FreeMarker在JAVA中应用入门
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下面记录了一下简单的示例步骤:
1,创建一个XML模板:
- <?xml version="1.0" encoding="UTF-8"?>
- <people xmlns:h="http://www.w3.org/TR/html4/">
- <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
- 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@mail.com");
- 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.${val!""}的意思是如果val为null,取值"".
***Freemarker对XML文件中特殊字符的处理:通过<#escape>
- <#escape x as x?xml>
- <person id="000001" age="20">
- <name>
- <family>${p.fname}</family>
- <given>${p.gname}</given>
- </name>
- <email>${p.email}</email>
- <link manager="${p.manager}" />
- </person>
- </#escape>
val.setManager("m&an<ager"); 传入的值就按照XML规范保存到XML文件 link manager="m&an<ager" />
***循环处理 <#list>
- <#list people as p>
- <person id="000001" age="20">
- <name>
- <family>${p.fname}</family>
- <given>${p.gname}</given>
- </name>
- <email>${p.email}</email>
- <link manager="${p.manager}" />
- </person>
- </#list>
- List<ValueObject> pList = new ArrayList<ValueObject>();
- ValueObject val = null;
- val = new ValueObject();
- val.setFname("Yao");
- val.setGname("Yorker");
- val.setEmail("test@mail.com");
- val.setManager("m&an<ager");
- pList.add(val);
- val = new ValueObject();
- val.setFname("J");
- val.setGname("Jeremy");
- val.setEmail("test1@mail.com");
- val.setManager("m&an<ager");
- pList.add(val);
- parameters.put("people", pList);
***分支处理<#if>,根据值对模板做不同的输出.
<#if p.level == "L1">
<l1tag>xxx</l1tag>
</#if>
***对生成超大文件的测试:
- public void generateRequest(List<ValueObject> pList) {
- String reqFileName = "D:\\temp\\test.xml";
- try {
- Map<String, Object> parameters = new HashMap<String, Object>();
- parameters.put("people", pList);
- OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(reqFileName), "UTF-8");
- template.process(parameters, writer);
- writer.flush();
- } catch (IOException e) {
- e.printStackTrace();// TODO
- } catch (TemplateException e) {
- e.printStackTrace();// TODO
- }
- }
- public static void testLargeVolumn(){
- List<ValueObject> pList = new ArrayList<ValueObject>();
- ValueObject val = null;
- for(int i=0;i<400000;i++){
- val = new ValueObject();
- val.setFname("Yao"+i);
- val.setGname("Yorker");
- val.setEmail("test@mail.com");
- val.setManager("m&an<ager");
- val.setLevel("L"+i);
- pList.add(val);
- }
- new Test().generateRequest(pList);
- }
一次性输出,本例在达到循环400000次的时候异常:java.lang.OutOfMemoryError: Java heap space
解决办法:分多次输出到最终的输出文件中.
1,将模板需要循环的部分单独做成一个模板.
先一次输出循环模板前面的部分,分多次输出循环部分,一次输出循环部分之后的部分.
示例如下,(这里由于循环之前部分和之后部分不涉及模板替换,直接用JAVA代码输出)
模板需要循环输出的部分:
- <#escape x as x?xml>
- <#list people as p>
- <person id="000001" age="20">
- <name>
- <family>${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:
- 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.w3.org/TR/html4/\">");
- 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@mail.com");
- 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.
这里有FreeMarker的中文manual :http://download.csdn.net/user/kkdelta
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