FreeMarker在JAVA中应用入门
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'(${}),生成最终的XML文件.下面记录了一下简单的示例步骤:
1,创建一个XML模板:www.
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<?xml version="1.0" encoding="UTF-8"?>
<people xmlns:h="http://www.
<person id="000001" age="20">
<name>
<family>${p.fname}</family>
<given>${p.gname}</given>
</name>
<email>${p.email}</email>
<link manager="${p.manager}" />
</person>
</people>
2,在JAVA中将mark用值替换掉:下面是JAVA代码
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package com.test.xml.freemarker;
public class ValueObject {
private String fname;
private String gname;
private String email;
private String manager;
public String getFname() {
return fname;
}
public void setFname(String fname) {
this.fname = fname;
}
public String getGname() {
return gname;
}
public void setGname(String gname) {
this.gname = gname;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getManager() {
return manager;
}
public void setManager(String manager) {
this.manager = manager;
}
}
public class Test {
Configuration freeMarkerCfg = new Configuration();
Template template = null;
public Test() {
freeMarkerCfg.setClassForTemplateLoading(getClass(),"");
freeMarkerCfg.setObjectWrapper(new DefaultObjectWrapper());
try {
template = freeMarkerCfg.getTemplate("test.xml");
} catch (IOException e) {
// TODO
e.printStackTrace();
}
}
public void generateRequest(ValueObject obj) {
String reqFileName = "D:\\temp\\test.xml";
try {
Map<String, Object> parameters = new HashMap<String, Object>();
parameters.put("p", obj);
OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName), "UTF-8");
template.process(parameters, writer);
writer.flush();
} catch (IOException e) {
e.printStackTrace();// TODO
} catch (TemplateException e) {
e.printStackTrace();// TODO
}
}
public static void main(String[] args) {
ValueObject val = new ValueObject();
val.setFname("Yao");
val.setGname("Yorker");
val.setEmail("test@);
val.setManager("manager");
new Test().generateRequest(val);
}
}
XML模板和class在package "com.test.xml.freemarker".
***在模板中通过${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>
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<#escape x as x?xml>
<person id="000001" age="20">
<name>
<family>${p.fname}</family>
<given>${p.gname}</given>
</name>
<email>${p.email}</email>
<link manager="${p.manager}" />
</person>
</#escape>
val.setManager("m&an<ager"); 传入的值就按照XML规范保存到XML文件 link manager="m&an<ager" />
***循环处理 <#list>
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<#list people as p>
<person id="000001" age="20">
<name>
<family>${p.fname}</family>
<given>${p.gname}</given>
</name>
<email>${p.email}</email>
<link manager="${p.manager}" />
</person>
</#list>
List<ValueObject> pList = new ArrayList<ValueObject>();
ValueObject val = null;
val = new ValueObject();
val.setFname("Yao");
val.setGname("Yorker");
val.setEmail("test@);
val.setManager("m&an<ager");
pList.add(val);
val = new ValueObject();
val.setFname("J");
val.setGname("Jeremy");
val.setEmail("test1@);
val.setManager("m&an<ager");
pList.add(val);
parameters.put("people", pList);
***分支处理<#if>,根据值对模板做不同的输出.
<#if p.level == "L1">
<l1tag>xxx</l1tag>
</#if>
***对生成超大文件的测试:
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public void generateRequest(List<ValueObject> pList) {
String reqFileName = "D:\\temp\\test.xml";
try {
Map<String, Object> parameters = new HashMap<String, Object>();
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<ValueObject> pList = new ArrayList<ValueObject>();
ValueObject val = null;
for(int i=0;i<400000;i++){
val = new ValueObject();
val.setFname("Yao"+i);
val.setGname("Yorker");
val.setEmail("test@);
val.setManager("m&an<ager");
val.setLevel("L"+i);
pList.add(val);
}
new Test().generateRequest(pList);
}
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:
[html] view plaincopyprint?
<#escape x as x?xml>
<#list people as p>
<person id="000001" age="20">
<name>
<family>${p.fname}</family>
<given>${p.gname}</given>
</name>
<email>${p.email}</email>
<link manager="${p.manager}" />
<#if p.level == "L1">
<l1tag>xxx</l1tag>
</#if>
</person>
</#list>
</#escape>
JAVA代码:
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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("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
writer.write("<people xmlns:h=\"http://www.\">");
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("</people>");
writer.flush();
} catch (IOException e) {
e.printStackTrace();// TODO
}
}
public void generateRequest(List<ValueObject> pList) {
String reqFileName = "D:\\temp\\test.xml";
try {
Map<String, Object> parameters = new HashMap<String, Object>();
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<ValueObject> pList = new ArrayList<ValueObject>();
ValueObject val = null;
int i=0;
for(;i<500000;i++){
val = new ValueObject();
val.setFname("Yao"+i);
val.setGname("Yorker");
val.setEmail("test@);
val.setManager("m&an<ager");
val.setLevel("L"+i);
pList.add(val);
if(i%10000==0){
generateRequest(pList);
pList.clear();
}
}
if(i%10000!=0){
generateRequest(pList);
}
generateRequestTail();
}
public static void main(String[] args) {
new LargeVolumnTest().testLargeVolumn();
}
}
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.www.
