Java的发展绝对离不开XML的贡献。
对于xml的定义文件通常使用dtd和xsd。xsd，dtd，tld有什么区别和联系？
我们重点描述一下关于校验的问题。
参考笔者多年前的问题spring 3.0如何增加无网络环境dtd文件免校验
我们看一下最常用的mybatis的xml是如何实现的
/**
* Offline entity resolver for the MyBatis DTDs
*
* @author Clinton Begin
*/
public class XMLMapperEntityResolver implements EntityResolver {
private static final Map<String, String> doctypeMap = new HashMap<String, String>();
private static final String IBATIS_CONFIG_PUBLIC = "-//ibatis.apache.org//DTD Config 3.0//EN".toUpperCase(Locale.ENGLISH);
private static final String IBATIS_CONFIG_SYSTEM = "http://ibatis.apache.org/dtd/ibatis-3-config.dtd".toUpperCase(Locale.ENGLISH);
private static final String IBATIS_MAPPER_PUBLIC = "-//ibatis.apache.org//DTD Mapper 3.0//EN".toUpperCase(Locale.ENGLISH);
private static final String IBATIS_MAPPER_SYSTEM = "http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd".toUpperCase(Locale.ENGLISH);
private static final String MYBATIS_CONFIG_PUBLIC = "-//mybatis.org//DTD Config 3.0//EN".toUpperCase(Locale.ENGLISH);
private static final String MYBATIS_CONFIG_SYSTEM = "http://mybatis.org/dtd/mybatis-3-config.dtd".toUpperCase(Locale.ENGLISH);
private static final String MYBATIS_MAPPER_PUBLIC = "-//mybatis.org//DTD Mapper 3.0//EN".toUpperCase(Locale.ENGLISH);
private static final String MYBATIS_MAPPER_SYSTEM = "http://mybatis.org/dtd/mybatis-3-mapper.dtd".toUpperCase(Locale.ENGLISH);
private static final String MYBATIS_CONFIG_DTD = "org/apache/ibatis/builder/xml/mybatis-3-config.dtd";
private static final String MYBATIS_MAPPER_DTD = "org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd";
static {
doctypeMap.put(IBATIS_CONFIG_SYSTEM, MYBATIS_CONFIG_DTD);
doctypeMap.put(IBATIS_CONFIG_PUBLIC, MYBATIS_CONFIG_DTD);
doctypeMap.put(IBATIS_MAPPER_SYSTEM, MYBATIS_MAPPER_DTD);
doctypeMap.put(IBATIS_MAPPER_PUBLIC, MYBATIS_MAPPER_DTD);
doctypeMap.put(MYBATIS_CONFIG_SYSTEM, MYBATIS_CONFIG_DTD);
doctypeMap.put(MYBATIS_CONFIG_PUBLIC, MYBATIS_CONFIG_DTD);
doctypeMap.put(MYBATIS_MAPPER_SYSTEM, MYBATIS_MAPPER_DTD);
doctypeMap.put(MYBATIS_MAPPER_PUBLIC, MYBATIS_MAPPER_DTD);
}
/*
* Converts a public DTD into a local one
*
* @param publicId The public id that is what comes after "PUBLIC"
* @param systemId The system id that is what comes after the public id.
* @return The InputSource for the DTD
*
* @throws org.xml.sax.SAXException If anything goes wrong
*/
@Override
public InputSource resolveEntity(String publicId, String systemId) throws SAXException {
if (publicId != null) {
publicId = publicId.toUpperCase(Locale.ENGLISH);
}
if (systemId != null) {
systemId = systemId.toUpperCase(Locale.ENGLISH);
}
InputSource source = null;
try {
String path = doctypeMap.get(publicId);
source = getInputSource(path, source);
if (source == null) {
path = doctypeMap.get(systemId);
source = getInputSource(path, source);
}
} catch (Exception e) {
throw new SAXException(e.toString());
}
return source;
}
private InputSource getInputSource(String path, InputSource source) {
if (path != null) {
InputStream in;
try {
in = Resources.getResourceAsStream(path);
source = new InputSource(in);
} catch (IOException e) {
// ignore, null is ok
}
}
return source;
}
}
当我们使用mybatis的时候通常会在xml中映射到
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
当xml解析的时候会在
org/apache/ibatis/builder/xml/mybatis-3-config.dtd
125927_xA0n_871390.png
由此可见就会正常的加载到。那么如果使用jar版本比较低而声明的xsd或dtd在jar中不能正确映射的话那么要去网络上获取该文件。
那么在网络不行的情况下（无网络）就会出现应用无法启动的问题了。解决方法自然要去查看一下报错的校验对应的声明和jar是否匹配。
如下是spring3.2的描述文件，因此如果使用了spring4的声明就会报错（无网络），通常jar提供者会兼容之前的dtd或xsd文件
http\://www.springframework.org/schema/aop/spring-aop-2.0.xsd=org/springframework/aop/config/spring-aop-2.0.xsd
http\://www.springframework.org/schema/aop/spring-aop-2.5.xsd=org/springframework/aop/config/spring-aop-2.5.xsd
http\://www.springframework.org/schema/aop/spring-aop-3.0.xsd=org/springframework/aop/config/spring-aop-3.0.xsd
http\://www.springframework.org/schema/aop/spring-aop-3.1.xsd=org/springframework/aop/config/spring-aop-3.1.xsd
http\://www.springframework.org/schema/aop/spring-aop-3.2.xsd=org/springframework/aop/config/spring-aop-3.2.xsd
http\://www.springframework.org/schema/aop/spring-aop.xsd=org/springframework/aop/config/spring-aop-3.2.xsd
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