Java 设计模式-建造者模式（Builder）

    建造者模式（Builder Pattern）是属于创建型模式，它的意图是：将一个复杂的对象的创建和表示分离，是的同样的构建过程可以创建不同的表示。

   如果有一个类Test有1个属性 name,不管我们如何穿件这个对象的实例都不会很麻烦。

public class Test {

    private String name;

    public Test(String name) {
        super();
        this.name = name;
    }

    public Test() {
        super();
    }

    /**
     * Getter method for property <tt>name</tt>.
     *
     * @return property value of name
     */
    public String getName() {
        return name;
    }

    /**
     * Setter method for property <tt>name</tt>.
     *
     * @param name value to be assigned to property name
     */
    public void setName(String name) {
        this.name = name;
    }

}

public class TestClient {

    /**
     * 
     * @param args
     */
    public static void main(String[] args) {
        Test test=new Test();
        test.setName("MyTest");
        
        Test test2=new Test("MyTest2");
    }

}

 那么，如果一个类的属性有很多，甚至是数十个的时候构建一个对象将是一件很痛苦的过程，如下就是在项目中遇到的一个构建一个对象。

   TaxBillModel taxBillModel = new TaxBillModel();

        taxBillModel.setApplyBillDate(new Date());
        taxBillModel.setBillBatchNo(billBatchNo);
        taxBillModel.setBillDate(new Date());
        taxBillModel.setChargeOffDate(new Date());
        taxBillModel.setCheckDate(new Date());
        taxBillModel.setExchangeDate(new Date());
        taxBillModel.setExchangeRate(Double.parseDouble(exchangeRate));
        taxBillModel.setExpiryDate(new Date());
        taxBillModel.setFailureAmount(new Money(Double.parseDouble(failureAmount)));
        taxBillModel.setFailureCount(Long.parseLong(failureCount));
        taxBillModel.setGmtCreate(new Date());
        taxBillModel.setGmtModified(new Date());
        taxBillModel.setOriginalAmount(new Money(Double.parseDouble(originalAmount)));
        taxBillModel.setPartnerName(partnerName);
        taxBillModel.setRealCurrency(realCurrency);
        taxBillModel.setRealAmount(new Money(Long.parseLong(realAmount)));
        taxBillModel.setPartnerId(parnterId);
        taxBillModel.setRemitNo(remitNo);
        taxBillModel.setSuccessCount(Long.parseLong(successCount));
        taxBillModel.setCurrency(currency);
        taxBillModel.setStatus("RA");

 在这样的一个情况下我们应该使用Builder Pattern 去解决问题。

public class MyModel {

    private int        id;
    /**名称**/
    private String     name;

    /**币种**/
    private String     currency;

    /**金额**/
    private BigDecimal amount;

    /**
     * Getter method for property <tt>id</tt>.
     *
     * @return property value of id
     */
    public int getId() {
        return id;
    }

    /**
     * Setter method for property <tt>id</tt>.
     *
     * @param id value to be assigned to property id
     */
    public void setId(int id) {
        this.id = id;
    }

    /**
     * Getter method for property <tt>name</tt>.
     *
     * @return property value of name
     */
    public String getName() {
        return name;
    }

    /**
     * Setter method for property <tt>name</tt>.
     *
     * @param name value to be assigned to property name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * Getter method for property <tt>currency</tt>.
     *
     * @return property value of currency
     */
    public String getCurrency() {
        return currency;
    }

    /**
     * Setter method for property <tt>currency</tt>.
     *
     * @param currency value to be assigned to property currency
     */
    public void setCurrency(String currency) {
        this.currency = currency;
    }

    /**
     * Getter method for property <tt>amount</tt>.
     *
     * @return property value of amount
     */
    public BigDecimal getAmount() {
        return amount;
    }

    /**
     * Setter method for property <tt>amount</tt>.
     *
     * @param amount value to be assigned to property amount
     */
    public void setAmount(BigDecimal amount) {
        this.amount = amount;
    }

}

public class MyModelBuilder {

    private int        id;

    private String     name;

    private String     currency;

    private BigDecimal amount;

    public MyModelBuilder addId(int id) {
        this.id = id;
        return this;
    }

    public MyModelBuilder addName(String name) {
        this.name = name;
        return this;
    }

    public MyModelBuilder addMoney(String currency, BigDecimal amount) {
        this.currency = currency;
        this.amount = amount;
        return this;
    }

    public MyModel toMyModel() {
        MyModel myModel = new MyModel();
        myModel.setAmount(amount);
        myModel.setCurrency(currency);
        myModel.setId(id);
        myModel.setName(name);
        return myModel;
    }
}
public class Client {

    /**
     *
     * @param args
     */
    public static void main(String[] args) {
        MyModelBuilder builder = new MyModelBuilder();
        builder.addMoney("USD", BigDecimal.valueOf(100));
        builder.addId(0);
        builder.addName("Test");
        MyModel myModel = builder.toMyModel();
        System.out.println(myModel);
    }

}