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Java toString方法重寫工具之ToStringBuilder案例詳解

更新時(shí)間：2021年08月26日 10:24:33 作者：vince_zw

這篇文章主要介紹了Java toString方法重寫工具之ToStringBuilder案例詳解,本篇文章通過簡要的案例,講解了該項(xiàng)技術(shù)的了解與使用,以下就是詳細(xì)內(nèi)容,需要的朋友可以參考下

apache的commons-lang3的工具包里有一個(gè)ToStringBuilder類，這樣在打日志的時(shí)候可以方便的打印出類實(shí)例中的各屬性的值。

具體用法如下：

import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
 
public class Message {
 
	private String from;
 
	private String to;
 
	private String body;
 
	public String getFrom() {
		return from;
	}
 
	public void setFrom(String from) {
		this.from = from;
	}
 
	public String getTo() {
		return to;
	}
 
	public void setTo(String to) {
		this.to = to;
	}
 
	public String getBody() {
		return body;
	}
 
	public void setBody(String body) {
		this.body = body;
	}
 
	@Override
	public String toString() {
		return ToStringBuilder.reflectionToString(this, ToStringStyle.MULTI_LINE_STYLE);
	}
	
	public static void main(String[] args) {
		Message msg = new Message();
		msg.setFrom("vince");
		msg.setTo("mike");
		msg.setBody("hello");
		System.out.println(msg.toString());
	}
}

而且支持多種打印格式

多行輸出的：

com.vince.im.dto.Message@af72d8[
from=vince
to=mike
body=hello
]

默認(rèn)一行的：

com.vince.im.dto.Message@af72d8[from=vince,to=mike,body=hello]

NO_FIELD_NAMES_STYLE：

com.vince.im.dto.Message@af72d8[vince,mike,hello]

SHORT_PREFIX_STYLE：

Message[from=vince,to=mike,body=hello]

SIMPLE_STYLE：

vince,mike,hello

原理其實(shí)就是通過JAVA的reflect（反射）獲取值，然后組成一個(gè)Buffer。

里面部分源碼：

    /**
     * <p>Append to the <code>toString</code> the start of data indicator.</p>
     * 拼裝結(jié)果的
     * @param buffer  the <code>StringBuffer</code> to populate
     * @param object  the <code>Object</code> to build a <code>toString</code> for
     */
    public void appendStart(final StringBuffer buffer, final Object object) {
        if (object != null) {
            appendClassName(buffer, object);
            appendIdentityHashCode(buffer, object);
            appendContentStart(buffer);
            if (fieldSeparatorAtStart) {
                appendFieldSeparator(buffer);
            }
        }
    }
 
    /**
     * <p>Append the {@link System#identityHashCode(java.lang.Object)}.</p>
     * 拼裝對(duì)象hashcode
     * @param buffer  the <code>StringBuffer</code> to populate
     * @param object  the <code>Object</code> whose id to output
     */
    protected void appendIdentityHashCode(final StringBuffer buffer, final Object object) {
        if (this.isUseIdentityHashCode() && object!=null) {
            register(object);
            buffer.append('@');
            buffer.append(Integer.toHexString(System.identityHashCode(object)));
        }
    }

需要注意的是：

Builds a toString value using the default ToStringStyle through reflection.

It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly.

Transient members will be not be included, as they are likely derived. Static fields will not be included. Superclass fields will be appended.

也就是說transient和static修飾的屬性不能打印出來，但是父類的是可以打印出來的，使用的時(shí)候一定要注意了。

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