is this happening and how can I fix it?

Throws this:

org.apache.jasper.JasperException: Exception in JSP: /dca/ass2/a.jsp:46

43:  result = new StreamResult(new PrintWriter(out));
44:  
45:  transformer = TransformerFactory.newInstance().newTransformer(xsl);
46:  transformer.transform(xml, result);
47: 
48: %>
49:  <INPUT TYPE="SUBMIT" VALUE="Get one country">


Stacktrace:
 org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:451)
 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
 sun.reflect.GeneratedMethodAccessor50.invoke(Unknown Source)
 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 java.lang.reflect.Method.invoke(Method.java:597)
 org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244)
 java.security.AccessController.doPrivileged(Native Method)
 javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
 org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276)
 org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162)
root cause

java.lang.NullPointerException
 org.apache.jsp.dca.ass2.a_jsp._jspService(a_jsp.java:104)
 org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
 sun.reflect.GeneratedMethodAccessor50.invoke(Unknown Source)
 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 java.lang.reflect.Method.invoke(Method.java:597)
 org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244)
 java.security.AccessController.doPrivileged(Native Method)
 javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
 org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276)
 org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162)

EDIT: It is DEFINITELY the case that the transformer is null somehow. Watch:

org.apache.jasper.JasperException: Exception in JSP: /dca/ass2/a.jsp:49

46:     
47:     xml.getInputStream();
48:     xsl.getInputStream();
49:     transformer.reset();
50:     
51:     //transformer.transform(xml, result);
52:

And it's a null pointer exception again. If it was because xml was null then it would have thrown an NPE at 47.

EDIT2: If I change newTransformer(xsl) to newTransformer() it works, so it's a problem in newTransformer(xsl).

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无悔心 2024-10-07 18:06:18

在向项目添加新的依赖项后，当我的一些测试出错时，我遇到了同样的问题。想知道当 API 说不可能时，它怎么会返回 null，我再次修改了它：

“获取 TransformerFactory 的新实例。此静态方法创建一个新的工厂实例此方法使用以下顺序
查找过程以确定 TransformerFactory 实现
要加载的类：使用 javax.xml.transform.TransformerFactory 系统
财产。 ... [查找顺序] ... 一旦应用程序获得了
引用一个 TransformerFactory 它可以使用工厂来配置
并获取变压器实例。”

因此，我也查看了 TransformerFactory API，它说：

“确定要创建哪个 Factory 实现的系统属性名为“javax.xml.transform.TransformerFactory”。这
属性命名 TransformerFactory 抽象的具体子类
班级。如果未定义该属性，则平台默认值为
使用过。”

的，当我向项目添加新的依赖项时，问题就开始了：另一个处理 XML 文档/签名的项目。我删除了该依赖项，运行了测试（添加了依赖项后失败了）并检索了 TransformerFactory 的特定类。我重新添加了依赖项并再次运行测试：现在它是一个不同的类，因此，正如我所想，查找过程正在实例化错误的 TransformerFactory 实现，并在

我添加的 jar 中找到它。不想通过添加另一个系统属性来修复它，所以我像这样更改了代码：

private static final String TRANSFORMER_FACTORY_CLASS = "com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl";

TransformerFactory factory = TransformerFactory.newInstance(TRANSFORMER_FACTORY_CLASS, null);
//null for default ClassLoader

并且一切正常。

I ran into the same problem, when some of my tests went wrong, after having added a new dependency to the project. Wondering how could this return null when its API says it's impossible, I revised it again:

"Obtain a new instance of a TransformerFactory. This static method creates a new factory instance This method uses the following ordered
lookup procedure to determine the TransformerFactory implementation
class to load: Use the javax.xml.transform.TransformerFactory system
property. ... [lookup order] ... Once an application has obtained a
reference to a TransformerFactory it can use the factory to configure
and obtain transformer instances."

So, I had a look at TransformerFactory API, too, and it says:

"The system property that determines which Factory implementation to create is named "javax.xml.transform.TransformerFactory". This
property names a concrete subclass of the TransformerFactory abstract
class. If the property is not defined, a platform default is be
used."

As I mentioned, the problem started when I added a new dependency to the project: another project that processes XML documents/signatures. I deleted the dependency, ran the test (that failed with the dependency added) and retrieved the specific class of the TransformerFactory. I added the dependency back and ran the test again: it was a different class now. So, as I supposed, the lookup procedure was instantiating a wrong TransformerFactory implementation, finding it in the added jar.

I didn't want to fix it adding another system property, so I changed the code like that:

private static final String TRANSFORMER_FACTORY_CLASS = "com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl";

TransformerFactory factory = TransformerFactory.newInstance(TRANSFORMER_FACTORY_CLASS, null);
//null for default ClassLoader

and everything worked fine.

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