一）什么是SpEL
SpEL -- Spring Expression Language. Spring的表达式语言。举个最简单的例子：

Java代码

1. ExpressionParser parser =new SpelExpressionParser();
2. Expression exp = parser.parseExpression("'Hello World'");
3. String message = (String) exp.getValue();

ExpressionParser parser =new SpelExpressionParser();
Expression exp = parser.parseExpression("'Hello World'");
String message = (String) exp.getValue();

最后 message的值就是 Hello World， 表达式中的单引号''就是表达String类型的一种格式。另外值得注意的一点时，当表达式不符合规范时， parser.parseExpression语句会抛出ParseException；而exp.getValue会抛出EvaluationException
而为了避免最后的类型转换，我们还可以这样写：

Java代码

1. String message = exp.getValue(String.class);

String message = exp.getValue(String.class);

二）SpEL举例中需要使用到的类
以下是本文介绍SpEL过程中需要使用到的类，在此列出，以供后续介绍中使用参考：
Inventor.java

Java代码

1. package org.spring.samples.spel.inventor;
2. import java.util.Date;
3. import java.util.GregorianCalendar;
4. public class Inventor {
5. private String name;
6. private String nationality;
7. private String[] inventions;
8. private Date birthdate;
9. private PlaceOfBirth placeOfBirth;
10. public Inventor(String name, String nationality){
11. GregorianCalendar c= new GregorianCalendar();
12. this.name = name;
13. this.nationality = nationality;
14. this.birthdate = c.getTime();
15. }
16. public Inventor(String name, Date birthdate, String nationality) {
17. this.name = name;
18. this.nationality = nationality;
19. this.birthdate = birthdate;
20. }
21. public Inventor() {}
22. public String getName() { return name;}
23. public void setName(String name) { this.name = name;}
24. public String getNationality() { return nationality;}
25. public void setNationality(String nationality) { this.nationality = nationality; }
26. public Date getBirthdate() { return birthdate;}
27. public void setBirthdate(Date birthdate) { this.birthdate = birthdate;}
28. public PlaceOfBirth getPlaceOfBirth() { return placeOfBirth;}
29. public void setPlaceOfBirth(PlaceOfBirth placeOfBirth) { this.placeOfBirth = placeOfBirth;}
30. public void setInventions(String[] inventions) { this.inventions = inventions; }
31. public String[] getInventions() { return inventions;}
32. }

package org.spring.samples.spel.inventor;
import java.util.Date;
import java.util.GregorianCalendar;public class Inventor {private String name;private String nationality;private String[] inventions;private Date birthdate;private PlaceOfBirth placeOfBirth;public Inventor(String name, String nationality){GregorianCalendar c= new GregorianCalendar();this.name = name;this.nationality = nationality;this.birthdate = c.getTime();}public Inventor(String name, Date birthdate, String nationality) {this.name = name;this.nationality = nationality;this.birthdate = birthdate;}public Inventor() {}public String getName() { return name;}public void setName(String name) { this.name = name;}public String getNationality() { return nationality;}public void setNationality(String nationality) { this.nationality = nationality; }public Date getBirthdate() { return birthdate;}public void setBirthdate(Date birthdate) { this.birthdate = birthdate;}public PlaceOfBirth getPlaceOfBirth() { return placeOfBirth;}public void setPlaceOfBirth(PlaceOfBirth placeOfBirth) { this.placeOfBirth = placeOfBirth;}public void setInventions(String[] inventions) { this.inventions = inventions; }public String[] getInventions() { return inventions;}
}

PlaceOfBirth.java

Java代码

1. package org.spring.samples.spel.inventor;
2. public class PlaceOfBirth {
3. private String city;
4. private String country;
5. public PlaceOfBirth(String city) {this.city=city;}
6. public PlaceOfBirth(String city, String country){
7. this(city);
8. this.country = country;
9. }
10. public String getCity() {return city;}
11. public void setCity(String s) {this.city = s;}
12. public String getCountry() {return country;}
13. public void setCountry(String country) {this.country = country;}
14. }

package org.spring.samples.spel.inventor;public class PlaceOfBirth {private String city;private String country;public PlaceOfBirth(String city) {this.city=city;}public PlaceOfBirth(String city, String country){this(city);this.country = country;}public String getCity() {return city;}public void setCity(String s) {this.city = s;}public String getCountry() {return country;}public void setCountry(String country) {this.country = country;}
}

Society.java

Java代码

1. package org.spring.samples.spel.inventor;
2. import java.util.*;
3. public class Society {
4. private String name;
5. public static String Advisors = "advisors";
6. public static String President = "president";
7. private List<Inventor> members = new ArrayList<Inventor>();
8. private Map officers = new HashMap();
9. public List getMembers() {return members;}
10. public Map getOfficers() {return officers;}
11. public String getName() {return name;}
12. public void setName(String name) {this.name = name;}
13. public boolean isMember(String name){
14. boolean found = false;
15. for (Inventor inventor : members) {
16. if (inventor.getName().equals(name)){
17. found = true;
18. break;
19. }
20. }
21. return found;
22. }
23. }

package org.spring.samples.spel.inventor;
import java.util.*;public class Society {private String name;public static String Advisors = "advisors";public static String President = "president";private List<Inventor> members = new ArrayList<Inventor>();private Map officers = new HashMap();public List getMembers() {return members;}public Map getOfficers() {return officers;}public String getName() {return name;}public void setName(String name) {this.name = name;}public boolean isMember(String name){boolean found = false;for (Inventor inventor : members) {if (inventor.getName().equals(name)){found = true;break;}}return found;}
}