建造者模式
一般在什么场景下使用建造者模式？
①需要的这个对象非常复杂，即它包含非常多的属性
②对象构建出来就保持不变或很少改变
符合此类要求的我能想到的就是一些配置类或者其他一些工具库。如Spring-Data-Redis中JedisClientConfiguration或者Picasso中的Picasso中就使用了建造者模式，可以通过以下代码感受一些使用建造者模式创建对象的方式：
//获取JedisClientConfiguration的方式
public JedisClientConfiguration jedisClientConfiguration() {
JedisClientConfiguration.JedisPoolingClientConfigurationBuilder configurationBuilder = (
JedisClientConfiguration.JedisPoolingClientConfigurationBuilder) JedisClientConfiguration.builder();
GenericObjectPoolConfig GenericObjectPoolConfig = new GenericObjectPoolConfig();
GenericObjectPoolConfig.setMaxIdle(1000);
GenericObjectPoolConfig.setMaxTotal(100);
GenericObjectPoolConfig.setMinIdle(100);
return configurationBuilder
.poolConfig(GenericObjectPoolConfig)
.and()
.usePooling()//显式指明使用pool
.build();
}
//Picasso的使用方式
Picasso.get().load("http://i.imgur.com/DvpvklR.png").into(imageView);使用建造者模式的一般步骤或思想
①最终对象一般都比较复杂，构建过程中可能需要其他对象；
②一般将必要参数设置在构建builder的方法中，再由build为最终对象设置非必须参数
③最后由build()方法返回最终对象
实例1
public class User {
private final String firstName; // 必传参数
private final String lastName; // 必传参数
private final int age; // 可选参数
private final String phone; // 可选参数
private final String address; // 可选参数
private User(UserBuilder builder) {
this.firstName = builder.firstName;
this.lastName = builder.lastName;
this.age = builder.age;
this.phone = builder.phone;
this.address = builder.address;
}
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public int getAge() {
return age;
}
public String getPhone() {
return phone;
}
public String getAddress() {
return address;
}
public static class UserBuilder {
private final String firstName;
private final String lastName;
private int age;
private String phone;
private String address;
public UserBuilder(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
public UserBuilder age(int age) {
this.age = age;
return this;
}
public UserBuilder phone(String phone) {
this.phone = phone;
return this;
}
public UserBuilder address(String address) {
this.address = address;
return this;
}
public User build() {
return new User(this);
}
}
}使用方式：
User user = new User.UserBuilder("王", "小二")
.age(20)
.phone("123456789")
.address("亚特兰蒂斯大陆")
.build();实例2
public interface JedisClientConfiguration {
boolean isUseSsl();
Optional<SSLSocketFactory> getSslSocketFactory();
Optional<SSLParameters> getSslParameters();
Optional<HostnameVerifier> getHostnameVerifier();
boolean isUsePooling();
Optional<GenericObjectPoolConfig> getPoolConfig();
Optional<String> getClientName();
Duration getConnectTimeout();
Duration getReadTimeout();
static JedisClientConfigurationBuilder builder() {
return new DefaultJedisClientConfigurationBuilder();
}
/**
* Creates a default {@link JedisClientConfiguration}.
* <dl>
* <dt>SSL enabled</dt>
* <dd>no</dd>
* <dt>Pooling enabled</dt>
* <dd>no</dd>
* <dt>Client Name</dt>
* <dd>[not set]</dd>
* <dt>Read Timeout</dt>
* <dd>2000 msec</dd>
* <dt>Connect Timeout</dt>
* <dd>2000 msec</dd>
* </dl>
*
* @return a {@link JedisClientConfiguration} with defaults.
*/
static JedisClientConfiguration defaultConfiguration() {
return builder().build();
}
/**
* Builder for {@link JedisClientConfiguration}.
*/
interface JedisClientConfigurationBuilder {
JedisSslClientConfigurationBuilder useSsl();
JedisPoolingClientConfigurationBuilder usePooling();
JedisClientConfigurationBuilder clientName(String clientName);
JedisClientConfigurationBuilder readTimeout(Duration readTimeout);
JedisClientConfigurationBuilder connectTimeout(Duration connectTimeout);
JedisClientConfiguration build();
}
/**
* Builder for Pooling-related {@link JedisClientConfiguration}.
*/
interface JedisPoolingClientConfigurationBuilder {
JedisPoolingClientConfigurationBuilder poolConfig(GenericObjectPoolConfig poolConfig);
JedisClientConfigurationBuilder and();
JedisClientConfiguration build();
}
/**
* Builder for SSL-related {@link JedisClientConfiguration}.
*/
interface JedisSslClientConfigurationBuilder {
JedisSslClientConfigurationBuilder sslSocketFactory(SSLSocketFactory sslSocketFactory);
JedisSslClientConfigurationBuilder sslParameters(SSLParameters sslParameters);
JedisSslClientConfigurationBuilder hostnameVerifier(HostnameVerifier hostnameVerifier);
JedisClientConfigurationBuilder and();
JedisClientConfiguration build();
}
class DefaultJedisClientConfigurationBuilder implements JedisClientConfigurationBuilder,
JedisPoolingClientConfigurationBuilder, JedisSslClientConfigurationBuilder {
private boolean useSsl;
private @Nullable SSLSocketFactory sslSocketFactory;
private @Nullable SSLParameters sslParameters;
private @Nullable HostnameVerifier hostnameVerifier;
private boolean usePooling;
private GenericObjectPoolConfig poolConfig = new JedisPoolConfig();
private @Nullable String clientName;
private Duration readTimeout = Duration.ofMillis(Protocol.DEFAULT_TIMEOUT);
private Duration connectTimeout = Duration.ofMillis(Protocol.DEFAULT_TIMEOUT);
private DefaultJedisClientConfigurationBuilder() {}
@Override
public JedisSslClientConfigurationBuilder useSsl() {
this.useSsl = true;
return this;
}
@Override
public JedisSslClientConfigurationBuilder sslSocketFactory(SSLSocketFactory sslSocketFactory) {
this.sslSocketFactory = sslSocketFactory;
return this;
}
@Override
public JedisSslClientConfigurationBuilder sslParameters(SSLParameters sslParameters) {
this.sslParameters = sslParameters;
return this;
}
@Override
public JedisSslClientConfigurationBuilder hostnameVerifier(HostnameVerifier hostnameVerifier) {
this.hostnameVerifier = hostnameVerifier;
return this;
}
@Override
public JedisPoolingClientConfigurationBuilder usePooling() {
this.usePooling = true;
return this;
}
@Override
public JedisPoolingClientConfigurationBuilder poolConfig(GenericObjectPoolConfig poolConfig) {
this.poolConfig = poolConfig;
return this;
}
@Override
public JedisClientConfigurationBuilder and() {
return this;
}
@Override
public JedisClientConfigurationBuilder clientName(String clientName) {
this.clientName = clientName;
return this;
}
@Override
public JedisClientConfigurationBuilder readTimeout(Duration readTimeout) {
this.readTimeout = readTimeout;
return this;
}
@Override
public JedisClientConfigurationBuilder connectTimeout(Duration connectTimeout) {
this.connectTimeout = connectTimeout;
return this;
}
@Override
public JedisClientConfiguration build() {
return new DefaultJedisClientConfiguration(useSsl, sslSocketFactory, sslParameters, hostnameVerifier, usePooling,
poolConfig, clientName, readTimeout, connectTimeout);
}
}
}参考
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