[英]Java Bean: how <jsp:setProperty> in <jsp:useBean> is generated into Java Code
For example, I have this code: 例如,我有以下代码:
<jsp:useBean id="dog" class="Dog" scope="application">
<jsp:setProperty name="dog" property="breed" value="House Dog !!!"/>
</jsp:useBean>
I know how it works. 我知道它是如何工作的。 But, sometimes, I change some some code in this, for example: "dog" to "newDog", I will meet error or unguested-result (with me).
但是,有时,我会在其中更改一些代码,例如:将“ dog”更改为“ newDog”,我会遇到错误或毫无根据的结果。
Please give me how above code is generated into Java. 请给我上面的代码如何生成到Java中。 (maybe just a main idea)
(也许只是一个主意)
Thanks :) 谢谢 :)
JSPs ultimately get generated to .java
classes which get compiled as servlets. JSP最终生成为
.java
类,并作为servlet进行编译。 Check the server's work folder. 检查服务器的工作文件夹。 In case of Tomcat, a
/test.jsp
gets generated as /org/apache/jsp/test_jsp.java
file in Tomcat's /work
folder. 如果是Tomcat,
/test.jsp
在Tomcat的/work
文件夹/org/apache/jsp/test_jsp.java
作为/org/apache/jsp/test_jsp.java
文件生成。
The following lines 以下几行
<jsp:useBean id="dog" class="com.example.Dog" scope="application">
<jsp:setProperty name="dog" property="breed" value="House Dog !!!"/>
</jsp:useBean>
(the only change I made is adding a package; packageless classes are Bad™) (我所做的唯一更改是添加了一个程序包;无程序包类是Bad™)
are generated as 生成为
com.example.Dog dog = null;
synchronized (application) {
dog = (com.example.Dog) _jspx_page_context.getAttribute("dog", javax.servlet.jsp.PageContext.APPLICATION_SCOPE);
if (dog == null){
dog = new com.example.Dog();
_jspx_page_context.setAttribute("dog", dog, javax.servlet.jsp.PageContext.APPLICATION_SCOPE);
out.write("\n");
out.write(" ");
org.apache.jasper.runtime.JspRuntimeLibrary.introspecthelper(_jspx_page_context.findAttribute("dog"), "breed", "House Dog !!!", null, null, false);
out.write('\n');
}
}
Tomcat is open source, according to its source code, the JspRuntimeLibrary#introspecthelper()
method delegates to internalIntrospecthelper()
which ultimately does this: Tomcat是开放源代码,根据其源代码,
JspRuntimeLibrary#introspecthelper()
方法委托给internalIntrospecthelper()
最终实现此目的:
Method method = null;
Class<?> type = null;
Class<?> propertyEditorClass = null;
try {
java.beans.BeanInfo info
= java.beans.Introspector.getBeanInfo(bean.getClass());
if ( info != null ) {
java.beans.PropertyDescriptor pd[]
= info.getPropertyDescriptors();
for (int i = 0 ; i < pd.length ; i++) {
if ( pd[i].getName().equals(prop) ) {
method = pd[i].getWriteMethod();
type = pd[i].getPropertyType();
propertyEditorClass = pd[i].getPropertyEditorClass();
break;
}
}
}
if ( method != null ) {
if (type.isArray()) {
if (request == null) {
throw new JasperException(
Localizer.getMessage("jsp.error.beans.setproperty.noindexset"));
}
Class<?> t = type.getComponentType();
String[] values = request.getParameterValues(param);
//XXX Please check.
if(values == null) return;
if(t.equals(String.class)) {
method.invoke(bean, new Object[] { values });
} else {
createTypedArray (prop, bean, method, values, t,
propertyEditorClass);
}
} else {
if(value == null || (param != null && value.equals(""))) return;
Object oval = convert(prop, value, type, propertyEditorClass);
if ( oval != null )
method.invoke(bean, new Object[] { oval });
}
}
} catch (Exception ex) {
Throwable thr = ExceptionUtils.unwrapInvocationTargetException(ex);
ExceptionUtils.handleThrowable(thr);
throw new JasperException(ex);
}
You see, it's using java.beans.Introspector
to get bean information and properties by BeanInfo#getPropertyDescriptors()
. 您会看到,它使用
java.beans.Introspector
通过BeanInfo#getPropertyDescriptors()
获取bean信息和属性。 The desired <jsp:setProperty>
method is obtained as java.lang.reflect.Method
by PropertyDescriptor#getWriteMethod()
. 通过
PropertyDescriptor#getWriteMethod()
作为java.lang.reflect.Method
获得所需的<jsp:setProperty>
方法。 Finally it uses the Reflection API to invoke the method. 最后,它使用Reflection API调用该方法。
This is how it is generated: 它是这样生成的:
Dog dog = new Dog();
dog.setBreed("House Dog !!!");
The dog in setProperty is a reference to the Class Dog of useBean. setProperty中的dog是对useBean的类Dog的引用。 Hope you understand this
希望你能理解
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