Java中Inputstream与Reader的区别

Reader支持``16``位的Unicode字符输出，InputStream支持``8``位的字符输出。

Reader和InputStream分别是I/O库提供的两套平行独立的等级机构，

InputStream、OutputStream是用来处理``8``位元的流，

Reader、Writer是用来处理``16``位元的流。

而在[JAVA语言]中，``byte``类型是``8``位的，``char``类型是``16``位的，所以在处理中文的时候需要用Reader和Writer。

值得说明的是，在这两种等级机构下，还有一道桥梁InputStreamReader、OutputStreamWriter负责进行InputStream到Reader的适配和由OutputStream到Writer的适配。

package org.apache.ibatis.session;

import org.apache.ibatis.builder.xml.XMLConfigBuilder;
import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.defaults.DefaultSqlSessionFactory;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;

/**
 * Builds {@link SqlSession} instances.
 * 创建一个DefaultSqlSessionFactory实例
 * @author Clinton Begin
 */
public class SqlSessionFactoryBuilder {

    /*reader方式构造器*/
    public SqlSessionFactory build(Reader reader) {
        return build(reader, null, null);
    }

    public SqlSessionFactory build(Reader reader, String environment) {
        return build(reader, environment, null);
    }

    public SqlSessionFactory build(Reader reader, Properties properties) {
        return build(reader, null, properties);
    }

    public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
        try {
            XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
//从这里可以看出XMLConfigBuilder.parse()返回了一个Configuration对象
            return build(parser.parse());
        } catch (Exception e) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", e);
        } finally {
            ErrorContext.instance().reset();
            try {
                reader.close();
            } catch (IOException e) {
                // Intentionally ignore. Prefer previous error.
            }
        }
    }

    /*InputStream构造器*/
    public SqlSessionFactory build(InputStream inputStream) {
        return build(inputStream, null, null);
    }

    public SqlSessionFactory build(InputStream inputStream, String environment) {
        return build(inputStream, environment, null);
    }

    public SqlSessionFactory build(InputStream inputStream, Properties properties) {
        return build(inputStream, null, properties);
    }

    public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        try {
            XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
            return build(parser.parse());
        } catch (Exception e) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", e);
        } finally {
            ErrorContext.instance().reset();
            try {
                inputStream.close();
            } catch (IOException e) {
                // Intentionally ignore. Prefer previous error.
            }
        }
    }

    /*最终实现*/
    public SqlSessionFactory build(Configuration config) {
        return new DefaultSqlSessionFactory(config);
    }
}