Spring --- SpEL

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

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

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

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;}
}

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

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;}
}

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

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;
}
}

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;
  }
}