Java

package builder;

public class DbPool {
    private String name;
    private String host;
    private Integer port;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getHost() {
        return host;
    }

    public void setHost(String host) {
        this.host = host;
    }

    public Integer getPort() {
        return port;
    }

    public void setPort(Integer port) {
        this.port = port;
    }

    @Override
    public String toString() {
        return "DbPool{" +
                "name='" + name + '\'' +
                ", host='" + host + '\'' +
                ", port=" + port +
                '}';
    }

    public static Builder builder() {
        return new Builder();
    }

    public static class Builder {
        private String name;
        private String host;
        private Integer port;

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

        public Builder host(String host) {
            this.host = host;
            return this;
        }


        public Builder port(Integer port) {
            this.port = port;
            return this;
        }

        public DbPool build() {
            // 增加字段校验
            if (this.name == null || this.name.isEmpty()) {
                throw new RuntimeException("name不能为空");
            }

            final DbPool dbPool = new DbPool();
            dbPool.setName(this.name);
            dbPool.setHost(this.host == null || this.host.isEmpty() ? "127.0.0.1" : this.host);
            dbPool.setPort(this.port == null || this.port == 0 ? 8080 : this.port);
            return dbPool;
        }
    }
}

Go

package builder

import "errors"

type DbPool struct {
    Name string
    Host string
    Port int
}

type DbPoolBuilder struct {
    name string
    host string
    port int
}

func (d *DbPoolBuilder) SetName(name string) *DbPoolBuilder {
    d.name = name
    return d
}

func (d *DbPoolBuilder) SetHost(host string) *DbPoolBuilder {
    d.host = host
    return d
}

func (d *DbPoolBuilder) SetPort(port int) *DbPoolBuilder {
    d.port = port
    return d
}

func (d *DbPoolBuilder) Build() (*DbPool, error) {
    if d.name == "" {
        return nil, errors.New("name不能为空")
    }

    var dp = DbPool{Name: d.name}

    if d.host == "" {
        dp.Host = "127.0.0.1"
    } else {
        dp.Host = d.host
    }

    if d.port == 0 {
        dp.Port = 8080
    } else {
        dp.Port = d.port
    }
    return &dp, nil
}

为什么需要 Builder 模式？

使用构造器，参数太多的情况下，会导致代码的可读性和易用性降低。（构造器参数存在顺序，顺序出错传参就出错了。）

Java 常见使用建造者模式的方式

工作中一般直接使用 lombok 的 @Builder 注解直接生成 Builder 代码，无需写如此多的模板代码。

Go 中最常见的传参方式

package builder

import "errors"

type Option struct {
    Host string
    Port int
}

type OptionFunc func(option *Option)

// NewDbPool 新建DbPool
// name 必填项
// options 选填项
func NewDbPool(name string, options ...OptionFunc) (*DbPool, error) {
    if name == "" {
        return nil, errors.New("name不能为空")
    }

    defaultOption := Option{
        Host: "127.0.0.1",
        Port: 8080,
    }

    for _, optionFunc := range options {
        optionFunc(&defaultOption)
    }

    return &DbPool{
        Name: name,
        Host: defaultOption.Host,
        Port: defaultOption.Port,
    }, nil
}

// 测试
func TestOption(t *testing.T) {
    pool, err := builder.NewDbPool("option_db_pool", func(option *builder.Option) {
        option.Host = "localhost"
        option.Port = 1234
    })
    if err != nil {
        t.Error(err)
    }

    fmt.Println(pool)

    assert.Equal(t, pool.Host, "localhost")
}

源码

java版本
go版本