Google Guava集合在实体类中的应用示例

将实体list，转换成map，拿到所有id的集合方法。减少访问数据库。

实体基类BaseEntity

package com.mytest;    import org.apache.commons.lang3.builder.ToStringBuilder;  import org.apache.commons.lang3.builder.ToStringStyle;    public class BaseEntity {   private Long id;   public Long getId() {    return id;   }   public void setId(Long id) {    this.id = id;   }   /**    * 覆盖toString方法，目的显示所有JavaBean的属性值，省略写很多的getXxx的方法    */   public String toString() {    return ToStringBuilder.reflectionToString(this,      ToStringStyle.MULTI_LINE_STYLE);   }  }

实体类Person

package com.mytest;      public class Person extends BaseEntity{      private String name;   private String gender;   private int age;   private double weight;      public Person(Long id, String name, String gender, int age, double weight) {    super();    this.setId(id);    this.name = name;    this.gender = gender;    this.age = age;    this.weight = weight;   }   public String getName() {    return name;   }   public void setName(String name) {    this.name = name;   }     public String getGender() {    return gender;   }     public void setGender(String gender) {    this.gender = gender;   }     public int getAge() {    return age;   }     public void setAge(int age) {    this.age = age;   }     public double getWeight() {    return weight;   }     public void setWeight(double weight) {    this.weight = weight;   }  }

Example

package com.mytest;    import java.util.List;  import java.util.Map;  import java.util.Set;    import org.slf4j.Logger;  import org.slf4j.LoggerFactory;    import com.google.common.base.Function;  import com.google.common.collect.Lists;  import com.google.common.collect.Maps;  import com.google.common.collect.Ordering;    public class Example {         public static Logger logger = LoggerFactory.getLogger(Example.class);             public static void main(String[] args) {          List<Person> list = Lists.newArrayList();          list.add(new Person(4L,"jason", "male", 16, 120.50));          list.add(new Person(1L,"tom", "male", 48, 163.50));          list.add(new Person(3L,"john", "male", 33, 105));          list.add(new Person(2L,"rose", "female", 26, 90));                              logger.debug(list.toString());          //获取ids          List<Long> ids  = entityIds(list);  //entityIds方法          logger.debug("---------------ids-------------------");          logger.debug(ids.toString());                    logger.debug("---------------maps-------------------");          //获取map          Map<Long, Person> maps = entityMaps(list); //entityMaps方法          Set<Long> keys = maps.keySet();          for (Long id : keys) {     logger.debug("key: " + id + " value: " + maps.get(id));    }   }      /**    * 获取表记录集合的Id集合    * @param list    * @return    */   public static<T extends BaseEntity> List<Long> entityIds(List<T> list){    List<Long> ids = Lists.transform(list, new Function<T, Long>(){               public Long apply(T entity){            return entity.getId();               }                  });     return ids;   }      /**    * 根据实体记录，输出Map<Long id,K extend BaseEntity>集合    * @param list    * @return    */   public static<V extends BaseEntity> Map<Long,V> entityMaps(List<V> list){           Map<Long,V> maps = Maps.uniqueIndex(list.iterator(),  new Function<V, Long>() {        @Override        public Long apply(V entity) {            return entity.getId();        }    });    return maps;   }     }

entityIds方法

        /**    * 获取表记录集合的Id集合    * @param list    * @return    */   public static<T extends BaseEntity> List<Long> entityIds(List<T> list){    List<Long> ids = Lists.transform(list, new Function<T, Long>(){               public Long apply(T entity){            return entity.getId();               }                  });     return ids;   }

entityMaps方法

        /**    * 根据实体记录，输出Map<Long id,K extend BaseEntity>集合    * @param list    * @return    */   public static<V extends BaseEntity> Map<Long,V> entityMaps(List<V> list){           Map<Long,V> maps = Maps.uniqueIndex(list.iterator(),  new Function<V, Long>() {        @Override        public Long apply(V entity) {            return entity.getId();        }    });    return maps;   }

引入包，可参考pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">   <modelVersion>4.0.0</modelVersion>   <groupId>com.gzdfbz</groupId>   <artifactId>mytest</artifactId>   <version>0.0.1-SNAPSHOT</version>     <dependencies>    <dependency>     <groupId>com.google.guava</groupId>     <artifactId>guava</artifactId>     <version>18.0</version>    </dependency>      <dependency>     <groupId>org.apache.commons</groupId>     <artifactId>commons-lang3</artifactId>     <version>3.3.2</version>    </dependency>      <dependency>     <groupId>org.slf4j</groupId>     <artifactId>slf4j-api</artifactId>     <version>1.7.7</version>    </dependency>      <dependency>     <groupId>org.slf4j</groupId>     <artifactId>slf4j-log4j12</artifactId>     <version>1.7.7</version>    </dependency>      <dependency>     <groupId>joda-time</groupId>     <artifactId>joda-time</artifactId>     <version>2.3</version>    </dependency>         </dependencies>  </project>

log4j参考：

#  log4j.rootLogger=DEBUG,console  log4j.additivity.org.apache=true    #  log4j.appender.console=org.apache.log4j.ConsoleAppender  log4j.appender.console.Threshold=DEBUG  log4j.appender.console.ImmediateFlush=true  log4j.appender.console.Target=System.err  log4j.appender.console.layout=org.apache.log4j.PatternLayout  #log4j.appender.console.layout.ConversionPattern=[%-5p] %d(%r) --> [%t] %l: %m %x %n  log4j.appender.console.layout.ConversionPattern=%l: %m %x %n      log4j.appender.com.mytest =  debug

 来自：http://my.oschina.net/u/221951/blog/333286