Java&Xml教程（十）XML作为属性文件使用
属性文件
我们通常会将Java应用的配置参数保存在属性文件中，Java应用的属性文件可以是一个正常的基于key-value对,以properties为扩展名的文件，也可以是XML文件.
在本案例中，將会向大家介绍如何通过Java程序输出这两种格式的属性文件，并介绍如何从classpath中加载和使用这两种属性文件。
下面是案例程序代码：
PropertyFilesUtil.java
package com.journaldev.util;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import java.util.Set;
public class PropertyFilesUtil {
public static void main(String[] args) throws IOException {
String propertyFileName = "DB.properties";
String xmlFileName = "DB.xml";
writePropertyFile(propertyFileName, xmlFileName);
readPropertyFile(propertyFileName, xmlFileName);
readAllKeys(propertyFileName, xmlFileName);
readPropertyFileFromClasspath(propertyFileName);
} /**
* read property file from classpath
* @param propertyFileName
* @throws IOException
*/
private static void readPropertyFileFromClasspath(String propertyFileName) throws IOException {
Properties prop = new Properties();
prop.load(PropertyFilesUtil.class.getClassLoader().getResourceAsStream(propertyFileName));
System.out.println(propertyFileName +" loaded from Classpath::db.host = "+prop.getProperty("db.host"));
System.out.println(propertyFileName +" loaded from Classpath::db.user = "+prop.getProperty("db.user"));
System.out.println(propertyFileName +" loaded from Classpath::db.pwd = "+prop.getProperty("db.pwd"));
System.out.println(propertyFileName +" loaded from Classpath::XYZ = "+prop.getProperty("XYZ"));
} /**
* read all the keys from the given property files
* @param propertyFileName
* @param xmlFileName
* @throws IOException
*/
private static void readAllKeys(String propertyFileName, String xmlFileName) throws IOException {
System.out.println("Start of readAllKeys");
Properties prop = new Properties();
FileReader reader = new FileReader(propertyFileName);
prop.load(reader);
Set<Object> keys= prop.keySet(); for(Object obj : keys){
System.out.println(propertyFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
} //loading xml file now, first clear existing properties
prop.clear();
InputStream is = new FileInputStream(xmlFileName);
prop.loadFromXML(is);
keys= prop.keySet(); for(Object obj : keys){
System.out.println(xmlFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
} //Now free all the resources
is.close();
reader.close();
System.out.println("End of readAllKeys");
} /**
* This method reads property files from file system
* @param propertyFileName
* @param xmlFileName
* @throws IOException
* @throws FileNotFoundException
*/
private static void readPropertyFile(String propertyFileName, String xmlFileName) throws FileNotFoundException, IOException {
System.out.println("Start of readPropertyFile");
Properties prop = new Properties();
FileReader reader = new FileReader(propertyFileName);
prop.load(reader);
System.out.println(propertyFileName +"::db.host = "+prop.getProperty("db.host"));
System.out.println(propertyFileName +"::db.user = "+prop.getProperty("db.user"));
System.out.println(propertyFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
System.out.println(propertyFileName +"::XYZ = "+prop.getProperty("XYZ"));
//loading xml file now, first clear existing properties
prop.clear();
InputStream is = new FileInputStream(xmlFileName);
prop.loadFromXML(is);
System.out.println(xmlFileName +"::db.host = "+prop.getProperty("db.host"));
System.out.println(xmlFileName +"::db.user = "+prop.getProperty("db.user"));
System.out.println(xmlFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
System.out.println(xmlFileName +"::XYZ = "+prop.getProperty("XYZ"));
//Now free all the resources
is.close();
reader.close();
System.out.println("End of readPropertyFile");
} /**
* This method writes Property files into file system in property file
* and xml format
* @param fileName
* @throws IOException
*/
private static void writePropertyFile(String propertyFileName, String xmlFileName) throws IOException {
System.out.println("Start of writePropertyFile");
Properties prop = new Properties();
prop.setProperty("db.host", "localhost");
prop.setProperty("db.user", "user");
prop.setProperty("db.pwd", "password");
prop.store(new FileWriter(propertyFileName), "DB Config file");
System.out.println(propertyFileName + " written successfully");
prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");
System.out.println(xmlFileName + " written successfully");
System.out.println("End of writePropertyFile");
}
}登录后复制
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当运行这段代码时，writePropertyFile 方法会在生成上述两种格式的属性文件，并將文件存储在工程的根目录下。
writePropertyFile 方法生成的两种属性文件内容：
DB.properties
#DB Config file#Fri Nov 16 11:16:37 PST 2012db.user=user db.host=localhost db.pwd=password
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DB.xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?><!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"><properties><comment>DB Config XML file</comment> <entry key="db.user">user</entry><entry key="db.host">localhost</entry><entry key="db.pwd">password</entry> </properties>
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需要注意的是comment元素，我们在使用prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");这段代码时第二个参数传入的是注释内容，如果传入null，生成的xml属性文件將没有comment元素。
控制台输出内容如下：
Start of writePropertyFile
DB.properties written successfully
DB.xml written successfully
End of writePropertyFile
Start of readPropertyFileDB.properties::db.host = localhostDB.properties::db.user =
userDB.properties::db.pwd = passwordDB.properties::XYZ = nullDB.xml::db.host =
localhostDB.xml::db.user = userDB.xml::db.pwd = passwordDB.xml::XYZ = null
End of readPropertyFile
Start of readAllKeysDB.properties:: Key=db.user::value=userDB.properties::
Key=db.host::value=localhostDB.properties:: Key=db.pwd::value=passwordDB.xml:: Key=db.user::value=userDB.xml::
Key=db.host::value=localhostDB.xml:: Key=db.pwd::value=password
End of readAllKeys
Exception in thread "main" java.lang.NullPointerException
at java.util.Properties$LineReader.readLine(Properties.java:434)
at java.util.Properties.load0(Properties.java:353)
at java.util.Properties.load(Properties.java:341)
at com.journaldev.util.PropertyFilesUtil.readPropertyFileFromClasspath(PropertyFilesUtil.java:31)
at com.journaldev.util.PropertyFilesUtil.main(PropertyFilesUtil.java:21)登录后复制
这里报了空指针异常，原因是生成的文件保存在工程的根目录下面，而读取时是从classpath下读取，將上面生成的两个属性文件拷贝到src下再次运行程序即可。
我们通常会将Java应用的配置参数保存在属性文件中，Java应用的属性文件可以是一个正常的基于key-value对,以properties为扩展名的文件，也可以是XML文件.
在本案例中，將会向大家介绍如何通过Java程序输出这两种格式的属性文件，并介绍如何从classpath中加载和使用这两种属性文件。
下面是案例程序代码：
PropertyFilesUtil.java
package com.journaldev.util;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import java.util.Set;
public class PropertyFilesUtil {
public static void main(String[] args) throws IOException {
String propertyFileName = "DB.properties";
String xmlFileName = "DB.xml";
writePropertyFile(propertyFileName, xmlFileName);
readPropertyFile(propertyFileName, xmlFileName);
readAllKeys(propertyFileName, xmlFileName);
readPropertyFileFromClasspath(propertyFileName);
} /**
* read property file from classpath
* @param propertyFileName
* @throws IOException
*/
private static void readPropertyFileFromClasspath(String propertyFileName) throws IOException {
Properties prop = new Properties();
prop.load(PropertyFilesUtil.class.getClassLoader().getResourceAsStream(propertyFileName));
System.out.println(propertyFileName +" loaded from Classpath::db.host = "+prop.getProperty("db.host"));
System.out.println(propertyFileName +" loaded from Classpath::db.user = "+prop.getProperty("db.user"));
System.out.println(propertyFileName +" loaded from Classpath::db.pwd = "+prop.getProperty("db.pwd"));
System.out.println(propertyFileName +" loaded from Classpath::XYZ = "+prop.getProperty("XYZ"));
} /**
* read all the keys from the given property files
* @param propertyFileName
* @param xmlFileName
* @throws IOException
*/
private static void readAllKeys(String propertyFileName, String xmlFileName) throws IOException {
System.out.println("Start of readAllKeys");
Properties prop = new Properties();
FileReader reader = new FileReader(propertyFileName);
prop.load(reader);
Set<Object> keys= prop.keySet(); for(Object obj : keys){
System.out.println(propertyFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
} //loading xml file now, first clear existing properties
prop.clear();
InputStream is = new FileInputStream(xmlFileName);
prop.loadFromXML(is);
keys= prop.keySet(); for(Object obj : keys){
System.out.println(xmlFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
} //Now free all the resources
is.close();
reader.close();
System.out.println("End of readAllKeys");
} /**
* This method reads property files from file system
* @param propertyFileName
* @param xmlFileName
* @throws IOException
* @throws FileNotFoundException
*/
private static void readPropertyFile(String propertyFileName, String xmlFileName) throws FileNotFoundException, IOException {
System.out.println("Start of readPropertyFile");
Properties prop = new Properties();
FileReader reader = new FileReader(propertyFileName);
prop.load(reader);
System.out.println(propertyFileName +"::db.host = "+prop.getProperty("db.host"));
System.out.println(propertyFileName +"::db.user = "+prop.getProperty("db.user"));
System.out.println(propertyFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
System.out.println(propertyFileName +"::XYZ = "+prop.getProperty("XYZ"));
//loading xml file now, first clear existing properties
prop.clear();
InputStream is = new FileInputStream(xmlFileName);
prop.loadFromXML(is);
System.out.println(xmlFileName +"::db.host = "+prop.getProperty("db.host"));
System.out.println(xmlFileName +"::db.user = "+prop.getProperty("db.user"));
System.out.println(xmlFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
System.out.println(xmlFileName +"::XYZ = "+prop.getProperty("XYZ"));
//Now free all the resources
is.close();
reader.close();
System.out.println("End of readPropertyFile");
} /**
* This method writes Property files into file system in property file
* and xml format
* @param fileName
* @throws IOException
*/
private static void writePropertyFile(String propertyFileName, String xmlFileName) throws IOException {
System.out.println("Start of writePropertyFile");
Properties prop = new Properties();
prop.setProperty("db.host", "localhost");
prop.setProperty("db.user", "user");
prop.setProperty("db.pwd", "password");
prop.store(new FileWriter(propertyFileName), "DB Config file");
System.out.println(propertyFileName + " written successfully");
prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");
System.out.println(xmlFileName + " written successfully");
System.out.println("End of writePropertyFile");
}
}登录后复制
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当运行这段代码时，writePropertyFile 方法会在生成上述两种格式的属性文件，并將文件存储在工程的根目录下。
writePropertyFile 方法生成的两种属性文件内容：
DB.properties
#DB Config file#Fri Nov 16 11:16:37 PST 2012db.user=user db.host=localhost db.pwd=password
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DB.xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?><!DOCTYPE properties SYSTEM " <properties><comment>DB Config XML file</comment><entry key="db.user">user</entry><entry key="db.host">localhost</entry> <entry key="db.pwd">password</entry></properties>
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需要注意的是comment元素，我们在使用prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");这段代码时第二个参数传入的是注释内容，如果传入null，生成的xml属性文件將没有comment元素。
控制台输出内容如下：
Start of writePropertyFile
DB.properties written successfully
DB.xml written successfully
End of writePropertyFile
Start of readPropertyFileDB.properties::db.host = localhostDB.properties::db.user = userDB.properties::db.pwd = passwordDB.properties::XYZ =
nullDB.xml::db.host = localhostDB.xml::db.user = userDB.xml::db.pwd = passwordDB.xml::XYZ = null
End of readPropertyFile
Start of readAllKeysDB.properties:: Key=db.user::value=userDB.properties:: Key=db.host::value=localhostDB.properties:: Key=db.pwd::value=passwordDB.xml::
Key=db.user::value=userDB.xml:: Key=db.host::value=localhostDB.xml:: Key=db.pwd::value=password
End of readAllKeys
Exception in thread "main" java.lang.NullPointerException
at java.util.Properties$LineReader.readLine(Properties.java:434)
at java.util.Properties.load0(Properties.java:353)
at java.util.Properties.load(Properties.java:341)
at com.journaldev.util.PropertyFilesUtil.readPropertyFileFromClasspath(PropertyFilesUtil.java:31)
at com.journaldev.util.PropertyFilesUtil.main(PropertyFilesUtil.java:21)登录后复制
以上就是Java&Xml教程（十）XML作为属性文件使用的内容，更多相关内容请关注PHP中文网（www.php.cn）！
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