Google Guava集合在實體類中的應用示例

將實體list，轉換成map，拿到所有id的集合方法。減少訪問數據庫。

實體基類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;
    }
    /**
     * 覆蓋toString方法，目的顯示所有JavaBean的屬性值，省略寫很多的getXxx的方法
     */
    public String toString() {
        return ToStringBuilder.reflectionToString(this,
                ToStringStyle.MULTI_LINE_STYLE);
    }
}

實體類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());
        //獲取ids
        List<Long> ids  = entityIds(list);  //entityIds方法
        logger.debug("---------------ids-------------------");
        logger.debug(ids.toString());
        
        logger.debug("---------------maps-------------------");
        //獲取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));
        }
    }

    /**
     * 獲取表記錄集合的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;
    }

    /**
     * 根據實體記錄，輸出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

        /**
     * 獲取表記錄集合的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

        /**
     * 根據實體記錄，輸出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，可參考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參考：

#
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

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