在项目中通常有生成XML文件发送到另一个系统的需求,简单的办法可以是用一个XML模板,通过Freemarker替换其中的'Mark'(${}),生成最终的XML文件.
下面记录了一下简单的示例步骤:
1,创建一个XML模板:
${p.fname}
${p.gname}
${p.email}
2,在Java中将mark用值替换掉:下面是JAVA代码
package com.test.xml.freemarker;
public class ValueObject {
private String fname;
private String gname;
private String email;
private String manager;
public String getFname() {
return fname;
}
public void setFname(String fname) {
this.fname = fname;
}
public String getGname() {
return gname;
}
public void setGname(String gname) {
this.gname = gname;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getManager() {
return manager;
}
public void setManager(String manager) {
this.manager = manager;
}
}
public class Test {
Configuration freeMarkerCfg = new Configuration();
Template template = null;
public Test() {
freeMarkerCfg.setClassForTemplateLoading(getClass(),"");
freeMarkerCfg.setObjectWrapper(new DefaultObjectWrapper());
try {
template = freeMarkerCfg.getTemplate("test.xml");
} catch (IOException e) {
// TODO
e.printStackTrace();
}
}
public void generateRequest(ValueObject obj) {
String reqFileName = "D:\\temp\\test.xml";
try {
Map parameters = new HashMap();
parameters.put("p", obj);
OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName), "UTF-8");
template.process(parameters, writer);
writer.flush();
} catch (IOException e) {
e.printStackTrace();// TODO
} catch (TemplateException e) {
e.printStackTrace();// TODO
}
}
public static void main(String[] args) {
ValueObject val = new ValueObject();
val.setFname("Yao");
val.setGname("Yorker");
val.setEmail("[email protected]");
val.setManager("manager");
new Test().generateRequest(val);
}
}
XML模板和class在package "com.test.xml.freemarker".
***在模板中通过${val}指定的值,如果在处理的时候val值为null,会出现下面的异常:
freemarker.core.InvalidReferenceException: Expression valis undefined on line 46, column 63 in test.ftl
FreeMarker这么做的本意是防止在传值的地方(Data Model)写入的参数,如想传入 parameters.put("abc", obj);,但是写成了parameters.put("abcd", obj);
但是有的时候,里面有的值不是必须有值的,可以通过${val!""}来绕过这个异常.${val!""}的意思是如果val为null,取值"".
***Freemarker对XML文件中特殊字符的处理:通过<#escape>
<#escape x as x?xml>
${p.fname}
${p.gname}
${p.email}
val.setManager("m&an
***循环处理 <#list>
<#list people as p>
${p.fname}
${p.gname}
${p.email}
List pList = new ArrayList();
ValueObject val = null;
val = new ValueObject();
val.setFname("Yao");
val.setGname("Yorker");
val.setEmail("[email protected]");
val.setManager("m&an ***分支处理<#if>,根据值对模板做不同的输出.
<#if p.level == "L1">
xxx
***对生成超大文件的测试:
public void generateRequest(List pList) {
String reqFileName = "D:\\temp\\test.xml";
try {
Map parameters = new HashMap();
parameters.put("people", pList);
OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName), "UTF-8");
template.process(parameters, writer);
writer.flush();
} catch (IOException e) {
e.printStackTrace();// TODO
} catch (TemplateException e) {
e.printStackTrace();// TODO
}
}
public static void testLargeVolumn(){
List pList = new ArrayList();
ValueObject val = null;
for(int i=0;i<400000;i++){
val = new ValueObject();
val.setFname("Yao"+i);
val.setGname("Yorker");
val.setEmail("[email protected]");
val.setManager("m&an 一次性输出,本例在达到循环400000次的时候异常:java.lang.OutOfMemoryError: Java heap space
解决办法:分多次输出到最终的输出文件中.
1,将模板需要循环的部分单独做成一个模板.
先一次输出循环模板前面的部分,分多次输出循环部分,一次输出循环部分之后的部分.
示例如下,(这里由于循环之前部分和之后部分不涉及模板替换,直接用JAVA代码输出)
模板需要循环输出的部分:
<#escape x as x?xml>
<#list people as p>
${p.fname}
${p.gname}
${p.email}
<#if p.level == "L1">
xxx
JAVA代码:
public class LargeVolumnTest {
Configuration freeMarkerCfg = new Configuration();
Template template = null;
public LargeVolumnTest() {
freeMarkerCfg.setClassForTemplateLoading(getClass(),"");
freeMarkerCfg.setObjectWrapper(new DefaultObjectWrapper());
try {
template = freeMarkerCfg.getTemplate("testL.xml");
} catch (IOException e) {
// TODO
e.printStackTrace();
}
}
public void generateRequestHeader() {
String reqFileName = "D:\\temp\\test.xml";
try {
OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName), "UTF-8");
writer.write("");
writer.write("");
writer.flush();
} catch (IOException e) {
e.printStackTrace();// TODO
}
}
public void generateRequestTail() {
String reqFileName = "D:\\temp\\test.xml";
try {
OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName,true), "UTF-8");
writer.write(" ");
writer.flush();
} catch (IOException e) {
e.printStackTrace();// TODO
}
}
public void generateRequest(List pList) {
String reqFileName = "D:\\temp\\test.xml";
try {
Map parameters = new HashMap();
parameters.put("people", pList);
OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName,true), "UTF-8");
template.process(parameters, writer);
writer.flush();
} catch (IOException e) {
e.printStackTrace();// TODO
} catch (TemplateException e) {
e.printStackTrace();// TODO
}
}
public void testLargeVolumn(){
generateRequestHeader();
List pList = new ArrayList();
ValueObject val = null;
int i=0;
for(;i<500000;i++){
val = new ValueObject();
val.setFname("Yao"+i);
val.setGname("Yorker");
val.setEmail("[email protected]");
val.setManager("m&an 注意在输出循环部分和结尾部分是通过追加到文件的方式:OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName,true), "UTF-8");
最终生成的XML文档有90M,没有报异常.
这里有FreeMarker的中文manual :http://download.csdn.net/user/kkdelta